Square [brackets] are used to enclose explanations of what is going on at certain points. Curly {brackets} enclose material that is to be read as though it were part of the original text. Each {bracketed} bit helps to express the author's line of thought; it is something he would have been willing to write; but the {brackets} are an admission that he did not in fact write it.

Everyone will freely admit that the perceptions of the mind when a man feels the pain of excessive heat or the pleasure of moderate warmth are considerably unlike what he feels when he later remembers this sensation or earlier looks forward to it in his imagination. Memory and imagination may mimic or copy the perceptions of the senses, but they cannot create a perception that has as much force and vivacity as the one they are copying. Even when they operate with greatest vigor, the most we will say is that they represent their object so vividly that we could almost say we feel or see it. Except when the mind is out of order because of disease or madness, memory and imagination can never be so lively as to create perceptions that are indistinguishable from the ones we have in seeing or feeling. The most lively thought is still dimmer than the dullest sensation.

A similar distinction runs through all the other perceptions of the mind. A real fit of anger is very different merely thinking of that emotion. If you tell me that someone is in love, I understand your meaning and form a correct conception of the state he is in; but I would never mistake that conception for the turmoil of actually being in love! When we think back on our past sensations and feelings, our thought is a faithful mirror which copies its objects truly; but it does so in colors that are fainter and more washed-out than those in which our original perceptions were clothed. To tell one from the other you do not need careful thought or philosophical ability.

So we can divide the mind's perceptions into two classes, on the basis of their different degrees of force and vivacity. The less forcible and lively are commonly called "thoughts" or "ideas". The others have no name in our language or in most others, presumably because we do not need a general label for them except when we are doing philosophy. Let us, then, take the liberty of calling them "impressions", using that word in a slightly unusual sense. By the term "impression", then, I mean all our more lively perceptions when we hear or see or feel or love or hate or desire or will. These are to be distinguished from ideas, which are the fainter perceptions of which we are conscious when we reflect on our impressions.

It may seem at first sight that human thought is utterly unbounded: it not only escapes all human power and authority {as when a poor man thinks of becoming wealthy overnight, or when an ordinary citizen thinks of being a king}, but is not even confined within the limits of nature and reality. It is as easy for the imagination to form monsters and to join incongruous shapes and appearances as it is to conceive the most natural and familiar objects. And while the body must creep laboriously over the surface of one planet, thought can instantly transport us to the most distant regions of the universe - and even further. What never was seen or heard of may still be conceived; nothing is beyond the power of thought except what implies an absolute contradiction.

But although our thought seems to be so free, when we look more carefully we shall find that it is really confined within very narrow limits, and that all this creative power of the mind amounts to merely the ability to combine, transpose, augment, or diminish the materials that the senses and experience provide us with. When we think of a golden mountain, we only join two consistent ideas - gold and mountain - with which we were already familiar. We can conceive a virtuous horse because our own feelings enable us to conceive virtue, and we can join this with the shape of a horse, which is an animal we know. In short, all the materials of thinking are derived either from our outward senses or from our inward feelings: all that the mind and will do is to mix and combine these materials. Put in philosophical terminology: all our ideas or more feeble perceptions are copies of our impressions or more lively ones.

Here are two arguments which I hope will suffice to prove this. (1) When we analyse our thoughts or ideas - however complex or elevated they are - we always find them to be made up of simple ideas that were copied from earlier feelings or sensations. Even ideas which at first glance seem to be the furthest removed from that origin are found upon closer examination to be derived from it. The idea of God - meaning an infinitely intelligent, wise, and good Being - comes from extending beyond all limits the qualities of goodness and wisdom that we find in our own minds. However far we push this enquiry, we shall find that every idea that we examine is copied from a similar impression. Those who maintain that this is not universally true and that there are exceptions to it have only one way of refuting it - but it should be easy for them, if they are right. They need merely to produce an idea which they think is not derived from this source. It will then be up to me, if I am to maintain my doctrine, to point to the impression or lively perception which corresponds to the idea they have produced.

(2) If man cannot have some kind of sensation because there is something wrong with his eyes, ears etc., he will never be found to have corresponding ideas. A blind man cannot form a notion of colors, or a deaf man a notion of sounds. If either is cured of his deafness or blindness, so that the sensations can get through to him, the ideas can then get through as well; and then he will find it easy to conceive these objects. The same is true if one has never experienced an object that will give a certain kind of sensation: a Laplander or Negro has no notion of the taste of wine. Similarly with inward feelings. It seldom if ever happens that a person has never felt or is wholly incapable of some human feeling or emotion, but the phenomenon I am describing does occur with feelings as well, though in lesser degree. A gentle person cannot form any idea of determined revenge or cruelty; nor can a selfish one easily conceive the heights of friendship and generosity. Everyone agrees that non-human beings may have many senses of which we can have no conception, because the ideas of them have never been introduced to us in the only way in which an idea can get into the mind, namely through actual feeling and sensation.

(There is, however, one counter-example which may prove that it is not absolutely impossible for an idea to occur without a corresponding impression. I think it will be granted that the various distinct ideas of colour which enter the mind through the eye (or those of sound, which come in through the ear) really are different from each other, though they resemble one another in certain respects. If that holds for different colours, it must hold equally for the different shades of a single colour; so each shade produces a distinct idea, independent of the rest. (We can create a continuous gradation of shades, running from red at one end to green at the other, with each member of the series shading imperceptibly into its neighbour. If the immediate neighbours in the sequence are not distinct, then red is not distinct from green, which is absurd.) Now, suppose that a sighted person has become perfectly familiar with colours of all kinds, except for one particular shade of blue (for instance), which he happens never to have met with. Let all the other shades of blue be placed before him, descending gradually from the deepest to the lightest: it is obvious that he will notice a blank in the place where the missing shade should go. That is, he will be aware that there is a greater quality-distance between that pair of neighbouring shades than between any other pair in the series. Can he fill the blank from his own imagination, calling up in his mind the idea of that particular shade, even though it has never been conveyed to him by his senses? Most people, I think, will agree that he can. This seems to show that simple ideas are not always, in every instance, derived from corresponding impressions. Still, the example is so singular that it is hardly worth noticing, and on its own it is not a good enough reason for us to alter our general maxim.)

So here is a proposition which not only seems to be simple and intelligible in itself, but could if properly used make every dispute equally intelligible by banishing all that nonsensical jargon which has so long dominated metaphysical reasonings. {Those reasonings are beset by three troubles.} (i) All ideas, especially abstract ones, are naturally faint and obscure, so that the mind has only a weak hold on them. (ii) Ideas are apt to be mixed up with other ideas that resemble them. (iii) We tend to assume that a given word is associated with a determinate idea just because we have used it so often, even if in using it we have not had any distinct meaning for it. In contrast with this, (i) all our impressions - that is, all our outward or inward sensations - are strong and vivid. (ii) The boundaries between them are more exactly placed, and (iii) it is harder to make mistakes about them. So when we come to suspect that a philosophical term is being used without any meaning or idea (as happens all too often), we need only to ask: From what impression is that supposed idea derived? If none can be pointed out, that will confirm our suspicion {that the term in meaningless, that is, has no associated idea}. By bringing ideas into this clear light we may reasonably hope to settle any disputes that arise about whether they exist and what they are like.

The fact that different ideas are connected is too obvious to be overlooked; yet I have not found any philosopher trying to list or classify all the principles of association. This seems to be worth doing. To me there appear to be only three principles of connexion among ideas, namely, Resemblance, Contiguity [= nextness] in time or place, and Cause or Effect.

I don't think there will be much doubt that our ideas are connected by these principles. A picture naturally leads our thoughts to the thing that is depicted in it; the mention of one room naturally introduces remarks or questions about other rooms in the same building; and if we think of a wound, we can hardly help thinking about the pain that follows it. But it will be hard to prove to anyone's satisfaction - the reader's or my own - that this these three are the only principles of association among our ideas. All we can do is to consider a large number of instances where ideas are connected, find in each case what connects them, and eventually develop a really general account of this phenomenon. The more cases we look at, and the more care we employ on them, the more assured we can be that our final list of principles of association is complete.

All the objects of human reason or enquiry fall naturally into two kinds, namely Relations of Ideas and Matters of Fact. The first kind include Geometry, Algebra, and Arithmetic, and indeed every statement which is either intuitively or demonstratively certain. That the square of the hypotenuse is equal to the squares of the two sides expresses a relation between those figures. That three times five equals half of thirty expresses a relation between those numbers. Propositions of this kind can be discovered purely by thinking, with no need to attend to anything that actually exists anywhere in the universe. The truths that Euclid demonstrated would still be certain and self-evident even if there never were a circle or triangle in nature.

Matters of fact, which are the second objects of human reason, are not established in the same way; and we cannot have such strong grounds for thinking them true. The contrary of every matter of fact is still possible, because it does not imply a contradiction and is conceived by the mind as easily and clearly as if it conformed perfectly to reality. That the sun will not rise to-morrow is just as intelligible as - and no more contradictory than - the proposition that the sun will rise tomorrow. It would therefore be a waste of time to try to demonstrate [= prove purely by logic] its falsehood. If it were demonstratively false, it would imply a contradiction and so could never be clearly conceived by the mind.

So it may be worth our time and trouble to try to answer this: What sorts of grounds do we have for being sure of matters of fact - propositions about what exists and what is the case - that are not attested by our present senses or the records of our memory? It is a notable fact that neither ancient philosophers nor modern ones have attended much to this important question; so in investigating it I shall be marching through difficult terrain with no guides or signposts; and that may help to excuse any errors I commit or doubts that I raise. Those errors and doubts may even be useful: they may make people curious and eager to learn, and may destroy that ungrounded and unexamined confidence {that people have in their opinions - a confidence} which is the curse of all reasoning and free enquiry. If we find things wrong with commonly accepted philosophical views, that need not be a discouragement, but rather can spur us on to try for something more full and satisfactory than has yet been published.

All reasonings about matters of fact seem to be based on the relation of Cause and Effect, which is the only relation that can take us beyond the evidence of our memory and senses. If you ask someone why he believes some matter of fact which is not now present to him - for instance that his friend is now in France - he will give you a reason; and this reason will be some other fact, such as that he has received a letter from his friend or that his friend had planned to go to France. Someone who finds a watch or other machine on a desert island will conclude that there have been men on that island. All our reasonings concerning fact are like this. When we reason in this way, we suppose that the present fact is connected with the one that we infer from it. If there were nothing to bind the two facts together, the inference of one from the other would be utterly shaky. Hearing the sounds of someone talking rationally in the dark assures us of the presence of some person. Why? Because such sounds are the effects of the human constitution, and are closely connected with it. All our other reasonings of this sort, when examined in detail, turn out to be based on the relation of cause and effect. The causal chain from evidence to the "matter of fact" conclusion may be short or long. And it may be that the causal connection between them is not direct but collateral - as when one sees light and infers heat, not because either causes the other but because the two are collateral effects of a single cause, namely fire. So if we want to understand the basis of our confidence about matters of fact, we must find out how we come to know about cause and effect.

