Philosophy

by Bertrand Russell

[15] See Holt’s Concept of Consciousness, preface.

Since man is the instrument of his own knowledge, it is necessary to study him as an instrument before we can appraise the value of what our senses seem to tell us concerning the world. In [Part I] we studied man, within the framework of common-sense beliefs, just as we might study clocks or thermometers, as an instrument sensitive to certain features of the environment, since sensitiveness to the environment is obviously an indispensable condition for knowledge about it.

In [Part II] we advanced to the study of the physical world. We found that matter, in modern science, has lost its solidity and substantiality; it has become a mere ghost haunting the scenes of its former splendours. In pursuit of something that could be treated as substantial, physicists analysed ordinary matter into molecules, molecules into atoms, atoms into electrons and protons. There, for a few years, analysis found a resting-place. But now electrons and protons themselves are dissolved into systems of radiations by Heisenberg, and into systems of waves by Schrödinger—the two theories amount mathematically to much the same thing. And these are not wild metaphysical speculations; they are sober mathematical calculations, accepted by the great majority of experts.

Another department of theoretical physics, the theory of relativity, has philosophical consequences which are, if possible, even more important. The substitution of space-time for space and time has made the category of substance less applicable than formerly, since the essence of substance was persistence through time, and there is now no one cosmic time. The result of this is to turn the physical world into a four-dimensional continuum of events, instead of a series of three-dimensional states of a world composed of persistent bits of matter. A second important feature of relativity-theory is the abolition of force, particularly gravitational force, and the substitution of differential causal laws having to do only with the neighbourhood of an event, not with an influence exerted from a distance, such as gravitation formerly seemed to be.

The modern study of the atom has had two consequences which have considerably changed the philosophical hearing of physics. On the one hand, it appears that there are discontinuous changes in nature, occasions when there is a sudden jump from one state to another without passing through the intermediate states. (Schrödinger, it is true, questions the need for assuming discontinuity; but so far his opinion has not prevailed.) On the other hand, the course of nature is not so definitely determined by the physical laws at present known as it was formerly thought to be. We cannot predict when a discontinuous change will take place in a given atom, though we can predict statistical averages. It can no longer be said that, given the laws of physics and the relevant facts about the environment, the future history of an atom can theoretically be calculated from its present condition. It may be that this is merely due to the insufficiency of our knowledge, but we cannot be sure that this is the case. As things stand at present, the physical world is not so rigidly deterministic as it has been believed to be during the last 250 years. And in various directions what formerly appeared as laws governing each separate atom are now found to be only averages attributable in part to the laws of chance.

From these questions concerning the physical world in itself, we were led to others concerning the causation of our perceptions, which are the data upon which our scientific knowledge of physics is based. We saw that a long causal chain always intervenes between an external event and the event in us which we regard as perception of the external event. We cannot therefore suppose that the external event is exactly what we see or hear; it can, at best, resemble the percept only in certain structural respects. This fact has caused considerable confusion in philosophy, partly because philosophers tried to think better of perception than it deserves, partly because they failed to have clear ideas on the subject of space. It is customary to treat space as a characteristic of matter as opposed to mind, but this is only true of physical space. There is also perceptual space, which is that in which what we know immediately through the senses is situated. This space cannot be identified with that of physics. From the standpoint of physical space, all our percepts are in our heads; but in perceptual space our percept of our hand is outside our percept of our head. The failure to keep physical and perceptual space distinct has been a source of great confusion in philosophy.

In [Part III] we resumed the study of man, but now as he appears to himself, not only as he is known to an external observer. We decided, contrary to the view of the behaviourists, that there are important facts which cannot be known except when the observer and observed are the same person. The datum in perception, we decided, is a private fact which can only be known directly to the percipient; it is a datum for physics and psychology equally, and must be regarded as both physical and mental. We decided later that there are inductive grounds, giving probability but not certainty, in favour of the view that perceptions are causally connected with events which the percipient does not experience, which may belong only to the physical world.

The behaviour of human beings is distinguished from that of inanimate matter by what are called “mnemic” phenomena, i.e. by a certain kind of effect of past occurrences. This kind of effects is exemplified in memory, in learning, in the intelligent use of words, and in every kind of knowledge. But we cannot, on this ground, erect an absolute barrier between mind and matter. In the first place, inanimate matter, to some slight extent, shows analogous behaviour—e.g. if you unroll a roll of paper, it will roll itself up again. In the second place, we find that living bodies display mnemic phenomena to exactly the same extent to which minds display them. In the third place, if we are to avoid what I have called “mnemic” causation, which involves action at a distance in time, we must say that mnemic phenomena in mental events are due to the modification of the body by past events. That is to say, the set of events which constitutes one man’s experience is not causally self-sufficient, but is dependent upon causal laws involving events which he cannot experience.

On the other hand, our knowledge of the physical world is purely abstract: we know certain logical characteristics of its structure, but nothing of its intrinsic character. There is nothing in physics to prove that the intrinsic character of the physical world differs, in this or that respect, from that of the mental world. Thus from both ends, both by the analysis of physics and by the analysis of psychology, we find that mental and physical events form one causal whole, which is not known to consist of two different sorts. At present, we know the laws of the physical world better than those of the mental world, but that may change. We know the intrinsic character of the mental world to some extent, but we know absolutely nothing of the intrinsic character of the physical world. And in view of the nature of the inferences upon which our knowledge of physics rests, it seems scarcely possible that we should ever know more than abstract laws about matter.

In [Part IV] we considered what philosophy has to say about the universe. The function of philosophy, according to the view advocated in this volume, is somewhat different from that which has been assigned to it by a large and influential school. Take, e.g. Kant’s antinomies. He argues (1) that space must be infinite, (2) that space cannot be infinite; and he deduces that space is subjective. The non-Euclideans refuted the argument that it must be infinite, and Georg Cantor refuted the argument that it cannot be. Formerly, a priori logic was used to prove that various hypotheses which looked possible were impossible, leaving only one possibility, which philosophy therefore pronounced true. Now a priori logic is used to prove the exact contrary, namely, that hypotheses which looked impossible are possible. Whereas logic was formerly counsel for the prosecution, it is now counsel for the defence. The result is that many more hypotheses are at large than was formerly the case. Formerly, to revert to the instance of space, it appeared that experience left only one kind of space to logic, and logic showed this one kind to be impossible. Now, logic presents many kinds of space as possible apart from experience, and experience only partially decides between them. Thus, while our knowledge of what is has become less than it was formerly supposed to be, our knowledge of what may be is enormously increased. Instead of being shut in within narrow walls, of which every nook and cranny could be explored, we find ourselves in an open world of free possibilities, where much remains unknown because there is so much to know. The attempt to prescribe to the universe by means of a priori principles has broken down; logic, instead of being, as formerly, a bar to possibilities, has become the great liberator of the imagination, presenting innumerable alternatives which are closed to unreflective common sense, and leaving to experience the task of deciding, where decision is possible, between the many worlds which logic offers for our choice.