Bertrand Russell

“ There is of course another quality which we wish our knowledge to possess, namely, comprehensiveness: we wish the area of our knowledge to be as wide as possible. But this is the business of science rather than of philosophy. A man does not necessarily become a better philosopher through knowing more scientific facts; it is principles and methods and general conceptions that he should learn from science if philosophy is what interests him. The philosopher’s work is, so to speak, at the second remove from crude fact. Science tries to collect facts into bundles by means of scientific laws ”

“ We naturally think of an atom as being like a billiard-ball; we should do better to think of it as like a ghost, which has no "pushiness" and yet can make you fly. We have to change our notions both of substance and of cause. To say that an atom persists is like saying that a tune persists. If a tune takes five minutes to play, we do not conceive of it as a single thing which exists throughout that time, but as a series of notes, so related as to form a unity. In the case of the tune, the unity is æsthetic; in the case of the atom, it is causal. ”

“ Let us take first the belief in common objects, such as tables and chairs and trees. We all feel quite sure about these in ordinary life, and yet our reasons for confidence are really very inadequate. Naïve common sense supposes that they are what they appear to be, but that is impossible, since they do not appear exactly alike to any two simultaneous observers; at least, it is impossible if the object is a single thing, the same for all observers. If we are going to admit that the object is not what we see, we can no longer feel the same assurance that there is an object ”

“ Philosophy involves a criticism of scientific knowledge, not from a point of view ultimately different from that of science, but from a point of view less concerned with details and more concerned with the harmony of the whole body of special sciences.
The special sciences have all grown up by the use of notions derived from common sense, such as things and their qualities, space, time, and causation. Science itself has shown that none of these common-sense notions will quite serve for the explanation of the world ”

“ Now physics says that a table or a chair is "really" an incredibly vast system of electrons and protons in rapid motion, with empty space in between. This is all very well. But the physicist, like the ordinary man, is dependent upon his senses for the existence of the physical world. If you go up to him solemnly and say, "Would you be so kind as to tell me, as a physicist, what a chair really is?" ”

“ But if we sometimes hear sentences which have not proceeded from a body, why should this not always be the case? Perhaps our imagination has conjured up all the things that we think others have said to us. But this is part of the general problem of inferring physical objects from sensations, which, difficult as it is, is not the most difficult part of the logical puzzles concerning testimony. The most difficult part is the inference from the policeman's body to his mind. ”

“ Induction raises perhaps the most difficult problem in the whole theory of knowledge. Every scientific law is established by its means, and yet it is difficult to see why we should believe it to be a valid logical process. Induction, in its bare essence, consists of the argument that, because A and B have been often found together and never found apart, therefore, when A is found again, B will probably also be found. This exists first as a "physiological inference", and as such is practised by animals. ”

“ Philosophy arises from an unusually obstinate attempt to arrive at real knowledge. What passes for knowledge in ordinary life suffers from three defects: it is cocksure, vague, and self-contradictory. The first step towards philosophy consists in becoming aware of these defects, not in order to rest content with a lazy scepticism, but in order to substitute an amended kind of knowledge which shall be tentative, precise, and self-consistent. ”

“ Relativity We have seen that the world of the atom is a world of revolution rather than evolution: the electron which has been moving in one orbit hops quite suddenly into another, so that the motion is what is called "discontinuous", that is to say, the electron is first in one place and then in another, without having passed over any intermediate places. This sounds like magic, and there may be some way of avoiding such a disconcerting hypothesis. At any rate, nothing of the sort seems to happen in the regions where there are no electrons and protons. ”

“ But the inference is never clearly set forth in a logical chain, and, if it were, it might not look sufficiently plausible to warrant much confidence. In actual fact, the whole development from common-sense objects to electrons and protons has been governed by certain beliefs, seldom conscious, but existing in every natural man. These beliefs are not unalterable, but they grow and develop like a tree. We start by thinking that a chair is as it appears to be, and is still there when we are not looking. ”

“ Thus we are committed to causation as an a priori belief without which we should have no reason for supposing that there is a "real" chair at all. Also, for the sake of permanence we bring in the notion of substance: the "real" chair is a substance, or collection of substances, possessed of permanence and the power to cause sensations. This metaphysical belief has operated, more or less unconsciously, in the inference from sensations to electrons and protons. The philosopher must drag such beliefs into the light of day, and see whether they still survive. ”

“ Sometimes people suffer from hallucinations, that is to say, they think they perceive physical objects, but are not confirmed in this belief by the testimony of others. In such cases, we decide that they are mistaken. It is the similarity between the perceptions of different people in similar situations that makes us feel confident of the external causation of our perceptions; but for this, whatever naïve beliefs we might have had in physical objects would have been dissipated long ago. Thus memory and testimony are essential to science. ”

“ When mankind took to science, they tried to formulate logical principles justifying this kind of inference. I shall discuss these attempts in later chapters; for the present, I will only say that they seem to me very unsuccessful. I am convinced that induction must have validity of some kind in some degree, but the problem of showing how or why it can be valid remains unsolved. Until it is solved, the rational man will doubt whether his food will nourish him, and whether the sun will rise to-morrow. ”

