Philosophy

Everything in the world is composed of “events”; that, at least, is the thesis I wish to maintain. An “event”, as I understand it, is something having a small finite duration and a small finite extension in space; or rather, in view of the theory of relativity, it is something occupying a small finite amount of space-time. If it has parts, these parts, I say, are again events, never something occupying a mere point of instant, whether in space, in time, or in space-time. The fact that an event occupies a finite amount of space-time does not prove that it has parts. Events are not impenetrable, as matter is supposed to be; on the contrary, every event in space-time is overlapped by other events. There is no reason to suppose that any of the events with which we are familiar are infinitely complex; on the contrary, everything known about the world is compatible with the view that every complex event has a finite number of parts. We do not know that this is the case, but it is an hypothesis which cannot be refuted and is simpler than any other possible hypothesis. I shall therefore adopt it as a working hypothesis in what follows.

When I speak of an “event” I do not mean anything out of the way. Seeing a flash of lightning is an event; so is hearing a tire burst, or smelling a rotten egg, or feeling the coldness of a frog. These are events that are “data” in the sense of Chapter XXV; but, on the principles explained in that chapter, we infer that there are events which are not data and happen at a distance from our own body. Some of these are data to other people, others are data to no one. In the case of the flash of lightning, there is an electro-magnetic disturbance consisting of events travelling outward from the place where the flash takes place, and then when this disturbance reaches the eye of a person or animal that can see, there is a percept, which is causally continuous with the events between the place of the lightning and the body of the percipient. Percepts afford the logical premisses for all inferences to events that are not precepts, wherever such inferences are logically justifiable. Particular colours and sounds and so on are events; their causal antecedents in the inanimate world are also events.

If we assume, as I propose to do, that every event has only a finite number of parts, then every event is composed of a finite number of events that have no parts. Such events I shall call “minimal events.” It will simplify our discussion to assume them, but by a little circumlocution this assumption could be eliminated. The reader must not therefore regard it as an essential part of what follows.

A minimal event occupies a finite region in space-time. Let us take time alone for purposes of illustration. The event in question may overlap in time with each of two others, although the first of these others wholly precedes the second; for example, you may hear a long note on the violin while you hear two short notes on the piano. (It is not necessary to suppose that these are really minimal events; I merely want to illustrate what is meant.) I assume that every event is contemporaneous with events that are not contemporaneous with each other; this is what is meant by saying that every event lasts for a finite time, as the reader can easily convince himself if he remembers that time is wholly relational. If we look away from the world of physics for a moment, and confine ourselves to the world of one man’s experience, we can easily define an “instant” in his life. It will be a group of events, all belonging to his experience, and having the following two properties: (1) any two of the events overlap; (2) no event outside the group overlaps with every member of the group. By a slightly more complicated but essentially similar method, we can define a point-instant in space-time as a group of events having two properties analogous to those used just now in defining an “instant” in one biography.13 Thus the “points” (or point-instants) that the mathematician needs are not simple, but are structures composed of events, made up for the convenience of the mathematician. There will be many “points” of which a given minimal event is a member; all these together make up the region of space-time occupied by that event. Space-time order, as well as space-time points, results from the relations between events.

A piece of matter, like a space-time point, is to be constructed out of events, but the construction is considerably more complicated, and in the end is only an approximation to what the physicist supposes to be really taking place. There are, at the moment, two somewhat different views of matter, one appropriate to the study of atomic structure, the other to the general theory of relativity as affording an explanation of gravitation. The view appropriate to atomic structure has itself two forms, one derived from Heisenberg, the other from De Broglie and Schrödinger. These two forms, it is true, are mathematically equivalent, but in words they are very different. Heisenberg regards a piece of matter as a centre from which radiations travel outward; the radiations are supposed really to occur, but the matter at their centre is reduced to a mere mathematical fiction. The radiations are, for example, such as constitute light; they are all avowedly systems of events, not changes in the conditions or relations of “substances.” In the De Broglie-Schrödinger system, matter consists of wave motions. It is not necessary to the theory to postulate anything about these wave-motions except their mathematical characteristics, but, obviously, since they are to explain matters they cannot serve their purpose if they consist of motions of matter. In this system also, therefore, we are led to construct matter out of systems of events, which just happen, and do not happen “to” matter or “to” anything else.

