Philosophical Studies · G. E. Moore
HUME'S PHILOSOPHY
In both of his two books on the Human Understanding, Hume had, I think, one main general object. He tells us that it was his object to discover "the extent and force of human understanding," to give us "an exact analysis of its powers and capacity." And we may, I think, express what he meant by this in the following way. He plainly held (as we all do) that some men sometimes entertain opinions which they cannot know to be true. And he wished to point out what characteristics are possessed by those of our opinions which we _can_ know to be true, with a view of persuading us that any opinion which does _not_ possess any of these characteristics is of a kind which we _cannot_ know to be so. He thus tries to lay down certain rules to the effect that the _only_ propositions which we can, any of us, know to be true are of certain definite kinds. It is in this sense, I think, that he tries to define the limits of human understanding.
With this object he, first of all, divides all the propositions, which we can even so much as conceive, into two classes. They are all, he says, either propositions about "relations of ideas" or else about "matters of fact." By propositions about "relations of ideas" he means such propositions as that twice two are four, or that black differs from white; and it is, I think, easy enough to see, though by no means easy to define, what kind of propositions it is that he means to include in this division. They are, he says, the only kind of propositions with regard to which we can have "intuitive" or "demonstrative" certainty. But the vast majority of the propositions in which we believe and which interest us most, belong to the other division: they are propositions about "matters of fact." And these again he divides into two classes. So far as his words go, this latter division is between "matters of fact, beyond the present testimony of our senses, or the records of our memory," on the one hand, and matters of fact for which we _have_ the evidence of our memory or senses, on the other. But it is, I think, quite plain that these words do not represent quite accurately the division which he really means to make. He plainly intends to reckon along with facts for which we have the evidence of our _senses_ all facts for which we have the evidence of _direct observation_--such facts, for instance, as those which I observe when I observe that I am angry or afraid, and which cannot be strictly said to be apprehended by my _senses._ The division, then, which he really intends to make is (to put it quite strictly) into the two classes--(1) propositions which assert some matter of fact which I am (in the strictest sense) _observing_ at the moment, or which I have so observed in the past and now remember; and (2) propositions which assert any matter of fact which I am not now observing and never have observed, or, if I have, have quite forgotten.
We have, then, the three classes--(1) propositions which assert "relations of ideas"; (2) propositions which assert "matters of fact" for which we have the evidence of direct observation or personal memory; (3) propositions which assert "matters of fact_"_ for which we have _not_ this evidence. And as regards propositions of the first two classes, Hume does not seem to doubt our capacity for knowledge. He does not doubt that we can know _some_ (though, of course, not _all)_ propositions about "relations of ideas" to be true; he never doubts, for instance, that we can know that twice two are four. And he generally assumes also that each of us can know the truth of _all_ propositions which merely assert some matter of fact which we ourselves are, in the strictest sense, directly observing, or which we have so observed and now remember. He does, indeed, in one place, suggest a doubt whether our memory is _ever_ to be implicitly trusted, but he generally assumes that it _always_ can. It is with regard to propositions of the third class that he is chiefly anxious to determine which of them (if any) we can know to be true and which not. In what cases can any man know any matter of fact which he himself has not directly observed? It is Hume's views on this question which form, I think, the main interest of his philosophy.
He proposes, first of all, by way of answer to it, a rule, which may, I think, be expressed as follows: No man, he says, can ever know any matter of fact, which he has not himself observed, unless he can know that it is connected by "the relation of cause and effect," with some fact which he _has_ observed. And no man can ever know that any two facts are connected by this relation, except by the help of his own past _experience._ In other words, if I am to know any fact, A, which I have not myself observed, my past experience must give me some foundation for the belief that A is causally connected with some fact, B, which I have observed. And the only kind of past experience which can give me any foundation for such a belief is, Hume seems to say, as follows: I must, he says, have found _facts like_ A "constantly conjoined" in the past with _facts like_ B. This is what he _says;_ but we must not, I think, press his words too strictly. I may, for instance, know that A is _probably_ a fact, even where the conjunction of facts like it with facts like B has not been quite constant.