“ Philosophy, accordingly, is a continuing activity, not some thing in which we can achieve final perfection once for all. In this respect, philosophy has suffered from its association with theology. Theological dogmas are fixed, and are regarded by the orthodox as incapable of improvement. Philosophers have too often tried to produce similarly final systems: they have not been content with the gradual approximations that satisfied men of science. In this they seem to me to have been mistaken. Philosophy should be piecemeal and provisional like science ”

“ The evidence for a physical law, or for any scientific law, always involves both memory and testimony. We have to rely both upon what we remember to have observed on former occasions, and on what others say they have observed. In the very beginnings of science, it may have been possible sometimes to dispense with testimony ”

“ It is the business of philosophy to correct these defects so far as it can, without throwing over knowledge altogether. To be a good philosopher, a man must have a strong desire to know, combined with great caution in believing that he knows ”

“ If the chair is to persist independently of being seen by us, it must be something other than the patch of colour we see, because this is found to depend upon conditions extraneous to the chair, such as how the light falls, whether we are wearing blue spectacles, and so on. This forces the man of science to regard the "real" chair as the cause (or an indispensable part of the cause) of our sensations when we see the chair. ”

“ In "seeing a chair", for instance, we do not first apprehend a coloured pattern, and then proceed to infer a chair: belief in the chair arises spontaneously when we see the coloured pattern. But this belief has causes not only in the present physical stimulus, but also partly in past experience, partly in reflexes. In animals, reflexes play a very large part; in human beings, experience is more important. The infant learns slowly to correlate touch and sight, and to expect others to see what he sees. ”

“ That being so, it is of course necessary to say what strings of events constitute bodies, since not all continuous strings of events do so, nor even all geodesics. Until we have defined the sort of thing that makes a body, we cannot legitimately speak of motion, since this involves the presence of one body on different occasions. We must therefore set to work to define what we mean by the persistence of a body, and how a string of events constituting a body differs from one which does not. ”

“ Both in introspection and in external perception, we try to express what we know in words.
We come here, as in the question of testimony, upon the social aspect of knowledge. The purpose of words is to give the same kind of publicity to thought as is claimed for physical objects. A number of people can hear a spoken word or see a written word, because each is a physical occurrence. ”

“ The inference to the policeman's mind certainly may be wrong. It is clear that a maker of waxworks could make a life-like policeman and put a gramophone inside him, which would cause him periodically to tell visitors the way to the most interesting part of the exhibition at the entrance to which he would stand. They would have just the sort of evidence of his being alive that is found convincing in the case of other policemen. Descartes believed that animals have no minds, but are merely complicated automata. Eighteenth-century materialists extended this doctrine to men. ”

“ The habits which are thus formed are essential to our adult notion of an object such as a chair. The perception of a chair by means of sight has a physical stimulus which affects only sight directly, but stimulates ideas of solidity and so on through early experience. The inference might be called "physiological". ”

“ They will not arrive at the same estimate for the distance in space or the lapse of time between the two events, but the interval is a genuine physical fact, the same for all. If a body can travel freely from one event to the other, the interval between the two events will be the same as the time between them as measured by a clock travelling with the body. If such a journey is physically impossible, the interval will be the same as the distance as estimated by an observer to whom the two events are simultaneous. ”

“ So long as we continue to think in terms of bodies moving, and try to adjust this way of thinking to the new ideas by successive corrections, we shall only get more and more confused. The only way to get clear is to make a fresh start, with events instead of bodies. ”

“ And even if we cannot be completely rational, we should probably all be the better for becoming somewhat more rational than we are. At the lowest estimate, it will be an interesting adventure to see whither reason will lead us. ”

“ An event at one moment is succeeded by an event at a neighbouring moment, which, to the first order of small quantities, can be calculated from the earlier event. This enables us to construct a string of events, each, approximately, growing out of a slightly earlier event according to an intrinsic law. Outside influences only affect the second order of small quantities. A string of events connected, in this way, by an approximate intrinsic law of development is called one piece of matter. This is what I mean by saying that the unity of a piece of matter is causal. ”

“ When we first begin to reflect, we find ourselves making inductions in the physiological sense, for instance, expecting the food we see to have a certain kind of taste. Often we only become aware of this expectation through having it disappointed, for instance if we take salt thinking it is sugar. ”

“ Therefore the first step in defining "philosophy" is the indication of these problems and doubts, which is also the first step in the actual study of philosophy. There are some among the traditional problems of philosophy that do not seem to me to lend themselves to intellectual treatment, because they transcend our cognitive powers ”

“ A straight line, for example, is supposed to be a certain track in space whose parts all exist simultaneously. We shall now find that what is a straight line for one observer is not a straight line for another. ”

“ The effect of our passions upon our beliefs forms a favourite subject of modern psychologists; but the converse effect, that of our beliefs upon our passions, also exists, though it is not such as an old-fashioned intellectualist psychology would have supposed. ”

“ There are others, however, as to which, even if a final solution is not possible at present, yet much can be done to show the direction in which a solution is to be sought, and the kind of solution that may in time prove possible. ”