I venture to assert, as true without exception, that knowledge about causes is never acquired through a priori reasoning, and always comes from our experience of finding that particular objects are constantly associated with one other. [When Hume is discussing cause and effect, his word "object" often covers events as well as things.] Present an object to a man whose skill and intelligence are as great as you like; if the object is of a kind that is entirely new to him, no amount of studying of its perceptible qualities will enable him to discover any of its causes or effects. Adam, even if his reasoning abilities were perfect from the start, could not have inferred from the fluidity and transparency of water that it could drown him, or from the light and warmth of fire that it could burn him. The qualities of an object which appear to the senses never reveal the causes which produced the object or the effects which it will have; nor can our reason, unaided by experience, ever draw any conclusion about real existence and matters of fact.

The proposition that causes and effects are discoverable not by reason but by experience will be freely granted (i) with regard to objects which we remember having once been altogether unknown to us; for in those cases we remember the time when we were quite unable to tell what would arise from those objects. Present two smooth pieces of marble to a man who has no knowledge of physics - he will not be able to work out that they will stick together in such a way that it takes great force to separate them by pulling them directly away from one another, while it will be easy to slide them apart. (ii) Events that are not much like the common course of nature are also readily agreed to be known only by experience; and nobody thinks that the explosion of gunpowder, or the attraction of a magnet, could ever be discovered by arguments a priori {- that is, by simply thinking about the matter, without bringing in anything known from experience}. (iii) Similarly, when an effect is thought to depend upon an intricate machinery or secret structure of parts we do not hesitate to attribute all our knowledge of it to experience. No-one would assert that he can give the ultimate reason why milk or bread is nourishing for a man but not for a lion or a tiger.

But this same proposition {- that causes and effects cannot be discovered by reason -} may seem less obvious when it is applied to events of kinds (i) that we have been familiar with all our lives, (ii) that are very like the whole course of nature, and (iii) that are supposed to depend on the simple {perceptible} qualities of objects and not on any secret structure of parts. We are apt to imagine that we could discover these effects purely through reason, without experience. We fancy that if we had been suddenly brought into this world, we could have known straight off that when one billiard ball strikes another it will make it move - knowing this for certain, without having to try it out on billiard balls. Custom has such a great influence! At its strongest it not only hides our natural ignorance but even conceals itself: just because custom is so strongly at work, we are not aware of its being at work at all.

If you are not yet convinced that absolutely all the laws of nature and operations of bodies can be known only by experience, consider the following. If we are asked to say what the effects will be of some object, without consulting past experience of it, how can the mind go about doing this? It must invent or imagine some event as being the object's effect; and clearly this invention must be entirely arbitrary. The mind cannot possibly find the effect in the supposed cause, however carefully we examine it, for the effect is totally different from the cause and therefore can never be discovered in it. Motion in the second billiard ball is a distinct event from motion in the first, and nothing in the first ball's motion even hints at motion in the second. A stone raised into the air and left without any support immediately falls; but if we consider this situation a priori we shall find nothing that generates the idea of a downward rather than an upward or some other motion in the stone.

Just as the first imagining or inventing of a particular effect is arbitrary if it is not based on experience, the same holds for the supposed tie or connexion between cause and effect - the tie which binds them together and makes it impossible for that cause to have any effect other than that one. Suppose for example that I see one billiard ball moving in a straight line towards another: even if the contact between them should happen to suggest to me the idea of motion in the second ball, are there not a hundred different events that I can conceive might follow from that cause? May not both balls remain still? May not the first bounce straight back the way it came, or bounce off in some other direction? All these suppositions are consistent and conceivable. Why then should we prefer just one, which is no more consistent or conceivable than the rest? Our a priori reasonings will never reveal any basis for this preference.

In short, every effect is a distinct event from its cause. So it cannot be discovered in the cause, and the first invention or conception of it a priori must be wholly arbitrary. Furthermore, even after it has been suggested, the linking of it with the cause must still appear as arbitrary, because plenty of other possible effects must seem just as consistent and natural from reason's point of view. So there is not the slightest hope of reaching any conclusions about causes and effects without the help of experience.

That is why no reasonable scientist has ever claimed to know the ultimate cause of any natural process, or to show clearly and in detail what goes into the causing of any single effect in the universe. It is agreed that the most human reason can achieve is to make the principles that govern natural phenomena simpler, bringing many particular effects together under a few general causes by reasoning from analogy, experience and observation. But if we try to discover the causes of these general causes, we shall be wasting our labor. These ultimate sources and principles are totally hidden from human enquiry. Probably the deepest causes and principles that we shall ever discover in nature are these four: elasticity, gravity, cohesion of parts {which makes the difference between a pebble and a pile of dust}, and communication of motion by impulse {as when one billiard ball hits another}. We shall be lucky if by careful work we can explain particular phenomena in terms of these four, or something close to them. The perfect philosophy of the natural kind [= the perfect physics] only staves off our ignorance a little longer; just as, perhaps, the most perfect philosophy of the moral or metaphysical kind [= the most perfect philosophy, in the 20th century sense of the word] serves only to show us more of how ignorant we are. So both kinds of philosophy eventually lead us to a view of human blindness and weakness - a view which confronts us at every turn despite our attempts to get away from it.

Although geometry is rightly famous for the accuracy of its reasoning, when it is brought to the aid of physics it cannot lead us to knowledge of ultimate causes, thereby curing the ignorance I have been discussing. Every part of applied mathematics works on the assumption that nature operates according to certain established laws; and abstract reasonings are used either to help experience to discover these laws or to work out how the laws apply in particular cases where exactness of measurement is relevant. Here is an example. It is a law of motion, discovered by experience, that the force of any moving body is proportional to its mass and to its velocity; so we can get a small force to overcome the greatest obstacle if we can devise a machine that will increase the velocity of the force so that it overwhelms its antagonist. Geometry helps us to apply this law by showing us how to work out the sizes and shapes of all the parts of the machine that we make for this purpose; but the law itself is something we know purely from experience, and no amount of abstract reasoning could lead us one step towards the knowledge of it. When we reason a priori, considering some object or cause merely as it appears to the mind and independently of any observation of its behaviour, it could never prompt us to think of any other item, such as its effect. Much less could it show us the unbreakable connexion between them. It would take a very clever person to discover by reasoning that heat makes crystals and cold makes ice without having had experience of the effects of heat and cold!

But we have not yet found an acceptable answer to the question that I initially asked. Each solution raises new questions which are as hard to answer as the first one, and which lead us on to further enquiries. To the question What is the nature of all our reasonings concerning matter of fact? the proper answer seems to be that they are based on the relation of cause and effect. When it is further asked, What is the foundation of all our reasonings about cause and effect? we can answer in one word, Experience. But if we persist with questions, and ask, What are inferences from experience based on? this raises a new question which may be harder still. Philosophers - for all their air of superior wisdom - are given a hard time by people who persist with questions, pushing them from every corner into which they retreat, finally bringing them to some dangerous dilemma [that is, a situation where they have to choose between two alternatives, each of which seems wrong]. The best way for us to avoid such an embarrassment is not to claim too much in the first place, and even to find the difficulty for ourselves before it is brought against us as an objection. In this way we can make a kind of merit even of our ignorance.

In this section I shall settle for something easy, offering only a negative answer to the question I have raised {about what inferences from experience are based upon}. It is this: even after we have experience of the operations of cause and effect, the conclusions we draw from that experience are not based on reasoning or on any process of the understanding. I shall try to explain and defend this answer.

It must be granted that nature has kept us at a distance from all its secrets, and has allowed us to know only a few superficial qualities of objects, concealing from us those powers and principles on which the influence of the objects entirely depends. Our senses tell us about the color, weight and consistency of bread; but neither the senses nor reason can ever tell us about the qualities that enable bread to nourish a human body. Sight or touch gives us an idea of the motion of bodies; but as for the amazing force which keeps a body moving for ever unless it collides with other bodies - we cannot have the remotest conception of that. Despite this ignorance of natural powers and principles, however, we always assume that the same sensible qualities will have the same secret powers, and we expect them to have the same effects that we have found them to have in our past experience. If we are given some stuff with the color and consistency of bread which we have eaten in the past, we do not hesitate to repeat the experiment {of eating it}, confidently expecting it to nourish and support us. {That is what we do every morning at the breakfast table: confidently experiment with bread-like stuff by eating it!} I would like to know what the basis is for this process of thought. Everyone agrees that a thing's sensible qualities are not connected with its secret powers in any way that we know about, so that the mind is not led to a conclusion about their constant and regular conjunction through anything it knows of their nature. All that past experience can tell us, directly and for sure, concerns the behaviour of the particular objects we observed, at the particular time when we observed them. {My experience directly and certainly informs me that that fire consumed coal then; but it is silent about the behaviour of the same fire a few minutes later, and about other fires at any time.} Why should this experience be extended to future times and to other objects, which for all we know may only seem similar? - that is what I want to know. The bread which I formerly ate nourished me; that is, a body with such and such sensible qualities did at that time have such and such secret powers. But does it follow that other bread must also nourish me at other times, and that the same perceptible qualities must always be accompanied by the same secret powers? It does not seem to follow necessarily. Anyway, it must be admitted that in such a case as this the mind draws a conclusion; it takes a certain step, goes through a process of thought or inference, which needs to be explained. These two propositions are far from being the same:

I have found that such and such an object has always had such and such an effect.

I foresee that other objects which appear similar will have similar effects.

{They have not given any account of this, which I take to be evidence that none can be given.} If many penetrating and able philosophers try and fail to discover a connecting proposition or intermediate step through which the understanding can perform this inference from past effects to future ones, my negative line of thought about this will eventually be found entirely convincing. But as the question is still new, the reader may not trust his own abilities enough to conclude that because he cannot find a certain argument it does not exist. In that case I need to tackle a harder task than I have so far undertaken - namely, going through all the branches of human knowledge one by one, trying to show that none can give us such an argument.

All reasonings fall into two kinds: (1) demonstrative reasoning, or that concerning relations of ideas, and (2) factual reasoning, or that concerning matters of fact and existence. That no demonstrative arguments are involved in (2) seems evident; since there is no outright contradiction in supposing that the course of nature will change so that an object which seems like ones we have experienced will have different or contrary effects from theirs. May I not clearly and distinctly conceive that snowy stuff falling from the clouds might taste salty or feel hot? Is there anything unintelligible about supposing that all the trees will flourish in December and lose their leaves in June? Now, if something is intelligible and can be distinctly conceived, it implies no contradiction and can never be proved false by any demonstrative argument or abstract a priori reasoning.

So if there are arguments to justify us in trusting past experience and making it the standard of our future judgment, these arguments must be probable only; that is, they must be of the kind that concern matters of fact and real existence, to put it in terms of the classification I have given. But probable reasoning cannot provide us with the argument we are looking for, if I have described it accurately. According to my account, all arguments about existence are based on the relation of cause and effect; our knowledge of that relation is derived entirely from experience; and in drawing conclusions from experience we assume that the future will be like the past. So if we try to prove this assumption by probable arguments, i.e. arguments regarding existence, we shall obviously be going in a circle, taking for granted the very point that is in question.