Gravitation, as explained by the general theory of relativity, is reduced to “crinkles” in space-time. Space-time being, as we have already seen, a system constructed out of events, the “crinkles” in it are also derived from events. There is no reason to suppose that there is a “thing” at the place where the “crinkle” is most crinkly. Thus in this part of physics, also, matter has ceased to be a “thing” and has become merely a mathematical characteristic of the relations between complicated logical structures composed of events.

It was traditionally a property of substance to be permanent, and to a considerable extent matter has retained this property in spite of its loss of substantiality. But its permanence now is only approximate, not absolute. It is thought that an electron and a proton can meet and annihilate each other; in the stars this is supposed to be happening on a large scale.14 And even while an electron or a proton lasts, it has a different kind of persistence from that formerly attributed to matter. A wave in the sea persists for a longer or shorter time: the waves that I see dashing themselves to pieces on the Cornish coast may have come all the way from Brazil, but that does not mean that a “thing” has travelled across the Atlantic; it means only that a certain process of change has travelled. And just as a wave in the sea comes to grief at last on the rocks, so an electron or a proton may come to grief when it meets some unusual state of affairs.

Thus “matter” has very definitely come down in the world as a result of recent physics. It used to be the cause of our sensations: Dr. Johnson “disproved” Berkeley’s denial of matter by kicking a stone. If he had known that his foot never touched the stone, and that both were only complicated systems of wave-motions, he might have been less satisfied with his refutation. We cannot say that “matter” is the cause of our sensations. We can say that the events which cause our sensations usually belong to the sort of group that physicists regard as material; but that is a very different thing. Impenetrability used to be a noble property of matter, a kind of Declaration of Independence; now it is a merely tautological result of the way in which matter is defined. The events which are the real stuff of the world are not impenetrable, since they can overlap in space-time. In a word, “matter” has become no more than a convenient shorthand for stating certain causal laws concerning events.

But if matter has fared badly, mind has fared little better. The adjective “mental” is one which is not capable of any exact significance. There is, it is true, an important group of events, namely percepts, all of which may be called “mental”. But it would be arbitrary to say that there are no “mental” events except percepts, and yet it is difficult to find any principle by which we can decide what other events should be included. Perhaps the most essential characteristics of mind are introspection and memory. But memory in some of its forms is, as we have seen, a consequence of the law of conditioned reflexes, which is at least as much physiological as psychological, and characterises living tissue rather than mind. Knowledge, as we have found, is not easy to distinguish from sensitivity, which is a property possessed by scientific instruments. Introspection is a form of knowledge, but turns out, on examination, to be little more than a cautious interpretation of ordinary “knowledge”. Where the philosopher’s child at the Zoo says “There is a hippopotamus over there”, the philosopher should reply: “There is a coloured pattern of a certain shape, which may perhaps be connected with a system of external causes of the sort called a hippopotamus”. (I do not live up to this precept myself.) In saying that there is a coloured pattern, the philosopher is practising introspection in the only sense that I can attach to that term, i.e. his knowledge-reaction is to an event situated in his own brain from the standpoint of physical space, and is consciously avoiding physiological and other inference as far as possible. Events to which a knowledge-reaction of this sort occurs are “mental”; so are, presumably, other events resembling them in certain respects. But I do not see any way of defining this wider group except by saying that mental events are events in a living brain, or, better, in a region combining sensitivity and the law of learned reactions to a marked extent. This definition has at least the merit of showing that mentality is an affair of causal laws, not of the quality of single events, and also that mentality is a matter of degree.