Or instead of observing facts like A conjoined with facts like B, I may have observed a whole series of conjunctions--for instance, between A and C, C and D, D and E, and E and B; and such a series, however long, will do quite as well to establish a causal connection between A and B, as if I had directly observed conjunctions between A and B themselves. Such modifications as this, Hume would, I think, certainly allow. But, allowing for them, his principle is, I think, quite clear. I can, he holds, never know any fact whatever, which I have not myself observed, unless I have observed similar facts in the past and have observed that they were "conjoined" (directly or indirectly) with facts similar to some fact which I do now observe or remember. In this sense, he holds, _all_ our knowledge of facts, beyond the reach of our own observation, is founded on _experience._ This is Hume's primary principle. But what consequences does he think will follow from it, as to the kind of facts, beyond our own observation, which we can know? We may, I think, distinguish three entirely different views as to its consequences, which he suggests in different parts of his work.
In the first place, where he is specially engaged in explaining this primary principle, he certainly seems to suppose that all propositions of the kind, which we assume most universally in everyday life, may be founded on experience in the sense required. He supposes that we have this foundation in experience for such beliefs as that "a stone will fall, or fire burn"; that Julius Caesar was murdered; that the sun will rise to-morrow; that all men are mortal He speaks as if experience did not merely render such beliefs probable, but actually _proved_ them to be true. The "arguments from experience" in their favour are, he says, such as "leave no room for doubt or opposition." The only kinds of belief, which he definitely mentions as _not_ founded on experience, are "popular superstitions" on the one hand, and certain religious and philosophical beliefs, on the other. He seems to suppose that a few (a very few) religious beliefs may, perhaps, be founded on experience. But as regards most of the specific doctrines of Christianity, for example, he seems to be clear that they are not so founded. The belief in miracles is not founded on experience; nor is the philosophical belief that every event is caused by the direct volition of the Deity. In short, it would seem, that in this doctrine that our knowledge of unobserved facts is confined to such as are "founded on experience," he means to draw the line very much where it is drawn by the familiar doctrine which is called "Agnosticism." We can know such facts as are asserted in books on "history, geography or astronomy," or on "politics, physics and chemistry," because such assertions may be "founded on experience"; but we cannot know the greater part of the facts asserted in books "of divinity or school metaphysics," because such assertions have no foundation in experience.
This, I think, was clearly one of Hume's views. He meant to fix the limits of our knowledge at a point which would _exclude_ most religious propositions and a great many philosophical ones, as incapable of being known; but which would _include_ all the other kinds of propositions, which are most universally accepted by common-sense, as capable of being known. And he thought that, so far as matters of fact beyond the reach of our personal observation are concerned, this point coincided with that at which the possibility of "foundation on experience" ceases. But, if we turn to another part of his work, we find a very different view suggested. In a quite distinct section of both his books, he investigates the beliefs which we entertain concerning the existence of "external objects." And he distinguishes two different kinds of belief which may be held on this subject. "Almost all mankind, and philosophers themselves, for the greatest part of their lives," believe, he says, that "the very things they feel and see" _are_ external objects, in the sense that they continue to exist, even when we cease to feel or see them. Philosophers, on the other hand, have been led to reject this opinion and to suppose (when they reflect) that what we actually perceive by the senses never exists except when we perceive it, but that there are other external objects, which do exist independently of us, and which _cause_ us to perceive what we do perceive. Hume investigates both of these opinions, at great length in the _Treatise_, and much more briefly in the _Enquiry_, and comes to the conclusion, in both books, that neither of them can be "founded on experience," in the sense he has defined. As regards the first of them, the vulgar opinion, he does seem to admit in the _Treatise_ that it is, in a sense, founded on experience; but not, he insists, in the sense defined. And he seems also to think that, apart from this fact, there are conclusive reasons for holding that the opinion cannot be true. And as regards the philosophical opinion, he says that any belief in external objects, which we never perceive but which cause our perceptions, cannot possibly be founded on experience, for the simple reason that if it were, we should need to have directly observed some of these objects and their "conjunction" with what we do perceive, which _ex hypothesi,_ we cannot have done, since we never do directly observe any external object.
Hume, therefore, concludes, in this part of his work, that we cannot know of the existence of any "external object" whatever. And though in all that he says upon this subject, he is plainly thinking only of _material_ objects, the principles by which he tries to prove that we cannot know these must, I think, prove equally well that we cannot know any "external object" whatever--not even the existence of any other human mind. His argument is: We cannot directly observe any object whatever, except such as exist only when we observe them; we cannot, therefore, observe any "constant conjunctions" except between objects of this kind: and hence we can have no foundation in experience for any proposition which asserts the existence of any other kind of object, and cannot, therefore, know any such proposition to be true. And this argument must plainly apply to all the feelings, thoughts and perceptions of other men just as much as to material objects.