In reality, all arguments from experience are based on the similarities that we find among natural objects - which lead us to expect that the effects of the objects will also be similar. Although only a fool or a madman would ever challenge the authority of experience or reject it as a guide to human life, still perhaps a philosopher may be allowed to ask what it is about human nature that gives this mighty authority to experience and leads us to profit from the similarities that nature has established among different objects. Our inferences from experience all boil down to this: From causes which appear similar we expect similar effects. If this were based upon reason, we could draw the conclusion as well after a single instance as after a long course of experience. But that is not in fact how things stand. Nothing so like as eggs; yet no-one expects them all to taste the same. When we become sure of what will result from a particular event, it is only because we have experienced many events of that kind, all with the same effects. Now, where is that process of reasoning which infers from one instance a conclusion that was not inferred from a hundred previous instances just like this single one? I ask this for the sake of information as much as with the intention of raising difficulties. I cannot find - I cannot imagine - any such reasoning. But I am willing to learn, if anyone can teach me.

It may be said that from a number of uniform experiences we infer a connexion between the sensible qualities and the secret powers; but this seems to raise the same difficulty in different words. We still have to ask what process of argument this inference is based on. Where is the intermediate step, the interposing ideas, which join propositions that are so different from one another? It is agreed that the color, consistency and other sensible qualities of bread do not appear to be inherently connected with the secret powers of nourishment and support. If they were, we could infer these secret powers from a first encounter with those perceptible qualities, without the aid of long previous experience; and this contradicts what all philosophers believe and contradicts plain matters of fact. Start by thinking of us in our natural state of ignorance, in which we know nothing about the powers and influence of anything. How does experience cure this ignorance? All it does is to show us that certain {similar} objects had similar effects; it teaches us that those particular objects had such and such powers and forces at those particular times. When a new object with similar perceptible qualities is produced, we expect similar powers and forces and look for a similar effect. We expect for instance that stuff with the color and consistency of bread will nourish us. But this surely is a movement of the mind which needs to be explained. When a man says "I have found in all past instances such and such sensible qualities conjoined with such and such secret powers", and then goes on to say "Similar sensible qualities will always be combined with similar secret powers", he is not guilty of merely repeating himself; these propositions are in no way the same. The second proposition is inferred from the first, you may say; but you must admit that the inference is not intuitive [that is, it cannot be seen at a glance to be valid], and it is not demonstrative either [that is, it cannot be carried through by a series of steps each of which can be seen at a glance to be valid]. What kind of inference is it, then? To call it experiential is to beg the question. For all inferences from experience are based on the assumption that the future will resemble the past, and that similar powers will be combined with similar sensible qualities. As soon as the suspicion is planted that the course of nature may change, so that the past stops being a guide to the future, all experience becomes useless and cannot support any inference or conclusion. So no arguments from experience can support this resemblance of the past to the future, because all such arguments are based on the assumption of that resemblance. However regular the course of things has been, that fact on its own does not prove that the future will also be regular. It is no use your claiming to have learned the nature of bodies from your past experience. Their secret nature, and consequently all their effects and influence, may change without any change in their perceptible qualities. This happens sometimes with regard to some objects: Why may it not happen always with regard to all? What logic, what process of argument, secures you against this? You may say that I do not behave as though I had doubts about this; but that would reflect a misunderstanding of why I am raising these questions. When I am considering how to act, I am quite satisfied that the future will be like the past; but as a philosopher with an inquiring - I will not sceptical - turn of mind, I want to know what this confidence is based upon. No reading or enquiry has yet been able to remove my difficulty. Can I do better than to put the difficulty before the public, even though I may not have much hope of being given a solution? In this way we shall at least be aware of our ignorance, even if we do not increase our knowledge.

It would be inexcusably arrogant to conclude that because I have not discovered a certain argument it does not really exist. Even if learned men down the centuries have searched for something without finding it, perhaps it would still be rash to conclude with confidence that the subject must surpass human understanding. Even though we examine all the sources of our knowledge and conclude that they are unfit for a given subject, we may still suspect that the list of sources is not complete or our examination of them not accurate. With regard to our present subject, however, there are reasons to think that my conclusion is certainly right and that I am not arrogant in thinking so.

It is certain that the most ignorant and stupid peasants, even infants, indeed even brute beasts, improve by experience and learn the qualities of natural objects by observing their effects. When a child has felt pain from touching the flame of a candle, he will be careful not to put his hand near any candle, and will expect a similar effect from any cause which is similar in its appearance. If you assert that the child's understanding comes to this conclusion through a process of argument, it is fair for me to demand that you produce that argument, and you have no excuse for refusing to comply. You cannot say that the argument has eluded you because it is so difficult and complex, because you have said that a mere infant finds it easy! So if you hesitate for a moment, or if after reflection you produce any intricate or profound argument, you have in effect given up your side in this dispute: you have as good as admitted that it is not reasoning which leads us to suppose the future to resemble the past and to expect similar effects from apparently similar causes. This is the proposition which I intended to establish in the present section. If I am right about it, I do not claim it as any great discovery. If I am wrong, then there is an argument {from past to future} which was perfectly familiar to me long before I was out of my cradle, yet now I cannot discover it. What a backward scholar I must be!

The passion for philosophy, like that for religion, involves a certain danger. Although it aims to correct our behavior and wipe out our vices, it may - through not being handled properly - end up by merely encouraging us to carry on in directions which we are already naturally inclined to follow. We may set out to achieve philosophical wisdom and firmness, and to become satisfied with the pleasures of the mind {as distinct from those of the body}, yet reason ourselves out of all virtue as well as all social enjoyment, ending up with a philosophy which (like that of Epictetus and other Stoics) is only a more refined system of selfishness. While we meditate on the vanity of human life, and focus our thoughts on the empty and transitory nature of riches and honours, perhaps we are really just finding excuses for our idleness, trying to get reason's support for our lazy unwillingness to be busy in the world. However, one kind of philosophy seems to run little risk of this drawback, because it does not join forces with any disorderly passion of the human mind, and cannot get mixed up with any of our natural tendencies or inclinations; and that is the sceptical philosophy. The sceptics always talk of doubt and suspending judgment, of the danger of deciding too quickly, of keeping intellectual inquiries within narrow limits, and of giving up all theorizing that is not in touch with common life and practice. So their philosophy is as opposed as it could be to the mind's idleness, its rash arrogance, its grandiose claims, and its superstitious credulity. This philosophy has a humbling effect on every passion except the love of truth; and that could never be carried too far. Given that this philosophy is almost always harmless and innocent, it is surprising that it should so often be criticized and stigmatized as libertine, profane, and irreligious. Perhaps the very feature that makes it so innocent also brings hatred and resentment against it. It does not encourage any vices or bad habits, so it has few supporters; but it does oppose many vices and follies, which is why it has so many enemies.

When it tries to limit our enquiries to common life, this philosophy does not run any risk of going too far and undermining the reasonings that we use in common life, pushing its doubts so far as to destroy all action and belief. Nature will always maintain its rights, and prevail in the end over any abstract reasoning whatsoever. {That is, we shall continue to think and act in the ways that our human nature dictates - the ways that are natural to us - and there is no chance of our being deflected from these by philosophical considerations.} For example, I showed in the preceding section that whenever we reason from experience we take a step which is not supported by any argument or intellectual considerations; but these experiential reasonings are the basis for almost all the knowledge that we have, and there is no chance of their being dislodged by the discovery that they cannot be justified by arguments. If we are not led by argument to make inferences from past experience, we must be led by something else that is just as powerful - some other principle which will have power in our lives as long as human nature remains the same. It would be worthwhile to explore what that other principle is.

Suppose that a highly intelligent and thoughtful person were suddenly brought into this world; he would immediately observe one event following another, but that is all he could discover. He would not be able by any reasoning to reach the idea of cause and effect, because (firstly) the particular powers by which all natural operations are performed are never perceived through the senses, and (secondly) there is no reason to conclude that one event causes another merely because it precedes it. Their occurring together may be arbitrary and casual, with no causal connection between them. In short, until such a person had more experience he could never reason about any matter of fact, or be sure of anything beyond what was immediately present to his memory and senses.

Now suppose that our person gains more experience, and lives long enough in the world to observe similar objects or events occurring together constantly; now what conclusion does he draw from this experience? He immediately infers the existence of one object from the appearance of the other! Yet all his experience has not given him any idea or knowledge of the secret power by which one object produces another; nor can any process of reasoning have led him to draw this inference. But he finds that he cannot help drawing it: and he will not be swayed from this even if he becomes convinced that there is no intellectual support for the inference. Some other principle is at work, compelling him to go through with it.

This principle is Custom or Habit. When we are inclined to behave or think in some way, not because it can be justified by reasoning or some process of the understanding but just because we have behaved or thought like that so often in the past, we always say that this inclination is the effect of "Custom". In using that word we do not claim to give the basic reason for the inclination. All we are doing is to point out a fundamental feature of human nature which everyone agrees is there, and which is well known by its effects. Perhaps that is as far as we can go. Perhaps, that is, we cannot discover the cause of this cause, and must rest content with it as the deepest we can go in explaining our conclusions from experience. Our ability to go that far should satisfy us; we ought not to complain about the narrowness of our faculties because they will let us dig deeper. We do at least have here a very intelligible proposition and perhaps a true one: After the constant conjunction of two objects - heat and flame, for instance, or weight and solidity - sheer hsbit makes us expect the one when we experience the other. Indeed, this hypothesis seems to be the only one that could explain why we draw from a thousand instances an inference which we cannot draw from a single one that is exactly like each of the thousand. Reason is not like that. The conclusions it draws from considering one circle are the same as it would form after surveying all the circles in the universe. But no man, having seen only one body move after being pushed by another, could infer that every other body will move after a similar collision. All inferences from experience, therefore, are effects of custom and not of reasoning.

<Footnote: Writers often distinguish between reason and experience, and suppose that these kinds of argumentation are entirely different from each other. The arguments of reasons are thought to result purely from our intellectual faculties, which establish principles of science and philosophy by considering a priori the nature of things, examining the effects that must follow from their operation. The arguments from experience are supposed to be derived entirely from sense and observation, through which we learn what has actually resulted from the operation of particular objects and from this can infer what their results will be in the future. Thus, for instance, the limitations and restraints of civil government and a legal constitution may be defended either from reason which - reflecting on the great frailty and corruption of human nature - teaches that no man can safely be trusted with unlimited authority; or from experience and history, which inform us of the enormous abuses that have resulted in every age and country from an excess of such authority.

The same distinction between reason and experience is maintained in all our discussions about the conduct of life. While the experienced statesman, general, physician, or merchant is trusted and followed, the unpracticed novice, however talented he may be, is neglected and despised. Reason can enable one to make plausible estimates of what will be likely to ensue from such and such conduct in such and such circumstances, people say, but they regard reason as not good enough unless it gets help from experience. Only experience (they hold) can give stability and certainty to the results that are reached {by reason} from study and reflection.

However, although this distinction is universally accepted, both in practical life and in intellectual inquiry, I do not hesitate to say that it is basically mistaken, or at least superficial.

If we examine (i) arguments of the kinds I have mentioned which are supposed to involve nothing but reasoning and reflection, they turn out to be ultimately based on some general principle or conclusion for which we have no reason but observation and experience. The only difference between them and (ii) the maxims which are commonly thought to come from pure experience is that (i) cannot be established without some process of thought - some reflection on what we have observed, in order to sort out its details and trace its consequences - whereas in (ii) the experienced event is exactly like the one we predict on the new occasion. Consider the fear that if our monarchs were freed from the restraints of laws they would become tyrants. We might arrive at this fear in either of two ways: (ii) through our knowledge of the history of Tiberius or Nero; (i) through our experience of fraud or cruelty in private life, which with a little thought we can take as evidence of the general corruption of human nature and of the danger of putting too much trust in mankind. In each case the ultimate basis for the fear that we arrive at is experience.