Perhaps it is not unnecessary to repeat, at this point, that events in the brain are not to be regarded as consisting of motions of bits of matter. Matter and motion, as we have seen, are logical constructions using events as their material, and events are therefore something quite different from matter in motion. I take it that, when we have a percept, just what we perceive (if we avoid avoidable sources of error) is an event occupying part of the region which, for physics, is occupied by the brain. In fact, perception gives us the most concrete knowledge we possess as to the stuff of the physical world, but what we perceive is part of the stuff of our brains, not part of the stuff of tables and chairs, sun, moon, and stars. Suppose we are looking at a leaf, and we see a green patch. This patch is not “out there” where the leaf is, but is an event occupying a certain volume in our brains during the time that we see the leaf. Seeing the leaf consists of the existence, in the region occupied by our brain, of a green patch causally connected with the leaf, or rather with a series of events emanating from the place in physical space where physics places the leaf. The percept is one of this series of events, differing from the others in its effects owing to the peculiarities of the region in which it occurs—or perhaps it would be more correct to say that the different effects are the peculiarities of the region.

Thus “mind” and “mental” are merely approximate concepts, giving a convenient shorthand for certain approximate laws. In a completed science, the word “mind” and the word “matter” would both disappear, and would be replaced by causal laws concerning “events”, the only events known to us otherwise than in their mathematical and causal properties being percepts, which are events situated in the same region as a brain and having effects of a peculiar sort called “knowledge-reactions”.

It will be seen that the view which I am advocating is neither materialism nor mentalism, but what we call “neutral monism”. It is monism in the sense that it regards the world as composed of only one kind of stuff, namely events; but it is pluralism in the sense that it admits the existence of a great multiplicity of events, each minimal event being a logically self-subsistent entity.

There is, however, another question, not quite the same as this, namely the question as to the relations of psychology and physics. If we knew more, would psychology be absorbed in physics? or, conversely, would physics be absorbed in psychology? A man may be a materialist and yet hold that psychology is an independent science; this is the view taken by Dr. Broad in his important book on The Mind and its Place in Nature. He holds that a mind is a material structure, but that it has properties which could not, even theoretically, be inferred from those of its material constituents. He points out that structures very often have properties which, in the present state of our knowledge, cannot be inferred from the properties and relations of their parts. Water has many properties which we cannot infer from those of hydrogen and oxygen, even if we suppose ourselves to know the structure of the molecule of water more completely than we do as yet. Properties of a whole which cannot, even theoretically, be inferred from the properties and relations of its parts are called by Dr. Broad “emergent” properties. Thus he holds that a mind (or brain) has properties which are “emergent”, and to this extent psychology will be independent of physics and chemistry. The “emergent” properties of minds will only be discoverable by observation of minds, not by inference from the laws of physics and chemistry. This possibility is an important one, and it will be worth while to consider it.

Our decision to regard a unit of matter as itself not ultimate, but an assemblage of events, somewhat alters the form of our question as to “emergent” properties. We have to ask: Is matter emergent from events? Is mind emergent from events? If the former, is mind emergent from matter, or deducible from the properties of matter, or neither? If the latter, is matter emergent from mind or deducible from the properties of mind, or neither? Of course, if neither mind nor matter is emergent from events, these latter questions do not arise.

Let us coin a word, “chrono-geography”, for the science which begins with events having space-time relations and does not assume at the outset that certain strings of them can be treated as persistent material units or as minds. Then we have to ask ourselves first: can the science of matter, as it appears in physics and chemistry, be wholly reduced to chrono-geography? If no, matter is emergent from events; if yes, it is not emergent.

Is matter emergent from events? In the present state of science it is difficult to give a decided answer to this question. The notion of matter, in modern physics, has become absorbed into the notion of energy. Eddington, in his Mathematical Theory of Relativity shows that, in virtue of the laws assumed concerning events, there must be something having the observed properties of matter and energy as regards conservation. This he calls the “material-energy-tensor”, and suggests that it is the reality which we sometimes call “matter” and sometimes “energy”. To this extent, matter has been shown to be not emergent. But the existence of electrons and protons (to the extent that they do exist) has not yet been deduced from the general theory of relativity, though attempts are being made and may at any moment succeed. If and when these attempts succeed, physics will cease to be in any degree independent of chrono-geography, but for the present it remains in part independent. As for chemistry, although we cannot practically reduce it all to physics, we can see how, theoretically, this could be done, and I think it is safe to assume that it is not an ultimately independent science.