I can never know that any perception of mine, or anything which I do observe, must have been caused by any other man, because I can never directly observe a "constant conjunction" between any other man's thoughts or feelings or intentions and anything which I directly observe: I cannot, therefore, know that any other man ever had any thoughts or feelings--or, in short, that any man beside myself ever existed. The view, therefore, which Hume suggests in this part of his work, flatly contradicts the view which he at first seemed to hold. He now says we _cannot_ know that a stone will fall, that fire will burn, or the sun will rise to-morrow. All that I can possibly know, according to his present principles, is that _I shall see_ a stone fall, shall feel the fire burn, shall see the sun rise to-morrow. I cannot even know that any other men will see these things; for I cannot know that any other men exist. For the same reason, I cannot know that Julius Caesar was murdered, or that all men are mortal. For these are propositions asserting "external" facts--facts which don't exist only at the moment when I observe them; and, according to his present doctrine, I cannot possibly know any such proposition to be true. No man, in short, can know any proposition about "matters of fact" to be true, except such as merely assert something about _his own_ states of mind, past, present or future--about these or about what _he himself_ has directly observed, is observing, or will observe.
Here, therefore, we have a very different view suggested, as to the limits of human knowledge. And even this is not all. There is yet a third view, inconsistent with both of these, which Hume suggests in some parts of his work. So far as we have yet seen, he has not in any way contradicted his original supposition that we can know _some_ matters of fact, which we have never ourselves observed. In the second theory, which I have just stated, he does not call in question the view that I can know all such matters of fact as I know to be causally connected with facts which I have observed, nor the view that I can know some facts to be thus causally connected. All that he has done is to question whether I can know any _external_ fact to be causally connected with anything which I observe; he would still allow that I may be able to know that future states of my own, or past states, which I have forgotten, are causally connected with those which I now observe or remember; and that I may know therefore, in some cases, what I shall experience in the future, or have experienced in the past but have now forgotten. But in some parts of his work he does seem to question whether any man can know even as much as this: he seems to question whether we can ever know any fact whatever to be causally connected with any other fact.
For, after laying it down, as we saw above, that we cannot know any fact, A, to be causally connected with another, B, unless we have experienced in the past a constant conjunction between facts like A and facts like B, he goes on to ask what foundation we have for the conclusion that A and B _are_ causally connected, even when we _have_ in the past experienced a constant conjunction between them. He points out that from the fact that A has been constantly conjoined with B in the past, it does not follow that it ever will be so again. It does not follow, therefore, that the two really are causally connected in the sense that, when the one occurs, the other _always_ will occur also. And he concludes, for this and other reasons, that _no argument_ can assure us that, because they have been constantly conjoined in the past, therefore they really are causally connected. What, then, he asks, is the foundation for such an inference? _Custom,_ he concludes, is the only foundation. It is nothing but custom which induces us to believe that, because two facts have been constantly conjoined on many occasions, therefore they will be so on _all_ occasions.
We have, therefore, no better foundation than custom for any conclusion whatever as to facts which we have not observed. And can we be said really to _know_ any fact, for which we have no better foundation than this? Hume himself, it must be observed, never says that we can't. But he has been constantly interpreted as if the conclusion that we can't really know any one fact to be causally connected with any other, did follow from this doctrine of his. And there is, I think, certainly much excuse for this interpretation in the tone in which he speaks. He does seem to suggest that a belief which is _merely_ founded on custom, can scarcely be one which we _know_ to be true. And, indeed, he owns himself that, when he considers that this is our only foundation for any such belief, he is sometimes tempted to doubt whether we do know any fact whatever, except those which we directly observe. He does, therefore, at least suggest the view that every man's knowledge is entirely confined to those facts, which he is directly observing at the moment, or which he has observed in the past, and now remembers.