Any man, however young and inexperienced, will have been led by his experience to many general truths about human affairs and the conduct of life; but he will be apt to go wrong in putting them into practice, until time and further experience have broadened the scope of these truths and taught him how to apply them. Talented though he may be, he will be likely to overlook some apparently minor aspects of a situation which are in fact crucial to the conclusions he ought to draw and to how he ought to act. The truth is that an "unexperienced reasoner" could not reason at all if he had really had no experience; and when we apply that phrase to anyone, we mean it only in a comparative sense - meaning by "unexperienced reasoner" someone who has not had much experience. End of footnote.>

Custom, then, is the great guide of human life. It alone is what makes our experience useful to us, and makes us expect future sequences of events to be like ones that have appeared in the past. Without the influence of custom, we would be entirely ignorant of every matter of fact beyond what is immediately present to the memory and senses. We would never know what means we should adopt in order to reach our ends; we could not employ our natural powers to produce any desired effect. There would be an end of all action and of most theorizing.

I should point out, however, that although our inferences from experience carry us beyond our memory and senses, and assure us of matters of fact which happened in distant places and at remote times, any such inference must start with a fact that is present to the senses or memory. A man who found in a desert country the remains of magnificent buildings would conclude that the country had long before had civilized inhabitants; but without the initial experience he could never infer this. We learn the events of bygone ages from history; but to do this we must read the books which give the information, and carry out inferences from one report to another, until finally we arrive at the eye-witnesses and spectators of these distant events. In short, if we did not start with some fact that is present to the memory or senses, our reasonings would be merely hypothetical; and however strong the particular links might be, the whole chain of inferences would have nothing to support it, and we could not use it to arrive at the knowledge of any real existence. If I ask why you believe any particular matter of fact which you tell me of, you must tell me some reason; and this reason will be some other fact connected with it. But you cannot go on like this for ever: eventually you must end up with some fact that is present to your memory or senses - or else admit that your belief has no foundation at all.

What are we to conclude from all this? Something that is far removed from the common theories of philosophy, yet is very simple:

All beliefs about matters of fact or real existence are derived merely from something that is present to the memory or senses, and a customary association of that with some other thing.

We have looked at every possible source for an idea of power or necessary connexion, and have found nothing. [That occurs in Part I of this section, not included in these readings.] However hard we look at an isolated physical episode, it seems, we can never discover anything but one event following another; we never find any force or power by which the cause operates, or any connexion between it and its supposed effect. The same holds for the influence of mind on body: the mind wills, and then the body moves, and we observe both events; but we do not observe - and cannot even conceive - the tie which binds the volition to the motion, that is, the energy by which the mind causes the body to move. And the power of the will over its own faculties and ideas {- that is, over the mind, as distinct from the body -} is no more comprehensible. Summing up, then: throughout the whole of nature there seems not to be any one instance of connexion that is conceivable by us. All events seem to be entirely loose and separate. One event follows another, but we never can observe any tie between them. They seem associated, but never connected. And as we can have no idea of anything which never appeared {as an impression} to our outward sense or inward feeling, we are forced to conclude that we have no idea of "connexion" or "power" at all, and that those words - as used in philosophical reasonings or in common life - have absolutely no meaning.

One escape route may be still open to us: there is one possible source for the idea of connexion or power which we have not yet examined. When we are confronted by any natural object or event of which we have had no experience, no amount of cleverness and hard work will enable us to discover or even guess what event will result from it, or to make any prediction that goes beyond what is immediately present to our memory and senses. Even after we know from experience what the result was in a particular case, we are not entitled to bring it under a general rule, or to predict what will happen in similar cases in the future. Basing a view about the whole course of nature on a single experiment, however accurate or certain it may be, is rightly thought to be too bold. But if events of one kind have always in all instances been associated with events of some one other kind, we no longer shrink from predicting an event of the latter kind when we experience one of the former kind. We then call one the Cause, and the other the Effect. We suppose there to be some connexion between them; some power in the cause by which it infallibly produces the effect, operating with the greatest certainty and strongest necessity.

The source of this idea of a necessary connexion among events seems to be a number of similar instances of the regular pairing of events of these two kinds; and the idea cannot be prompted by any one of these instances on its own, however comprehensively we examine it. But what can a number of instances contain that is different from any single instance which is supposed to be exactly like them? Only that when the mind experiences many similar instances, it acquires a habit of expectation: the repetition of the pattern affects it in such a way that when it observes an event of one of the two kinds it expects an event of the other kind to follow. So the feeling or impression from which we derive our idea of power or necessary connexion is a feeling of connexion in the mind - a feeling that accompanies the imagination's habitual move from observing one event to expecting another of the kind that usually follows it. That is all there is to it. Study the topic from all angles; you will never find any other origin for that idea. This is the only difference between a single instance (which can never give us the idea of connexion) and a number of similar instances (which do suggest the idea). The first time a man saw motion being passed from one thing to another in a collision, as when one billiard ball hits another, he could not say that the red ball's starting to move was connected with the white ball's hitting it, but only that one event followed the other. After seeing several instances of this kind, he then says that they {- that is, the two events within each instance -} are connected. What has happened to give rise to this new idea of connexion? Only that he now feels these events to be connected in his imagination, and can predict the occurrence of one from the appearance of the other. So when we say that one event is connected with another, all we mean is that they have come to be connected in our thought so that we are willing to conduct this inference through which they are taken to be proofs of each other's existence. This is a strange conclusion! But it seems to be well supported by the evidence. Even people who are in a general way cautious about what the understanding can achieve, or sceptical about every conclusion which is new and extraordinary, should not on that account be suspicious of this conclusion. It announces a discovery concerning the weakness and narrow limits of human reason and capacity - nothing could be more agreeable to scepticism than it is.

And what stronger example than this could we find of how surprisingly ignorant and weak our understanding is? If there is any relation between objects which it matters to us to know perfectly, it is that of cause and effect. It is the basis for all our reasonings about matters of fact or existence; it alone assures us about objects which are not now present to memory or senses. The only immediate use of all the sciences is to teach us how to control and regulate future events through their causes. So our thoughts and enquiries are at every moment concerned with the relation of cause to effect; yet our ideas regarding it are so imperfect that we cannot accurately define "cause" except in terms of something that is extraneous to the cause, forming no part of it. {There are two ways of doing this.} (1) Similar events are always associated with similar. Of this we have experience. Suitably to this experience, therefore, we may define a "cause" to be an event followed by another, where all events similar to the first are followed by events similar to the second. Or in other words where if the first event had not occurred the second would not have occurred either. [Hume states all this in terms of the "existence" of "objects" rather than the occurrence of events.] (2) The appearance of a cause always conveys the mind - in a transition brought about through custom - to the idea of the effect. Of this also we have experience. We could embody this experience in another definition of "cause": an event followed by another, where the appearance of the former always conveys the thought to the latter. Each of these definitions brings in something that lies right outside the cause itself {because definition (1) brings in earlier events similar to the cause, while (2) brings in events in the mind of the speaker}; but there is no remedy for this drawback. We cannot replace those definitions by a more perfect one which picks out something in the cause itself that connects it with its effect. We have no idea of this connexion; nor even any clear notion what we are aiming at when we try to form a conception of it. When we say, for instance, that the vibration of this string is "the cause of" this particular sound, what do we mean? We mean that this vibration is followed by this sound and either that all similar vibrations have been followed by similar sounds or that when the mind sees the vibration it immediately forms an anticipatory idea of the sound. We can look at the cause-effect relation in either of these two ways; but beyond them we have no idea of it.

<Footnote: According to these explanations and definitions, the idea of power is as relative as the idea of cause is. Each refers to an effect, or some other event constantly associated with the former. When we consider the unknown nature of an object which fixes what effects it will have, we call that its "power"; which is why everyone agrees that a thing's effects provide a measure of its power. But if they had any idea of power as it is in itself, why could they not measure it in itself?

It is true that the words "force", "power", "energy" &c. occur frequently throughout everyday conversation as well as in philosophy; but that is no proof that we are ever acquainted with the connecting principle between cause and effect, or that we can account ultimately for one event's causing another. These words, as commonly used, have very loose meanings, and their ideas {- that is, the associated ideas which give them their meanings -} are very uncertain and confused. {Those ideas fall into two groups, each of which is animistic, treating inanimate causes and effects as though they were alive. (i) One group of ideas comes into play only when a cause-effect transaction is thought of as involving a transfer of motion from one object to another. (ii) The other group are the ideas that are treated in my account of causal reasoning.} (i) No animal can set external bodies into motion without a feeling of effort; and every animal knows the feeling of being pushed or hit by a moving external object. These sensations - which are merely animal, and from which we can a priori draw no conclusions - we are inclined to transfer to inanimate objects, and to suppose that they have some such feelings whenever motion is transferred by them or to them. {For example, we suppose or pretend that the white billiard ball exerts an effort which it feels, and that the red one feels the impact of the white one.} (ii) When one event causes another and we do not bring the thought of motion-transfer into play, {we have no way of bringing in the ideas based on the feelings of pushing or being pushed, and so} we take into account only the constant experienced association of the two kinds of events. That has set up in our minds a habitual connexion between our ideas of the two events, and we transfer the feeling of that mental connexion to the objects. We attribute to external bodies internal sensations which they induce in us; this is absolutely normal human practice. [In another of his works, Hume writes: "The mind has a great propensity to spread itself on external objects, and to conjoin with them any internal impressions which they occasion...".] End of footnote.>

To sum up the reasonings of this section: Every idea is copied from a previous impression or feeling, and where we cannot find any impression we may be certain that there is no idea. No isolated episode of mental or physical causation yields any impression of power or necessary connexion. Therefore, no such episode can prompt us to form any idea of power or necessary connexion. When many similar episodes are observed to occur, however, and events of one kind are always followed events of a second kind, we then start to form the notion of cause and connexion. The experience of this regularity gives us a new impression, namely {the feeling or impression of} a custom-induced connexion in our thought or imagination between one event and another; and the idea that we have been hunting for {- the idea of power or necessary connexion -} is copied from this impression. {Here is why this must be right.} The idea arises from a series of similar episodes and not from any one taken singly; so it must arise from whatever it is that differentiates the series from each individual episode; and the only difference is this customary connexion or transition of the imagination. In every other respect, each individual episode is just like the whole series. To return to our humdrum example: The first time we saw motion being transferred through a collision between two billiard balls, what we saw was exactly like any other such collision that we might see now; the only difference was that on that first occasion we could not infer one event from the other, as we can now after such a long course of uniform experience. I not know whether the reader will easily grasp this reasoning. I am afraid that if I were to go on longer about it, presenting it from a greater variety of angles, it would only become more obscure and complicated.

Philosophical arguments proving the existence of a Deity and refuting the fallacies of Atheists outnumber the arguments on any other topic. Yet the most religious philosophers still disagree about whether any man can be so blinded as to be an atheist. How shall we reconcile these contradictions? The knights-errant who wandered about to clear the world of dragons and giants never had the least doubt that these monsters existed!

The Sceptic is another enemy of religion who naturally arouses the indignation of all religious authorities and more solemn philosophers; yet it is certain that nobody ever met such an absurd creature {as a sceptic}, or talked with a man who had no opinion on any subject, practical or theoretical. So the question naturally arises: What is meant by "sceptic"? And how far it is possible to push these philosophical principles of doubt and uncertainty?

