The fourth of the above theories, which admits events that no one perceives, may also be defended by invalid arguments. It may be held that causality is known a priori, and that causal laws are impossible unless there are unperceived events. As against this, it may be urged that causality is not a priori, and that whatever regularity can be observed must be in relation to percepts. Whatever there is reason to believe in the laws of physics must, it would seem, be capable of being stated in terms of percepts. The statement may be odd and complicated; it may lack the characteristic of continuity which, until lately, was expected of a physical law. But it can hardly be impossible.
I conclude that there is no a priori objection to any one of our four theories. It is possible, however, to say that all truth is pragmatic, and that there is no pragmatic difference between the four theories. If this is true, we can adopt whichever we please, and the difference between them is only linguistic. I cannot accept this view; but this, also, is a matter for discussion at a later stage.
It remains to be asked whether any meaning can be attached to the words “mind” and “matter.” Every one knows that “mind” is what an idealist thinks there is nothing else but, and “matter” is what a materialist thinks the same about. The reader knows also, I hope, that idealists are virtuous and materialists are wicked. But perhaps there may be more than this to be said.
My own definition of “matter” may seem unsatisfactory; I should define it as what satisfies the equations of physics. There may be nothing satisfying these equations; in that case either physics or the concept “matter” is a mistake. If we reject substance, “matter” will have to be a logical construction. Whether it can be any construction composed of events—which may be partly inferred—is a difficult question, but by no means an insoluble one.
As for “mind,” when substance has been rejected a mind must be some group or structure of events. The grouping must be effected by some relation which is characteristic of the sort of phenomena we wish to call “mental.” We may take memory as typical. We might—though this would be rather unduly simple—define a “mental” event as one which remembers or is remembered. Then the “mind” to which a given mental event belongs is the group of events connected with the given event by memory-chains, backwards or forwards.
It will be seen that, according to the above definitions, a mind and a piece of matter are, each of them, a group of events. There is no reason why every event should belong to a group of one kind or the other, and there is no reason why some events should not belong to both groups; therefore some events may be neither mental nor material, and other events may be both. As to this, only detailed empirical considerations can decide.
CHAPTER XVII
Hume
DAVID HUME (1711-76) is one of the most important among philosophers, because he developed to its logical conclusion the empirical philosophy of Locke and Berkeley, and by making it self-consistent made it incredible. He represents, in a certain sense, a dead end: in his direction, it is impossible to go further. To refute him has been, ever since he wrote, a favourite pastime among metaphysicians. For my part, I find none of their refutations convincing; nevertheless, I cannot but hope that something less sceptical than Hume’s system may be discoverable.
His chief philosophical work, the Treatise of Human Nature, was written while he was living in France during the years 1734 to 1737. The first two volumes were published in 1739, the third in 1740. He was a very young man, not yet in his thirties; he was not well known, and his conclusions were such as almost all schools would find unwelcome. He hoped for vehement attacks, which he would meet with brilliant retorts. Instead, no one noticed the book; as he says himself, “it fell dead-born from the press.” “But,” he adds, “being naturally of a cheerful and sanguine temper, I very soon recovered from the blow.” He devoted himself to the writing of essays, of which he produced the first volume in 1741. In 1744 he made an unsuccessful attempt to obtain a professorship at Edinburgh; having failed in this, he became first tutor to a lunatic and then secretary to a general. Fortified by these credentials, he ventured again into philosophy. He shortened the Treatise by leaving out the best parts and most of the reasons for his conclusions; the result was the Inquiry into Human Understanding, for a long time much better known than the Treatise. It was this book that awakened Kant from his “dogmatic slumbers”; he does not appear to have known the Treatise.
He wrote also Dialogues Concerning Natural Religion, which he kept unpublished during his lifetime. By his direction, they were published posthumously in 1779. His Essay on Miracles, which became famous, maintains that there can never be adequate historical evidence for such events.
His History of England, published in 1755 and following years, devoted itself to proving the superiority of Tories to Whigs and of Scotchmen to Englishmen; he did not consider history worthy of philosophic detachment. He visited Paris in 1763, and was made much of by the philosophes. Unfortunately, he formed a friendship with Rousseau, and had a famous quarrel with him. Hume behaved with admirable forbearance, but Rousseau, who suffered from persecution mania, insisted upon a violent breach.
Hume has described his own character in a self-obituary, or “funeral oration,” as he calls it: “I was a man of mild dispositions, of command of temper, of an open, social and cheerful humour, capable of attachment, but little susceptible of enmity, and of great moderation in all my passions. Even my love of literary fame, my ruling passion, never soured my temper, notwithstanding my frequent disappointments.” All this is borne out by everything that is known of him.
Hume’s Treatise of Human Nature is divided into three books, dealing respectively with the understanding, the passions, and morals. What is important and novel in his doctrines is in the first book, to which I shall confine myself.