We see, then, that Hume suggests, at least, three entirely different views as to the consequences of his original doctrine. His original doctrine was that, as regards matters of fact beyond the reach of our own actual observation, the knowledge of each of us is strictly limited to those for which we have a basis in our own experience. And his first view as to the consequences of this doctrine was that it does show us to be incapable of knowing a good many religious and philosophical propositions, which many men have claimed that they knew; but that it by no means denies our capacity of knowing the vast majority of facts beyond our own observation, which we all commonly suppose that we know. His second view, on the other hand, is that it cuts off at once all possibility of our knowing the vast majority of these facts; since he implies that we cannot have any basis in experience for asserting any _external_ fact whatever--any fact, that is, except facts relating to our own actual past and future observations. And his third view is more sceptical still, since it suggests that we cannot really know any fact whatever, beyond the reach of our present observation or memory, even where we _have_ a basis in experience for such a fact: it suggests that experience cannot ever let us _know_ that any two things are causally connected, and therefore that it cannot give us _knowledge_ of any fact based on this relation.
What are we to think of these three views, and of the original doctrine from which Hume seems to infer them? As regards the last two views, it may perhaps be thought that they are too absurd to deserve any serious consideration. It is, in fact, absurd to suggest that I do not know any external facts whatever; that I do not know, for instance, even that there are any men beside myself. And Hume himself, it might seem, does not seriously expect or wish us to accept these views. He points out, with regard to all such excessively sceptical opinions that we cannot continue to believe them for long together--that, at least, we cannot, for long together, avoid believing things flatly inconsistent with them. The philosopher may believe, when he is philosophising, that no man knows of the existence of any other man or of any material object; but at other times he will inevitably believe, as we all do, that he does know of the existence of this man and of that, and even of this and that material object. There can, therefore, be no question of making all our beliefs consistent with such views as this of never believing anything that is inconsistent with them. And it may, therefore, seem useless to discuss them.
But in fact, it by no means follows that, because we are not able to adhere consistently to a given view, therefore that view is false; nor does it follow that we may not sincerely believe it, whenever we are philosophising, even though the moment we cease to philosophise, or even before, we may be forced to contradict it. And philosophers do, in fact, sincerely believe such things as this--things which flatly contradict the vast majority of the things which they believe at other times. Even Hume, I think, does sincerely wish to persuade us that we cannot know of the existence of external material objects--that this is a philosophic truth, which we ought, if we can, so long as we are philosophising, to believe. Many people, I think, are certainly tempted, in their philosophic moments, to believe such things; and, since this is so, it is, I think, worth while to consider seriously what arguments can be brought against such views. It is worth while to consider whether they are views which we ought to hold as philosophical opinions, even if it be quite certain that we shall never be able to make the views which we entertain at other times consistent with them. And it is the more worth while, because the question how we can prove or disprove such extreme views as these, has a bearing on the question how we can, in any case whatever, prove or disprove that we do really _know,_ what we suppose ourselves to know.
What arguments, then, are there for or against the extreme view that no man can know any external fact whatever; and the still more extreme view that no man can know any matter of fact whatever, except those which he is directly observing at the moment, or has observed in the past and now remembers? It may be pointed out, in the first place, that, if these views are true, then at least no man can possibly know them to be so. What these views assert is that I cannot know any external fact whatever. It follows, therefore, that I cannot know that there are any other men, beside myself, and that they are like me in this respect. Any philosopher who asserts positively that other men, equally with himself, are incapable of knowing any external facts, is, in that very assertion, contradicting himself, since he implies that he _does_ know a great many facts about the knowledge of other men. No one, therefore, can be entitled to assert positively that human knowledge is limited in this way, since, in asserting it positively, he is implying that his own knowledge is not so limited. It cannot be proper, even in our philosophic moments, to take up such an attitude as this.
No one, therefore, can know positively that men in general, are incapable of knowing external facts. But still, although we cannot _know_ it, it remains possible that the view should be a true one. Nay, more, it remains possible that a man should know that _he himself_ is incapable of knowing any external facts, and that, _if_ there are any other men whose faculties are only similar to his own, they also must be incapable of knowing any. The argument just used obviously does not apply against such a position as this. It only applies against the position that men in general positively are incapable of knowing external facts: it does not apply against the position that the philosopher himself is incapable of knowing any, or against the position that there are _possibly_ other men in the same case, and that, if their faculties are similar to the philosopher's, they certainly would be in it. I do not contradict myself by maintaining positively that _I_ know no external facts, though I do contradict myself if I maintain that I am only one among other men, and that no man knows any external facts. So far, then, as Hume merely maintains that _he_ is incapable of knowing any external facts, and that there _may_ be other men like him in this respect, the argument just used is not valid against his position. Can any conclusive arguments be found against it?
Ideas discussed in this chapter
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