Descartes and others have strongly recommended one kind of scepticism, to be practised in advance of philosophy or any other studies. It preserves us, they say, against error and rash judgment. It recommends that we should doubt not only all our former opinions and principles but also our very faculties. The reliability of our faculties, these philosophers say, is something we must be assured of by a chain of reasoning, deduced from some first principle which cannot possibly be fallacious or deceitful. But there is no such first principle which has an authority above others that are self-evident and convincing. And even if there were one, we could not advance a step beyond it except by using those very faculties which we are supposed to be calling into question. Cartesian doubt, therefore, if someone could attain to it (as it plainly nobody could), would be entirely incurable, and no reasoning could ever bring us to confident beliefs about anything.

However, a more moderate degree of such scepticism can be quite reasonable, and is a necessary preparation for the study of philosophy: it makes us impartial in our judgments and weans our minds from prejudices which we may have arrived at thoughtlessly or taken in through education. If we

--begin with clear and self-evident principles,

--move forward cautiously, getting a secure footing at each step, and

---check our conclusions frequently, and carefully examine their consequences,

we shall move slowly, and not get far; but these are the only methods by which we can hope ever to establish conclusions which we are sure are true and which will last.

Another kind of scepticism has arisen out of scientific inquiries which are supposed to have shown that human mental faculties are either absolutely deceitful or unfit to reach fixed conclusions about any of the puzzling topics on which they are commonly employed. Even our senses are questioned by a certain kind of philosopher; and the maxims of everyday life are subjected to the same doubt as are the deepest principles of metaphysics and theology. Some philosophers accept these paradoxical tenets (if they may be called tenets), while many others try to refute them; so it is natural for us to wonder about them, and to look for the arguments on which they may be based.

I need not dwell on the well-worn arguments that sceptics have used down the ages to discredit the senses, such as the arguments drawn from the untrustworthy nature of our sense organs, which very often lead us astray: the crooked appearance of an oar half in water, the different ways an object can look depending on how far away it is, the double images which arise from pressing one eye, and many other such phenomena. These sceptical points serve only to prove that the senses, taken on their own, should not automatically be trusted, and that if they are to serve as criteria of truth and falsehood we must adjust the answers they give us by bringing reason to bear on facts about the nature of the medium {e.g. the water through which we see the lower half of the oar}, the distance of the object, and the condition of the sense organ. But other arguments against the senses go deeper, and are harder to meet.

It seems clear that we humans are naturally, instinctively inclined to trust our senses, and that without any reasoning - indeed, almost before the use of reason - we take it that there is an external universe which does not depend on our perceiving it and would have existed if there had never been any perceiving creatures or if we had all been annihilated. Even the animals are governed by a similar opinion, and maintain this belief in external objects in all their thoughts, plans and actions.

It also seems clear that when men follow this blind and powerful instinct of nature they always suppose that the very images which their senses present to them are the external objects which they perceive; it never crosses their minds that the one are merely representations of the other. This very table which we see as white and feel as hard is believed to exist independently of our perception, and to be something external to our mind, which perceives it. Our presence does not bring it into existence, and our absence does not annihilate it. It stays in existence (we think), complete and unchanging, independent of any facts about intelligent beings who perceive or think about it.

But the slightest philosophy is enough to destroy this basic belief that all men have. For philosophy teaches us that images (or perceptions) are the only things that can ever be present to the mind, and that the senses serve only to bring these images before the mind and cannot put our minds into any immediate relation with external objects. The table that we see seems to shrink as we move away from it; but the real table which exists independently of us does not alter; so what was present to the mind was not the real table but only an image of it. These are the obvious dictates of reason; and no-one who thinks about it has ever doubted that when we say "this house" and "that tree" the things we are referring to are nothing but perceptions in the mind - fleeting copies or representations of other things which are independent of us and do not change.

To that extent, then, reason compels us to contradict or depart from the basic instincts of nature, and to adopt a new set of views about the evidence of our senses. {These views amount to a philosophical system according to which (i) we perceive only images, not external objects, but (ii) there are external objects, and images represent them.} But when philosophy tries to justify this new system, and put to rest the carping objections of the sceptics, it finds itself in an awkward position {regarding the claim (ii) that there are external objects which our images represent}. Philosophy can no longer rely on the idea that natural instincts are infallible and irresistible, for those instincts led us to a quite different system which is admitted to be fallible and even wrong. And to justify {the external-object part of} this purported philosophical system by a chain of clear and convincing argument - or even any appearance of argument - is more than anyone can do.

By what argument can it be proved that the perceptions of the mind must be caused by external objects which are perfectly distinct from them and yet similar to them (if that were possible), rather than arising from the energy of the mind itself, or from the activities of some invisible and unknown spirit, or from some other cause still more unknown to us? It is admitted that many of these perceptions - e.g. in dreams, madness, and other diseases - do not in fact arise from anything external{, so how could we prove that any of them do arise from something external?}. In any case, we are utterly unable to explain how body could so act upon mind as to convey an image of itself to a mental substance which is supposed to be so different - even contrary - in its nature from the body.

Are the perceptions of the senses produced by external objects which resemble them? This is a question of fact. Where shall we look for an answer to it? To experience, surely, as we do with all other questions of that kind. But here experience is and must be entirely silent. The mind never has anything present to it except the perceptions, and cannot possibly experience their connexion with objects. The belief in such a connexion, therefore, has no foundation in reasoning {because the reasoning would have to start from something known through experience}.

We might try to prove that our senses are truthful by appealing to the truthfulness of God, but that would be a strange direction for the argument to take{, for two reasons}. (i) If the fallibility of our senses implied that God is untruthful, then our senses would never mislead us; because it is not possible that God should ever deceive. (ii) Anyway, once the external world has been called in question we are left with no arguments to prove that God exists or to show what his attributes are.

The deeper and more philosophical sceptics, trying to cast doubt on all subjects of human knowledge and enquiry, will always triumph when it comes to the question of external bodies. "Do you follow your natural instincts and inclinations," they may say, "when you affirm the truthfulness of your senses? But those instincts lead you to believe that the perception or image that you experience is itself the external object. Do you reject that view, in order to accept the more reasonable opinion that perceptions are only representations of something external? In that case you are departing from your natural inclinations and more obvious opinions; and yet you still cannot satisfy your reason, which can never find any convincing argument from experience to prove that your perceptions are connected with external objects."

Another sceptical topic - somewhat like that one - has deep philosophical roots, and might be worth attending to if there were any point in digging that far down in order to discover arguments that can be of so little serious use. All modern inquirers agree that all the sensible qualities of objects - such as hard, soft, hot, cold, white, black, &c. - are merely secondary; they do not exist in the objects themselves (it is believed), and are perceptions of the mind with no external archetype or model which they represent. If this is granted regarding secondary qualities, it also holds for the supposed primary qualities of extension and solidity, which are no more entitled to be called "primary" than the others are. The idea of extension comes purely from the senses of sight and touch; and if all the qualities that are perceived by the senses are in the mind rather than in the object, that must hold also for the idea of extension, which wholly depends on sensible ideas, that is, the ideas of secondary qualities. {To see that something is extended, you have to see colours; to feel that it is extended, you have to feel hardness or softness.} The only escape from this conclusion is to assert that we get the ideas of those "primary" qualities through abstraction; but the doctrine of abstraction turns out under careful scrutiny to be unintelligible, and even absurd. An extension that is neither tangible nor visible cannot possibly be conceived; and a tangible or visible extension which is neither hard nor soft, black nor white, is equally beyond the reach of human conception. Let anyone try to conceive a triangle in general, which has no particular length or proportion of sides, and he will soon see the absurdity of all the scholastic notions concerning abstraction and general ideas.
 

<Footnote: This argument is drawn from Dr. Berkeley; and indeed most of the writings of that able author form the best lessons of scepticism which are to be found either among the ancient or modern philosophers. Yet on his title-page he claims, no doubt sincerely, to have composed his book against the sceptics as well as against atheists and free-thinkers. But though his arguments are otherwise intended, they are all in fact merely sceptical. This is shown by the fact that they cannot be answered yet do not convince. Their only effect is to cause that momentary bewilderment and confusion which is the result of scepticism.>
 

Thus the first philosophical objection to the belief in external objects consists in this: If the belief is based on natural instinct it is contrary to reason; and if it is attributed to reason it is contrary to natural instinct, and anyway is not supported by any rational evidence that would convince an impartial person who thought about it. The second objection goes further and represents this belief as contrary to reason - at least if reason says that all sensible qualities are in the mind and not in the object. Deprive matter of all its intelligible qualities, both primary and secondary, and you in a way annihilate it and leave only a certain unknown mysterious something as the cause of our perceptions, a notion so imperfect that no sceptic will think it worthwhile to argue against it.

There may seem to be something wild about the sceptics' attempt to destroy reason by argument and reasoning; yet is that is what all their enquiries and disputes amount to. They try to find objections both to our abstract reasonings and to reasonings about matter of fact and existence.

The chief objection to abstract reasonings comes from the ideas of space and time. Those ideas, when viewed carelessly as we view them in everyday life, are very clear and intelligible; but when we look into them more closely they turn out to involve principles which seem full of absurdity and contradiction. No priestly dogmas, invented on purpose to tame and subdue the rebellious reason of mankind, ever shocked common sense more than the doctrine of the infinite divisibility of extension, with its consequences which are ceremoniously paraded by geometricians and metaphysicians as though they were something to be proud of. A real quantity which is infinitely less than any finite quantity, and containing quantities which are infinitely less than itself, and so on to infinity - this bold, enormous edifice is too weighty to be supported by any demonstration, because it offends against the clearest and most natural principles of human reason. <Footnote: Whatever disputes there may be about mathematical points, we must allow that there are physical points - that is, parts of extension which cannot be divided or lessened either by the eye or imagination. So these images which are present to the imagination or the senses are absolutely indivisible, and consequently must be regarded by mathematicians as infinitely less than any real part of extension; yet nothing appears more certain to reason than that an infinite number of them composes an infinite extension. This holds with even more force of an infinite number of those infinitely small parts of extension which are still supposed to be themselves infinitely divisible.> But what renders the matter more extraordinary is that these seemingly absurd opinions are supported by a chain of reasoning which seems clear and utterly natural, and we cannot accept the premises without accepting the conclusions. The geometrical proofs regarding the properties of circles and triangles are as convincing and satisfactory as they could possibly be; but if we accept them, how can we deny that the angle of contact between any circle and its tangent is infinitely less than any angle between straight lines, and that as the circle gets larger the angle of contact becomes still smaller, ad infinitum? The demonstration of these principles seems as flawless as the one proving that the three angles of a triangle equal 180, though the latter conclusion is natural and easy while the former is pregnant with contradiction and absurdity. Reason here seems to be thrown into a kind of bewilderment and indecision which, without prompting from any sceptic, makes it unsure of itself and of the ground it walks on. It sees a bright light which illuminates some places; but right next to them there is the most profound darkness. Caught between these, reason is so dazzled and confused that there is hardly any topic on which it can reach a confident conclusion.