He begins with the distinction between “impressions” and “ideas.” These are two kinds of perceptions, of which impressions are those that have more force and violence. “By ideas I mean the faint images of these in thinking and reasoning.” Ideas, at least when simple, are like impressions, but fainter. “Every simple idea has a simple impression, which resembles it; and every simple impression a correspondent idea.” “All our simple ideas in their first appearance are derived from simple impressions, which are correspondent to them, and which they exactly represent.” Complex ideas, on the other hand, need not resemble impressions. We can imagine a winged horse without having ever seen one, but the constituents of this complex idea are all derived from impressions. The proof that impressions come first is derived from experience; for example, a man born blind has no ideas of colours. Among ideas, those that retain a considerable degree of the vivacity of the original impressions belong to memory, the others to imagination.
There is a section (Book I, Part I, Sec. VII) “Of Abstract Ideas,” which opens with a paragraph of emphatic agreement with Berkeley’s doctrine that “all general ideas are nothing but particular ones, annexed to a certain term, which gives them a more extensive significance, and makes them recall upon occasion other individuals, which are similar to them.” He contends that, when we have an idea of a man, it has all the particularity that the impression of a man has. “The mind cannot form any notion of quantity or quality without forming a precise notion of degrees of each.” “Abstract ideas are in themselves individual, however they may become general in their representation.” This theory, which is a modern form of nominalism, has two defects, one logical, the other psychological. To begin with the logical objection: “When we have found a resemblance among several objects,” Hume says, “we apply the same name to all of them.” Every nominalist would agree. But in fact a common name, such as “cat,” is just as unreal as the universal CAT is. The nominalist solution of the problem of universals thus fails through being insufficiently drastic in the application of its own principles; it mistakenly applies these principles only to “things,” and not also to words.
The psychological objection is more seriou
s, at least in connection with Hume. The whole theory of ideas as copies of impressions, as he sets it forth, suffers from ignoring vagueness. When, for example, I have seen a flower of a certain colour, and I afterwards call up an image of it, the image is lacking in precision, in this sense, that there are several closely similar shades of colour of which it might be an image, or “idea,” in Hume’s terminology. It is not true that “the mind cannot form any notion of quantity or quality without forming a precise notion of degrees of each.” Suppose you have seen a man whose height is six feet one inch. You retain an image of him, but it probably would fit a man half an inch taller or shorter. Vagueness is different from generality, but has some of the same characteristics. By not noticing it, Hume runs into unnecessary difficulties, for instance, as to the possibility of imagining a shade of colour you have never seen, which is intermediate between two closely similar shades that you have seen. If these two are sufficiently similar, any image you can form will be equally applicable to both of them and to the intermediate shade. When Hume says that ideas are derived from impressions which they exactly represent he goes beyond what is psychologically true.
Hume banished the conception of substance from psychology, as Berkeley had banished it from physics. There is, he says, no impression of self, and therefore no idea of self (Book I, Part IV, Sec. VI). “For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never catch myself at any time without a perception, and never can observe anything but the perception.” There may, he ironically concedes, be some philosophers who can perceive their selves; “but setting aside some metaphysicians of this kind, I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with inconceivable rapidity, and are in a perpetual flux and movement.”
This repudiation of the idea of the Self is of great importance. Let us see exactly what it maintains, and how far it is valid. To begin with, the Self, if there is such a thing, is never perceived, and therefore we can have no idea of it. If this argument is to be accepted, it must be carefully stated. No man perceives his own brain, yet, in an important sense, he has an “idea” of it. Such “ideas,” which are inferences from perceptions, are not among the logically basic stock of ideas; they are complex and descriptive—this must be the case if Hume is right in his principle that all simple ideas are derived from impressions, and if this principle is rejected, we are forced back on “innate” ideas. Using modern terminology, we may say: Ideas of unperceived things or occurrences can always be defined in terms of perceived things or occurrences, and therefore, by substituting the definition for the term defined, we can always state what we know empirically without introducing any unperceived things or occurrences. As regards our present problem, all psychological knowledge can be stated without introducing the “Self.” Further, the “Self,” as defined, can be nothing but a bundle of perceptions, not a new simple “thing.” In this I think that any thoroughgoing empiricist must agree with Hume.
It does not follow that there is no simple Self; it only follows that we cannot know whether there is or not, and that the Self, except as a bundle of perceptions, cannot enter into any part of our knowledge. This conclusion is important in metaphysics, as getting rid of the last surviving use of “substance.” It is important in theology, as abolishing all supposed knowledge of the “soul.” It is important in the analysis of knowledge, since it shows that the category of subject and object is not fundamental. In this matter of the ego Hume made an important advance on Berkeley.
The most important part of the whole Treatise is the section called “Of Knowledge and Probability.” Hume does not mean by “probability” the sort of knowledge contained in the mathematical theory of probability, such as that the chance of throwing double sixes with two dice is one thirty-sixth. This knowledge is not itself probable in any special sense; it has as much certainty as knowledge can have. What Hume is concerned with is uncertain knowledge, such as is obtained from empirical data by inferences that are not demonstrative. This includes all our knowledge as to the future, and as to unobserved portions of the past and present. In fact, it includes everything except, on the one hand, direct observation, and, on the other, logic and mathematics. The analysis of such “probable” knowledge led Hume to certain sceptical conclusions, which are equally difficult to refute and to accept. The result was a challenge to philosophers, which, in my opinion, has still not been adequately met.