The question we have been asking is: could we predict, theoretically, from the laws of events that there must be material units obeying the laws which they do in fact obey, or is this a new, logically independent, fact? In theory we might be able to prove that it is not independent, but it would be very difficult to prove that it is. The present position is, broadly speaking, that the continuous properties of the physical world can be deduced from chrono-geography, but not the discontinuous facts, viz. electrons and protons and Planck’s quantum. Thus for the present materiality is practically, though perhaps not theoretically, an emergent characteristic of certain groups of events.

Is mind emergent from events? This question, as yet, can hardly be even discussed intelligently, because psychology is not a sufficiently advanced science. There are, nevertheless, some points to be noted. Chrono-geography is concerned only with the abstract mathematical properties of events, and cannot conceivably, unless it is radically transformed, prove that there are visual events, or auditory events, or events of any of the kinds that we know by perception. In this sense, psychology is certainly emergent from chrono-geography and also from physics, and it is hard to see how it can ever cease to be so. The reason for this is that our knowledge of data contains features of a qualitative sort, which cannot be deduced from the merely mathematical features of the space-time events inferred from data, and yet these abstract mathematical features are all that we can legitimately infer.

The above argument decides also that mind must be emergent from matter, if it is a material structure. No amount of physics can ever tell us all that we do in fact know about our own percepts.

We have still to ask whether we are to regard a mind as a structure of material units or not. If we do so regard it, we are, so far as mind is concerned, emergent materialists in view of what we have just decided; this is the view favoured by Dr. Broad. If we do not so regard it, we are in no sense materialists. In favour of the materialist view, there is the fact that, so far as our experience goes, minds only emerge in connection with certain physical structures, namely living bodies, and that mental development increases with a certain kind of complexity of physical structure. We cannot set against this the argument that minds have peculiar characteristics, for this is quite consistent with emergent materialism. If we are to refute it, it must be by finding out what sort of group of events constitutes a mind. It is time to address ourselves to this question.

What is a mind? It is obvious, to begin with, that a mind must be a group of mental events, since we have rejected the view that it is a single simple entity such as the ego was formerly supposed to be. Our first step, therefore, is to be clear as to what we mean by a “mental” event.

We said a few pages ago that: Mental events are events in a region combining sensitivity and the law of learned reactions to a marked extent. For practical purposes, this means (subject to a proviso to be explained shortly) that a mental event is any event in a living brain. We explained that this does not mean that a mental event consists of matter in motion, which is what an old-fashioned physicist would regard as the sort of event that happens in a brain. Matter in motion, we have seen, is not an event in our sense, but a shorthand description of a very complicated causal process among events of a different sort. But we must say a few words in justification of our definition.

Let us consider some alternative definitions. A mental event, we might say, is one which is “experienced.” When is an event “experienced”? We might say: when it has “mnemic” effects, i.e. effects governed by the law of association. But we saw that this law applies to purely bodily events such as the contraction of the pupil, with which nothing “mental” seems to be connected. Thus if our definition is to serve, we shall have to define “experience” differently; we shall have to say that the mnemic effects must include something that can be called “knowledge.” This would suggest the definition: A mental event is anything that is remembered. But this is too narrow: we only remember a small proportion of our mental events. We might have regarded “consciousness” as the essence of mental events, but this view was examined and found inadequate in Chapter XX. Moreover, we do not want our definition to exclude the “unconscious”.

It is clear that the primary mental events, those about which there can be no question, are percepts. But percepts have certain peculiar causal properties, notably that they give rise to knowledge-reactions, and that they are capable of having mnemic effects which are cognitions. These causal properties, however, belong to some events which are not apparently percepts. It seems that any event in the brain may have these properties. And perhaps we were too hasty in saying that the contraction of the pupil on hearing a loud noise involves nothing “mental”. There may be other “mental” events connected with a human body besides those belonging to the central personality. I shall come back to this possibility presently. Meanwhile, I shall adhere to the above definition of a “mental” event, which, as we saw, makes mentality a matter of degree.