The absurdity of these bold conclusions of the abstract sciences seems to become even more conspicuous with regard to time than it is concerning extension. An infinite number of real parts of time, passing in succession and gone through one after another - this appears to be such an obvious contradiction that nobody, one would think, could bring himself to believe it unless his judgment had been corrupted, rather than being improved, by the sciences.

Yet still reason must remain restless and unquiet, even with regard to the scepticism it is driven to by these seeming absurdities and contradictions. We cannot make sense of the thought that a clear, distinct idea might contain something that is contradictory to itself or to some other clear, distinct idea; this is indeed as absurd a proposition as we can think of. So this scepticism concerning some of the paradoxical conclusions of mathematics {- a scepticism which implies that some of our clear, distinct ideas contradict others -} is itself something we must be sceptical about, approaching it in a doubting, hesitant frame of mind.
 

<Footnote: We might be able to avoid these absurdities and contradictions if we admitted that there is no such thing as abstract or general ideas, properly speaking; but that all general ideas are really particular ones attached to a general term which brings to mind other particular ideas which in some way resemble the idea that is present to the mind. Thus when the word "horse" is pronounced, we immediately form the idea of a black or a white animal of a particular size and shape; but as that word is also usually applied to animals of other colours, figures and sizes, these ideas are easily recalled even when they are not actually present to the imagination; so that our reasoning can proceed in the same way as if they were actually present. If this is admitted - and it seems reasonable - it follows that the ideas of quantity which mathematicians reason with are particular ones, that is, ideas of the kind that come through the senses and imagination; in which case those ideas cannot be infinitely divisible. At this point I merely drop that hint, without developing it in detail. It does seem to be the readiest solution for these difficulties. We need some solution if the mathematicians are not to be exposed to the ridicule and contempt of ignorant people.>
 

Sceptical objections to reasonings about matters of fact are of two kinds - (i) everyday informal objections, and (ii) philosophical ones. (i) The informal objections are based on the natural weakness of human understanding, the contradictory opinions which have been held at different times and in different countries, the variations of our judgment in sickness and health, youth and old age, prosperity and adversity, the perpetual differences of opinion between different individuals - and many other considerations of that kind, but there is no need to go on about them. These objections are weak. For as in ordinary life we reason every moment regarding fact and existence, and cannot survive without continually doing so, no objections that are based on this procedure can be sufficient to undermine it. The great subverter of excessive scepticism is action, practical projects, the occupations of everyday life. Sceptical principles may flourish and triumph in the philosophy lecture room, where it is indeed hard if not impossible to refute them. But as soon as they come out of the shadows, are confronted by the real things that our beliefs and emotions are addressed to, and thereby come into conflict with the more powerful principles of our nature, sceptical principles vanish like smoke and leave the most determined sceptic in the same {believing} condition as other mortals.

(ii) The sceptic, therefore, had better stay in the area where he does best, and present the philosophical objections whose roots run deeper {than the facts on which the informal objections are based}. These seem to provide him with plenty of victories. He can rightly insist

--that all our evidence for any matter of fact which lies beyond the testimony of sense or memory is entirely based on the relation of cause and effect;

--that our only idea of this relation is the idea of two kinds of event which have frequently been associated with one another;

--that we have no argument to convince us that kinds of event which we have often found to be associated in the past will be so in future;

--and that what leads us to this inference is merely custom - a certain instinct of our nature - which it is indeed hard to resist but which like any other instinct may be wrong and deceitful.

While the sceptic presses these points, he is in a strong position, and seems to destroy all assurance and conviction, at least for a while. (In a way, what he is showing is not his strength but rather his and everyone's weakness!) These arguments of his could be developed at greater length, if there were any reason to think that doing this would be useful to mankind.

That brings me to the chief and most unanswerable objection to excessive scepticism, namely that no lasting good can ever result from it while it remains in its full force and vigour. We need only ask such a sceptic: "What do you want? What do you intend to achieve through your sceptical arguments?" He is immediately at a loss, and does not know what to answer. A Copernican or Ptolemaic who supports a particular system of astronomy may hope to produce in his audience beliefs that which will remain constant and long-lasting. A Stoic or Epicurean displays principles which may not last, but which have an effect on conduct and behaviour. But a Pyrrhonian [= extreme sceptic; Pyrrho was the first great sceptic in ancient Greece] cannot expect his philosophy to have any steady influence on the mind, and if it did, he could not expect the influence to benefit society. On the contrary, if he will admit anything he must admit that if his principles were universally and steadily accepted, all human life would come to an end. All discourse and all action would immediately cease; and men would remain in a total lethargy until their miserable lives came to an end through lack of food, drink and shelter. It is true that this fatal outcome is not something we really have to fear: nature is always too strong for principle. And though a Pyrrhonian may throw himself or others into a momentary bewilderment and confusion by his deep arguments, the first and most trivial event in life will put all his doubts and worries to flight, and will leave him - in every aspect of his actions and beliefs - in just the same position as any other kind of philosopher, and indeed the same as someone who had never concerned himself with philosophical researches at all. When he awakes from his dream, the sceptic will be the first to join in the laughter against himself and to admit that all his objections are mere amusement and can only serve to show how odd and freakish the situation of mankind is: we must act and reason and believe, but however hard we try we cannot find a satisfactory basis for those operations and cannot remove the objections that can be brought against them.

There is indeed a milder kind of scepticism which may be both durable and useful. It may be a part of what results from Pyrrhonism, or excessive scepticism, when its undiscriminating doubts are modified a little by common sense and reflection. Most people are naturally apt to be positive and dogmatic in their opinions; they see only one side of an issue, have no idea of any arguments going the other way, and recklessly commit themselves to the principles that seem to them right, intolerant of those who hold opposing views. Pausing to reflect, or balancing arguments pro and condition, only serves to get them muddled, to damp down their emotions, and to delay their actions. They are very uncomfortable in this state, and are thus impatient to escape from it; and they think they can keep away from it - the further the better - by the violence of their assertions and the obstinacy of their beliefs. But if these dogmatic reasoners became aware of how frail the human understanding is, even at its best and most cautious, this awareness would naturally lead to their being less dogmatic and outspoken, less sure of themselves and less prejudiced against antagonists. The illiterate may reflect on the fact that learned people, despite all their advantages of study and reflection, are often cautious and tentative in their opinions. If any of the learned should be temperamentally inclined to pride and obstinacy, a small dose of Pyrrhonism might lessen their pride by showing them that the few advantages they have over other {unlearned} men do not amount to much when compared with the universal perplexity and confusion which is inherent in human nature. There is, in short, a degree of doubt and caution and modesty which every reasoner ought to have at all times in every context of inquiry.

Another kind of moderate scepticism which may be useful to mankind, and which may be the natural result of Pyrrhonian doubts, is the limitation of our enquiries to the subjects that our narrow human understanding is best equipped to deal with. The imagination of man naturally soars into the heights: it rejoices in whatever is remote and extraordinary, and runs off uncontrollably into the most distant parts of space and time in order to avoid the familiar objects that it has become used to. A faculty of Judgment that is working properly proceeds in the opposite way: it avoids all distant and high enquiries, and confines itself to subjects that we meet with in everyday activities and experience, leaving grander topics to poets and orators or to priests and politicians. The best way for us to be brought into this healthy frame of mind is for us to become thoroughly convinced of the force of Pyrrhonian doubt, and to see that our only possible escape from it is through the strong power of natural instinct. Those who are drawn to philosophy will still continue their researches, attracted by the immediate pleasure of this activity and by their realization that philosophical doctrines are nothing but organized and corrected versions of the thoughts of everyday life. But they will never be tempted to go beyond everyday life so long as they bear in mind the imperfection - the narrowness of scope, and the inaccuracy - of their own faculties. Given that we cannot even provide a satisfactory reason why we believe after a thousand experiments that a stone will fall or fire will burn, can we ever be confident in any of our beliefs about the origin of worlds, or about the unfolding of nature from and to eternity?

The slightest inquiry into the natural powers of the human mind, and the comparison of those powers with the topics the mind studies, will be enough to make anyone willing to limit the scope of his enquiries in the way I have proposed. Let us then consider what are the proper subjects of science and enquiry.

It seems to me that the only objects of the abstract sciences - the ones whose results are rigorously proved - are quantity and number, and that it is mere sophistry and illusion to try to extend this more perfect sort of knowledge beyond these bounds. [Hume continues with a rather obscure line of thought, the conclusion of which is that in mathematics there is a role for long, strict arguments, while in other areas the only rigorous arguments we can construct are very short. That passage is omitted here.] That the square on the hypotenuse is equal to the squares of the other two sides cannot be known without a train of reasoning and enquiry. But to convince us that where there is no property there can be no injustice it is only necessary to define the terms and explain "injustice" to be "a violation of property". This proposition is indeed merely an imperfect definition. Similarly with all those purported reasonings which may be found in every other branch of learning except the sciences of quantity and number. The latter sciences, it is safe to say, are the only proper objects of knowledge and demonstration.

All other enquiries of men regard only matter of fact and existence; and these obviously cannot be demonstrated. Whatever is the case may not be the case. No negation of a fact can involve a contradiction. The nonexistence of any existing thing is as clear and distinct an idea as its existence. The proposition which affirms it not to exist, even if it is quite false, is just as conceivable and intelligible as that which affirms it to exist. The case is different with the sciences, properly so called [Hume means: the mathematical sciences]. Every mathematical proposition which is not true is confused and unintelligible. That the cube root of 64 is equal to the half of 10 is a false proposition and can never be distinctly conceived. But that Caesar never existed may be a false proposition but still it is perfectly conceivable and implies no contradiction.

It follows that the existence of any thing can only be proved by arguments from its cause or its effect; and such arguments are based entirely on experience. If we reason a priori, anything may appear able to produce anything. The falling of a pebble may, for all we know, extinguish the sun; or the wish of a man may control the planets in their orbits. Only experience teaches us the nature and limits of cause and effect, and enables us to infer the existence of one object from that of another. <Footnote: That impious maxim of the ancient philosophy, Ex nihilo, nihil fit [From nothing, nothing is made], which was supposed to rule out the creation of matter, ceases to be a secure axiom according to this philosophy. Not only might the will of the supreme Being create matter; but for all we know a priori the will of any other being might create it, or any other cause that the most fanciful imagination can assign.> Such is the foundation of factual reasoning, which forms the greater part of human knowledge and is the source of all human action and behaviour.

Factual reasonings concern either particular or general facts. Everyday practical thinking is concerned only with the former, as is the whole of history, geography and astronomy.

The sciences which treat of general facts are politics, natural philosophy [= physics], physic [= medicine], chemistry, &c. where the qualities, causes and effects of a whole species of objects are investigated.

Divinity or Theology proves the existence of a Deity and the immortality of souls, so the reasonings which compose it partly concern particular facts and partly general ones. In so far as it is supported by experience Theology has a foundation in reason, but its best and most solid foundation is faith and divine revelation.

Morals and {artistic} criticism are in the domain of taste and feeling rather than of intellectual thought. Beauty, whether moral or natural, is felt rather than perceived. If we do reason about it and try to fix standards of judgment, we must bring in facts which can be the objects of reasoning and enquiry - e.g. facts about the general taste of mankind.

When we go through libraries, convinced of these principles, what havoc must we make? If we take in our hand any volume - of divinity or school metaphysics, for instance - let us ask, Does it contain any abstract reasoning about quantity or number? No. Does it contain any experiential reasoning about matters of fact and existence? No. Then throw it in the fire, for it can contain nothing but sophistry and illusion.