Hume begins by distinguishing seven kinds of philosophical relation: resemblance, identity, relations of time and place, proportion in quantity or number, degrees in any quality, contrariety, and causation. These, he says, may be divided into two kinds: those that depend only on the ideas, and those that can be changed without any change in the ideas. Of the first kind are resemblance, contrariety, degrees in quality, and proportions in quantity or number. But spatio-temporal and causal relations are of the second kind. Only relations of the first kind give certain knowledge; our knowledge concerning the others is only probable. Algebra and arithmetic are the only sciences in which we can carry on a long chain of reasoning without losing certainty. Geometry is not so certain as algebra and arithmetic, because we cannot be sure of the truth of its axioms. It is a mistake to suppose, as many philosophers do, that the ideas of mathematics “must be comprehended by a pure and intellectual view, of which the superior faculties of the soul are alone capable.” The falsehood of this view is evident, says Hume, as soon as we remember that “all our ideas are copied from our impressions.”
The three relations that depend not only on ideas are identity, spatio-temporal relations, and causation. In the first two, the mind does not go beyond what is immediately present to the senses. (Spatio-temporal relations, Hume holds, can be perceived, and can form parts of impressions.) Causation alone enables us to infer some thing or occurrence from some other thing or occurrence: “’Tis only causation, which produces such a connexion, as to give us assurance from the existence or action of one object, that ’twas followed or preceded by any other existence or action.”
A difficulty arises from Hume’s contention that there is no such thing as an impression of a causal relation. We can perceive, by mere observation of A and B. that A is above B, or to the right of B, but not that A causes B. In the past, the relation of causation had been more or less assimilated to that of ground and consequent in logic, but this, Hume rightly perceived, was a mistake.
In the Cartesian philosophy, as in that of the Scholastics, the connection of cause and effect was supposed to be necessary, as logical connections are necessary. The first really serious challenge to this view came from Hume, with whom the modern philosophy of causation begins. He, in common with almost all philosophers down to and including Bergson, supposes the law to state that there are propositions of the form “A causes B,” where A and B are classes of events; the fact that such laws do not occur in any well-developed science appears to be unknown to philosophers. But much of what they have said can be translated so as to be applicable to causal laws such as do occur; we may, therefore, ignore this point for the present.
Hume begins by observing that the power by which one object produces another is not discoverable from the ideas of the two objects, and that we can therefore only know cause and effect from experience, not from reasoning or reflection. The statement “what begins must have a cause,” he says, is not one that has intuitive certainty, like the statements of logic. As he puts it: “There is no object, which implies the existence of any other if we consider these objects in themselves, and never look beyond the ideas which we form of them.” Hume argues from this that it must be experience that gives knowledge of cause and effect, but that it cannot be merely the experience of the two events A and B which are in a causal relation to each other. It must be experience, because the connection is not logical; an
d it cannot be merely the experience of the particular events A and B, since we can discover nothing in A by itself which should lead it to produce B. The experience required, he says, is that of the constant conjunction of events of the kind A with events of the kind B. He points out that when, in experience, two objects are constantly conjoined, we do in fact infer one from the other. (When he says “infer,” he means that perceiving the one makes us expect the other; he does not mean a formal or explicit inference.) “Perhaps, the necessary connection depends on the inference,” not vice versa. That is to say, the sight of A causes the expectation of B, and so leads us to believe that there is a necessary connection between A and B. The inference is not determined by reason, since that would require us to assume the uniformity of nature, which itself is not necessary, but only inferred from experience.
Hume is thus led to the view that, when we say “A causes B,” we mean only that A and B are constantly conjoined in fact, not that there is some necessary connection between them. “We have no other notion of cause and effect, but that of certain objects, which have been always conjoined together…. We cannot penetrate into the reason of the conjunction.”
He backs up his theory with a definition of “belief,” which is, he maintains, “a lively idea related to or associated with a present impression.” Through association, if A and B have been constantly conjoined in past experience, the impression of A produces that lively idea of B which constitutes belief in B. This explains why we believe A and B to be connected: the percept of A is connected with the idea of B, and so we come to think that A is connected with B, though this opinion is really groundless. “Objects have no discoverable connexion together; nor is it from any other principle but custom operating upon the imagination, that we can draw any inference from the appearance of one to the experience of another.” He repeats many times the contention that what appears to us as necessary connection among objects is really only connection among the ideas of those objects: the mind is determined by custom, and “’tis this impression, or determination, which affords me the idea of necessity.” The repetition of instances, which leads us to the belief that A causes B, gives nothing new in the object, but in the mind leads to an association of ideas; thus “necessity is something that exists in the mind, not in objects.”
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