We can now return to the question: What is a mind? There may be mental events not forming part of the sort of group that we should call a “mind”, but there certainly are groups having that kind of unity that make us call them one mind. There are two marked characteristics of a mind: First, it is connected with a certain body; secondly, it has the unity of one “experience”. The two prima facie diverge in cases of dual or multiple personality, but I think this is more apparent than real. These two characteristics are, one physical, the other psychological. Let us consider each in turn as a possible definition of what we mean by one “mind”.

In the physical way, we begin by observing that every mental event known to us is also part of the history of a living body, and we define a “mind” as the group of mental events which form part of the history of a certain living body. The definition of a living body is chemical, and the reduction of chemistry to physics is clear in theory, though in practice the mathematics is too difficult. It is so far a merely empirical fact that mnemic causation is almost exclusively associated with matter having a certain chemical structure. But the same may be said of magnetism. As yet, we cannot deduce the magnetic properties of iron from what we know of the structure of the atom of iron, but no one doubts that they could be deduced by a person with sufficient knowledge and sufficient mathematical skill. In like manner it may be assumed that mnemic causation is theoretically deducible from the structure of living matter. If we knew enough, we might be able to infer that some other possible structure would exhibit mnemic phenomena, perhaps in an even more marked degree; if so, we might be able to construct Robots who would be more intelligent than we are.

In the psychological way of defining a “mind”, it consists of all the mental events connected with a given mental event by “experience”, i.e. by mnemic causation, but this definition needs a little elaboration before it can be regarded as precise. We do not want the contraction of the pupil to count as a “mental” event; therefore a mental event will have to be one which has mnemic effects, not merely mnemic causes. In that case, however, there cannot be a last mental event in a man’s life, unless we assume that it may have mnemic effects on his body after death. Perhaps we may avoid this inconvenience by discovering the kind of event that usually has mnemic effects, though they may be prevented from occurring by special circumstances. Or we might maintain that death is gradual, even when it is what is called instantaneous; in that case the last events in a man’s life grow progressively less mental as life ebbs. Neglecting this point, which is not very important, we shall define the “experience” to which a given mental event belongs as all those mental events which can be reached from the given event by a mnemic causal chain, which may go backwards or forwards, or alternately first one and then the other. This may be conceived on the analogy of an engine shunting at a junction or where there are many points: any line that can be reached, by however many shuntings, will count as part of the same experience.

We cannot be sure that all the mental events connected with one body are connected by links of mnemic causation with each other, and therefore we cannot be sure that our two definitions of one “mind” give the same result. In cases of multiple personality, some at least of the usual mnemic effects, notably recollection, are absent in the life of one personality when they have occurred in the life of the other. But probably both personalities are connected by mnemic chains with events which occurred before the dissociation took place, so that there would be only one mind according to our definition. But there are other possibilities which must be considered. It may be that each cell in the body has its own mental life, and that only selections from these mental lives go to make up the life which we regard as ours. The “unconscious” might be the mental lives of subordinate parts of the body, having occasional mnemic effects which we can notice, but in the main separate from the life of which we are “conscious”. If so, the mental events connected with one body will be more numerous than the events making up its central “mind”. These, however, are only speculative possibilities.

I spoke a moment ago of the life of which we are “conscious”, and perhaps the reader has been wondering why I have not made more use of the notion of “consciousness”. The reason is that I regard it as only one kind of mnemic effect, and not one entitled to a special place. To say that I am “conscious” of an event is to say that I recollect it, at any rate for a short time after it has happened. To say that I recollect an event is to say that a certain event is occurring in me now which is connected by mnemic causation with the event recollected, and is of the sort that we call a “cognition” of that event. But events which I do not recollect may have mnemic effects upon me. This is the case, not only where we have Freudian suppression, but in all habits which were learnt long ago and have now become automatic, such as writing and speaking. The emphasis upon consciousness has made a mystery of the “unconscious”, which ought to be in no way surprising.

It does not much matter which of our two definitions of a “mind” we adopt. Let us, provisionally, adopt the first definition, so that a mind is all the mental events which form part of the history of a certain living body, or perhaps we should rather say a living brain.