Some philosophers imagine that we are every moment intimately conscious of what we call our self; that we feel its existence and its continuing to exist, and are certain - more even than any demonstration could make us - both of its perfect identity and of its simplicity. The strongest sensations and most violent emotions, they say, instead of distracting us from this view {of our self}, only focus it all the more intensely, making us think about how these sensations and emotions affect our self by bringing it pain or pleasure. To offer further evidence of the existence of one's self would make it less evident, not more, because no fact we could use as evidence is as intimately present to our consciousness as is the existence of our self. If we doubt the latter, these philosophers say, we cannot be certain of anything.

Unfortunately, all these forthright assertions are in conflict with the very experience which is supposed to support them. We do not so much as have an idea of self of the kind that is here described. From what impression could this idea be derived? This question cannot be answered without obvious contradiction and absurdity; yet it must be answered if the idea of self is to qualify as clear and intelligible. Every real idea must arise from some one impression. But self or person is not any one impression, but is rather that to which all our many impressions and ideas are supposed to be related. If the idea of self came from an impression, it would have to be an impression that remained invariably the same throughout our lives, because the self is supposed to exist in that way. But no impression is constant and invariable. Pain and pleasure, grief and joy, passions and sensations follow one other and never all exist at the same time. It cannot therefore be from any of these impressions or from any other that the idea of self is derived. So there is no such idea.

Furthermore, if we retain this hypothesis about the self, what are we to say about all our particular perceptions? They are all different, distinguishable, and separable from one other - they can be separately thought about, and can exist separately - with no need for anything to support their existence. In what way do they belong to self? How are they connected with it? For my part, when I enter look inward at what I call myself, I always stumble on some particular perception of heat or cold, light or shade, love or hatred, pain or pleasure, or the like. I never catch myself without a perception, and never observe anything but the perception. When I am without perceptions for a while, as in sound sleep, for that period I am not aware of myself and can truly be said not to exist. If all my perceptions were removed by death, and I could not think, feel, see, love or hate after my body had decayed, I would be entirely annihilated - I cannot see that anything else would be needed to turn me into nothing. If anyone seriously and thoughtfully claims to have a different notion of himself, I cannot reason with him any longer. I have to admit that he may be right about himself, as I am about myself. He may perceive something simple and continued which he calls himself, though I am certain there is no such thing in me.

But setting aside metaphysicians of this kind, I am willing to affirm of the rest of mankind that they are nothing but a bundle or collection of different perceptions which follow each other enormously quickly and are in a perpetual flux and movement. Our eyes cannot turn in their sockets without varying our perceptions; our thought is still more variable than our sight; and all our other senses and faculties contribute to this change in our perceptions, with no one of them remaining unaltered for a moment. The mind is a kind of stage on which many perceptions successively make their appearance: they pass back and forth, glide away, and mingle in an infinite variety of positions and situations. Strictly speaking, there is no simplicity in the mind at one time and no identity through different times, no matter what natural inclination we may have to imagine that simplicity and identity. {That is to say: It is not strictly true that when a blue colour is seen and a whistling sound heard at the same time, one single unified mind has both these perceptions; nor is it strictly true that the mind which has a certain perception at one time is the very same mind that has a perception at another time.} The "stage" comparison must not mislead us. What constitutes the mind is just the successive perceptions; we have not the faintest conception of the place where these scenes are represented or of the materials of which it is composed.

What, then, makes us so inclined to ascribe an identity to these successive perceptions, and to suppose that we have an invariable and uninterrupted existence through the whole course of our lives? To answer this question we must distinguish what we think and imagine about personal identity from the role of personal identity in our emotions and desires. The former is our present subject. To explain it perfectly we must dig fairly deep: first we must account for that identity which we attribute to plants and animals, because there is a great analogy between that and the identity of a self or person.

We have a clear idea of an object that remains invariable and uninterrupted while time supposedly passes. We call this the idea of identity or sameness. We have also a clear idea of many different objects existing successively in a close relation to one another; and this, properly understood, is just as good an example of diversity as it would be if the objects were not related to one another in any way. {As the sand runs in the hour-glass, this grain is distinct from that one which falls a tenth of a second later and a micromillimetre behind; they are diverse from one another, which is simply to say that they are two grains, not one; and the fact that they are closely related to one another (in space, in time, and in being alike) makes no difference to that. They are as distinct from one another - they are as clearly two - as the Taj Mahal and the Grand Canyon.} But though these two ideas of identity and a sequence of related objects are perfectly distinct from one another and even contrary, yet in our everyday thinking they are often confused with one another, treated as though they were the same. {I now explain what leads us into that confusion.} Here are two mental activities:

(i) thinking about a sequence of related objects, and

(ii) thinking about one uninterrupted and invariable object.

Although these are distinct, and involve different activities of the imagination, they feel the same. The activity in (i) does not require much more effort than the activity in (ii): in (i) the relation between the objects helps the mind to move easily from one to the next, making its mental journey as smooth as if it were contemplating one continued object as in (ii). This resemblance between these two kinds of thought generates the confusion in which we mistakenly substitute the notion of (ii) identity for that of (i) related objects. When contemplating a sequence of related objects, at one moment we think of it as (i) variable or interrupted, {which it is,} yet the very next moment we {wrongly} think of it as (ii) a single, identical, unchanging and uninterrupted thing. {That completes the explanation.} The resemblance that I have mentioned {between the two acts of the mind} gives us such a strong tendency to make this mistake that we make it without being aware of what we are doing; and though we repeatedly correct ourselves and return to a more accurate and philosophical way of thinking, we cannot keep this up for long, and we fall back once more into the mistake. Our only way out {of this oscillation between truth and error} is to give in to the error and boldly assert that these different related objects are really the same, even though they are interrupted and variable. To justify this absurdity to ourselves, we often feign [= invent, pretend] some new and unintelligible thing that connects the objects together and prevents them from being interrupted and variable. The perceptions of our senses are intermittent {- there are gaps between them -} but we disguise this by feigning that they exist continuously; and they vary, but we disguise this by bringing in the notion of a soul or self or substance {which stays the same under all the variation}. Even in contexts where we do not indulge in such fictions, we are so strongly inclined to confuse identity with relatedness that we are apt to imagine something unknown and mysterious connecting the parts, other than the relations between them; and this is what I think happens when we ascribe identity to plants. When even this does not take place, we still feel impelled to confuse these ideas with one another, though we cannot give a satisfactory account of what we are doing or find anything invariable and uninterrupted to justify our notion of identity.

Thus the controversy about identity is not a merely verbal dispute. For when we attribute identity in an improper sense to variable or interrupted objects, we are not just using words wrongly but are engaging in a fiction, a false thought, either of something invariable and uninterrupted or of something mysterious and inexplicable. To convince a fair-minded person that this is so, we need only show him through his own daily experience that when variable or interrupted objects are supposed to continue the same, they really consist only in a sequence of parts, connected together by resemblance, contiguity, or causation. Such a sequence obviously fits our notion of diversity, so it can only be by mistake that we attribute an identity to it; and this mistake must arise from the fact that when the imagination moves from one of the related parts to the next, this act of the mind resembles the act in which we contemplate one continued object. What I mainly have to prove, then, is that whenever we ascribe identity to something which we do not observe to be unchanging and uninterrupted, what we are really talking about is {not a single object, but rather} a sequence of related objects.

To get started on this, suppose we have in front of us a mass of matter whose parts are contiguous and connected; clearly we have to attribute a perfect identity to this mass so long as it continues uninterruptedly to contain the very same parts, even if those parts move around within it. Now suppose that some very small or inconspicuous part is added to the mass or removed from it. Strictly speaking, it is no longer the same mass of matter; but we - not being accustomed to think so accurately - do not hesitate to say that a mass of matter is still "the same" if it changes only in such a trivial way. Our thought moves from the object before the change to the object after it so smoothly and easily that we are hardly aware that there is any movement; and this tempts us to think that it is nothing but a continued survey of the same object.

One aspect of this phenomenon is well worth noticing. Although a turnover in any large part of a mass of matter destroys the identity of the whole, {that is, makes us unwilling to say that it continues to be the same thing,} what we count as large in this context depends not on the actual size of the part but rather on how big a proportion it is of the whole. We would count a planet as still "the same" if it acquired or lost a mountain, but the change of a few inches could destroy the identity of some bodies. The only way to explain this is by supposing that objects interrupt the continuity of the mind's actions not according to their real size but according to their proportion to each other; and therefore, since this interruption makes an object cease to appear "the same", it must be the uninterrupted movement of the thought which constitutes the imperfect identity{, that is, which leads us to say that something is "the same" when, strictly speaking, it is not the same}.

This is confirmed by another phenomenon. Although a change in any considerable part of a body destroys its identity, if the change is produced gradually and imperceptibly we are less apt to see it as destroying the identity. The reason for this must be that the mind, in following the successive changes of the body, slides easily along from surveying its condition at one moment to surveying it at another, and is never aware of any interruption in its actions.

However careful we are to introduce changes gradually and to make each a small proportion of the whole, when eventually they add up to a considerable change we hesitate to attribute identity to such different objects. But we have a device through which we can induce the imagination to go one step further {in attributing identity where really there is none} - namely, relating the parts to one another through some common end or purpose. A ship of which a considerable part has been changed by frequent repairs is still considered "the same", even if the materials of which it is composed have come to be quite different. Through all the variations of the parts, they still serve the same common purpose; and that makes it easy for the imagination to move from one situation of the ship to another.

This happens even more strikingly when we see the parts as being causally related to one another in everything they do, in ways that reflect their common end. This {is not the case with ships, but it} is the case with all animals and vegetables: not only are the parts taken to have some over-all purpose, but also they depend on and are connected with one another {in ways that further that purpose}. The effect of this relation is that, although in a very few years both plants and animals go through a total change, with their form, size and substance being entirely altered, yet we still attribute identity to them. An oak that grows from a small plant to a large tree is still the same oak, {we say,} though there is not one particle of matter or shape of its parts that is the same. An infant becomes a man, and is sometimes fat, sometimes thin, without any change in his identity.

We should also consider two further noteworthy facts. The first is that though we can usually distinguish quite exactly between numerical and specific identity, yet sometimes we mix them up and use one in place of the other in our thinking and reasoning. [Numerical identity is real identity, or being the very same thing. It is called "numerical" because it affects counting: if x is not numerically identical with y, the x and y are two. By "specific identity" Hume means similarity, qualitative likeness, being of the same species, sort, or kind.] Thus, a man who hears a noise that is frequently interrupted and renewed says it is still "the same noise", though clearly the sounds have only a specific identity, that is, a resemblance, and there is nothing numerically the same but the cause which produced them. Similarly, when an old brick church fell to ruin, we may say that the parish rebuilt "the same church" out of sandstone and in a modern architectural style. Here neither the form nor the materials are the same; the buildings have nothing in common except their relation to the inhabitants of the parish; and yet this alone is enough to make us call them "the same". It is relevant that in these cases {of the noises and the churches} the first object is in a manner annihilated before the second comes into existence. That protects us from being presented at any one time with the idea of difference and multiplicity; {that is, we are not in a position to pick out both noises (or both churches) at the same time, and have the thought "This is one and that is another";} and that increases our willingness to call them "the same".

