History of Western Philosophy - Bertrand Russell [377]
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 that 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