Secondly, although in general we do not attribute identity across a sequence of related objects unless the change of parts is gradual and only partial, with objects that are by nature changeable and inconstant we will say they are "the same" even if the changes are quite sudden. For example, the nature of a river consists in the motion and change of parts, so that there is a total turnover of these in less than twenty-four hours, but this does not stop the river from being "the same" for centuries. What is natural and essential to a thing is expected, and what is expected makes less impression and appears less significant than what is unusual and extraordinary. A big change of an expected kind looks smaller to the imagination than the most trivial unexpected alteration; and by making less of a break in the continuity of the thought it has less influence in destroying the {supposition of} identity.

I now proceed to explain the nature of personal identity, which has become such a great issue in philosophy. The line of reasoning which has so successfully explained the identity of plants and animals, of ships and houses, and of all changeable complex things - natural and artificial - must be applied to personal identity too. The identity which we ascribe to the mind of man is fictitious; it is like the identity we ascribe to plants and animals. So it cannot have a different origin from the latter, but must come from a similar operation of the imagination on similar objects.

That argument strikes me as perfectly conclusive, but if the reader is not convinced by it he should consider the following even tighter and more direct argument. It is obvious that the identity we attribute to the human mind, however perfect we may imagine it to be, cannot make many different perceptions become one by making them lose the distinctness and difference which are essential to them. Every distinct perception which enters into the mind's make-up is a distinct existence, and is different and distinguishable and separable from every other perception (whether occurring at the same time or at other times). Yet we suppose the whole sequence of perceptions to be united by identity {- we say that the members of the sequence are all perceptions of a single person -} which naturally raises a question about this relation of identity. Is it something that really binds together our various perceptions themselves, or does it only associate the ideas of them in the imagination? In other words, when we speak about the identity of a person, do we observe some real bond among his perceptions, or do we merely feel a bond among the ideas we form of those perceptions? The question is easy to answer, if we remember what has already been proved, namely that the understanding never observes any real connexion among objects, and that even the cause-effect relation, when strictly examined, comes down to a customary association of ideas. For that clearly implies that identity does not really belong to these different perceptions, holding them together, but is merely a quality which we attribute to them because of how the ideas of them are united in the imagination when we think about them. Now, the only qualities which can unite ideas in the imagination are the three I have mentioned. They are the uniting principles in the world of ideas; without them every distinct object is separable by the mind and can be separately thought about, and seems to be disconnected from every other object, not only from ones that are very dissimilar or distant. So identity must depend on some of the three relations of resemblance, contiguity, and causation. Now, the very essence of these relations consists in their making ideas follow one another easily; so our notions of personal identity must proceed entirely from the smooth and uninterrupted movement of thought along a sequence of connected ideas, in the way I have explained.

The only remaining question is: Which of the three relations produce this uninterrupted movement of our thought when we consider the successively existing perceptions which we take to constitute a mind or thinking person? Obviously contiguity has little or nothing to do with it; so we must attend to resemblance and causation.

Let us take resemblance first. If someone always remembers a large proportion of his past perceptions, this will contribute greatly to the holding of a certain relation within the sequence of his perceptions, varied as they may be. For memory is just a faculty by which we raise up images of past perceptions; and an image of something must resemble it. So {each memory involves a perception which resembles some past perception the person has had; and} the frequent occurrence of these resembling {pairs of} perceptions in the chain of thought makes it easier for the imagination to move from one link of the chain to another, making the whole sequence seem like the continuation of a single object. In this way, therefore, memory does not merely show the identity but also helps to create it, by bringing it about that many of the perceptions resemble one another. The account given in this paragraph applies equally to one's sense of one's own identity and to one's thoughts about the identity of others.

Causation also has a role. The true idea of the human mind is the idea of a system of different perceptions which are linked together by the cause-effect relation, through which they mutually produce, destroy, influence, and modify each other. Our impressions give rise to corresponding ideas, which in their turn produce other impressions. One thought chases another and draws after it a third by which it is expelled in its turn. In this respect the soul is very like a republic or commonwealth, in which the members are united by the links that connect rulers with subjects; these members cause others to come into existence {by begetting or giving birth to them}, and these in their turn keep the same republic continuously in existence throughout all the unceasing changes of its parts. And just as the same individual republic may change not only its members but also its laws and constitutions, so also the same person can vary his character and disposition as well as his impressions and ideas. Whatever changes he endures, his several parts are still connected by causation. Our emotions contribute to our identity just as our impressions and ideas do, by making some of our perceptions influence others that occur at very different times. This is what happens when we have a present concern for our past or future pains or pleasures.

Memory should be regarded as the source of personal identity, mainly because without it we would not know of the existence of this lengthy and continuous sequence of perceptions. If we had no memory, we would never have any notion of causation or, consequently, of that chain of causes and effects which constitute our self or person. Once we have acquired this notion of causation from our memory, we can extend the same chain of causes - and consequently the identity of our persons - beyond our memory, stretching it out to include times, circumstances and actions which we have entirely forgotten but which we suppose on general grounds to have existed. How many of our past actions do we actually remember? Who can tell me, for instance, what he thought and did on the 1st of January 1715, the 11th of March 1719 and the 3rd of August 1733? Or will he overturn all the most established notions of personal identity by saying that because he has forgotten the incidents of those days his present self is not the same person as the self of that time? Looked at from this angle, memory can be seen not to much to create personal identity as to discover it, by showing us the relation of cause and effect among our different perceptions. Those who contend that memory alone produces our personal identity ought to explain how we can in this way extend our identity beyond our memory.

The whole of this doctrine leads us to the very important conclusion that all the precise, subtle questions about personal identity can never be settled, and should be seen as verbal difficulties rather than philosophical ones. Identity depends on the relations of ideas; and these relations produce identity by means of that easy movement of thought that they give rise to. But the relations in question are matters of degree, and so is the easiness of the mental movement which depends on them; so we have no correct standard by which to settle when they acquire or lose their entitlement to the name "identity". {Just because the basis of our identity judgments consists in matters of degree, there can be borderline cases - just as there are borderlines for baldness, tallness and so on.} All the disputes about the identity of connected objects are merely verbal, except in so far as the relation of parts gives rise to some fiction - some imaginary principle of union - such as I have described.

What I have said about the origin and the uncertainty of our notion of the identity of the human mind can also be applied - with little or no change - to our notion of simplicity{, that is, the notion of a thing's not having parts}. An object whose different coexistent parts are closely related strikes the mind in much the same way as one that is perfectly simple and indivisible, and the thought of it does not require a much greater mental stretch. Because contemplating it is like contemplating something simple, we regard as though it were simple, and we invent a principle of union as the support of this simplicity and as the centre of all the different parts and qualities of the object.

I had hoped that however deficient my theory of the intellectual world might be, it would at least be free from those contradictions and absurdities which seem to infect every explanation that human reason can give of the material world. But reconsidering more carefully the section on personal identity I find myself involved in such a labyrinth that I do not know how to correct my former opinions, nor do I know how to make them consistent. If this is not a good general reason for scepticism, it is at least a sufficient one (as if I did not already have plenty) for me to be cautious and modest in all my conclusions. I shall present the arguments on both sides, starting with those that led me to deny the strict and proper identity and simplicity of a self or thinking being. {I offer seven of these, each pretty much independent of the others.}

(1) When we talk of self or substance we must associate ideas with these terms, otherwise they would be meaningless. Every idea is derived from previous impressions; and we have no impression of self or substance as something simple and individual. We have, therefore, no idea of them in that sense.

(2) Whatever is distinct is distinguishable, and whatever is distinguishable is separable by the thought or imagination. All perceptions are distinct. They are, therefore, distinguishable, and separable, and may be thought of as separately existent, and may exist separately, without any contradiction or absurdity.

When I view this table and that chimney, nothing is present to me but particular perceptions which are of the same kind as all other perceptions. This is the doctrine of philosophers. But this table and that chimney may and do exist separately. This is the doctrine of the common man, and it implies no contradiction. So there is no contradiction in extending the same doctrine to all perceptions {- that is, the doctrine that they can exist separately. The next paragraph gives an argument for this}.

The following reasoning seems satisfactory on the whole. All ideas are borrowed from previous perceptions. So our ideas of objects are derived from that source. Therefore any proposition which is intelligible and consistent with regard to objects must be equally so when applied to perceptions. But it is intelligible and consistent to say that objects exist independently, without having to inhere in any common simple substance. So it cannot be absurd to say the same thing about perceptions. {We are therefore not entitled to insist that there must be some self or substance in which our perceptions exists.}

(3) When I look in on myself, I can never perceive this self without

some one or more perceptions; nor can I ever perceive anything but the perceptions. It is a complex of these perceptions, therefore, which constitutes the self.

(4) We can conceive a thinking being to have as few perceptions as we like - even to be reduced to the level (below that of an oyster) of having only one perception, such as that of thirst or hunger. In considering such a mind, do you conceive anything more than merely that one perception? Have you any notion of self or substance? If not, the addition of other perceptions can never give you that notion.

(5) The annihilation which some people suppose to follow upon death, and which entirely destroys this self, is nothing but an extinction of all particular perceptions - love and hatred, pain and pleasure, thought and sensation. So these must be the same as the self, since the one cannot survive the other.

(6) Is self the same as substance? If it is, then there can be no question of the same self remaining when there is a change of substance. If on the other hand self and substance are distinct, what is the difference between them? For my part, I have no notion of either when they are conceived as distinct from particular perceptions.

(7) Philosophers are beginning to be reconciled to the principle that we have no idea of external substance distinct from the ideas of particular qualities. This should pave the way for a similar principle regarding the mind, namely that we have no notion of it distinct from the particular perceptions.

All of this seems clear and true. But having started my account with our particular perceptions all loose and separate, when I proceed to explain the principle of connexion which binds them together, making us attribute to them a real simplicity and identity, I come to realize that my account is very defective, and that I would not have accepted it if it weren't for the seeming power of the foregoing arguments. [Hume now re-states his own theory of personal identity, in a manner that is favourable to it. His subsequent worries and doubts start to surface only at the end of this paragraph.] If perceptions are distinct existences, they form a whole only by being connected together. But the human understanding can never discover connexions among distinct existences; we only feel a connexion in our mind when our thought is compelled to pass from one object to another. It follows, then, that personal identity is merely felt by our thought: this happens when our thought reflects on the sequence of past perceptions that compose a mind, and feels its the ideas of them to be inter-connected and to follow on from one another in a natural way. Extraordinary though it is, this conclusion need not surprise us. Most philosophers today seem inclined to think that personal identity arises from consciousness, and consciousness is nothing but a thought or perception directed inwards towards oneself. To that extent, this present philosophy of mine looks promising. [Now comes the trouble.] But all my hopes vanish when I come to explain the principles that unite our successive perceptions in our thought or consciousness. I cannot discover any satisfactory theory about this.

In short, there are two principles which I cannot render consistent, nor can I give either of them up: (i) all our distinct perceptions are distinct existences, and (ii) the mind never perceives any real connexion among distinct existences. If our perceptions either inhered in something simple and individual, or if the mind perceived some real connexion among them, there would be no difficulty. For my part, I must plead the privilege of a sceptic and confess that this problem is too hard for my understanding. I do not say outright that it is absolutely insoluble. Perhaps someone else - or even myself after further reflection - will discover some hypothesis that will reconcile those contradictions.