We can now tackle the question which is to decide whether we are emergent materialists or not, namely:

Is a mind a structure of material units?

I think it is clear that the answer to this question is in the negative. Even if a mind consists of all the events in a brain, it does not consist of bundles of these events grouped as physics groups them, i.e. it does not lump together all the events that make up one piece of matter in the brain, and then all the events that make up another, and so on. Mnemic causation is what concerns us most in studying mind, but this seems to demand a recourse to physics, if we assume, as seems plausible, that mental mnemic causation is due to effects upon the brain. This question, however, is still an open one. If mnemic causation is ultimate, mind is emergent. If not, the question is more difficult. As we saw earlier, there certainly is knowledge in psychology which cannot ever form part of physics. But as this point is important, I shall repeat the argument in different terms.

The difference between physics and psychology is analogous to that between a postman’s knowledge of letters and the knowledge of a recipient of letters. The postman knows the movements of many letters, the recipient knows the contents of a few. We may regard the light and sound waves that go about the world as letters of which the physicist may know the destination; some few of them are addressed to human beings, and when read give psychological knowledge. Of course the analogy is not perfect, because the letters with which the physicist deals are continually changing during their journeys, as if they were written in fading ink, which, also, was not quite dry all the time, but occasionally got smudged with rain. However, the analogy may pass if not pressed.

It would be possible without altering the detail of previous discussions, except that of Chapter XXV, to give a different turn to the argument, and make matter a structure composed of mental units. I am not quite sure that this is the wrong view. It arises not unnaturally from the argument as to data contained in Chapter XXV. We saw that all data are mental events in the narrowest and strictest sense, since they are percepts. Consequently all verification of causal laws consists in the occurrence of expected percepts. Consequently any inference beyond percepts (actual or possible) is incapable of being empirically tested. We shall therefore be prudent if we regard the non-mental events of physics as mere auxiliary concepts, not assumed to have any reality, but only introduced to simplify the laws of percepts. Thus matter will be a construction built out of percepts, and our metaphysic will be essentially that of Berkeley. If there are no non-mental events, causal laws will be very odd; for example, a hidden dictaphone may record a conversation although it did not exist at the time, since no one was perceiving it. But although this seems odd, it is not logically impossible. And it must be conceded that it enables us to interpret physics with a smaller amount of dubious inductive and analogical inference than is required if we admit non-mental events.

In spite of the logical merits of this view, I cannot bring myself to accept it, though I am not sure that my reasons for disliking it are any better than Dr. Johnson’s. I find myself constitutionally incapable of believing that the sun would not exist on a day when he was everywhere hidden by clouds, or that the meat in a pie springs into existence at the moment when the pie is opened. I know the logical answer to such objections, and qua logician I think the answer a good one. The logical argument, however, does not even tend to show that there are not non-mental events; it only tends to show that we have no right to feel sure of their existence. For my part, I find myself in fact believing in them in spite of all that can be said to persuade me that I ought to feel doubtful.

There is an argument, of a sort, against the view we are considering. I have been assuming that we admit the existence of other people and their perceptions, but question only the inference from perceptions to events of a different kind. Now there is no good reason why we should not carry our logical caution a step further. I cannot verify a theory by means of another man’s perceptions, but only by means of my own. Therefore the laws of physics can only be verified by me in so far as they lead to predictions of my percepts. If then, I refuse to admit non-mental events because they are not verifiable, I ought to refuse to admit mental events in every one except myself, on the same ground. Thus I am reduced to what is called “solipsism”, i.e. the theory that I alone exist. This is a view which is hard to refute, but still harder to believe. I once received a letter from a philosopher who professed to be a solipsist, but was surprised that there were no others! Yet this philosopher was by way of believing that no one else existed. This shows that solipsism is not really believed even by those who think they are convinced of its truth.

We may go a step further. The past can only be verified indirectly, by means of its effects in the future; therefore the type of logical caution we have been considering should lead us to abstain from asserting that the past really occurred: we ought to regard it as consisting of auxiliary concepts convenient in stating the laws applicable to the future. And since the future, though verifiable if and when it occurs, is as yet unverified, we ought to suspend judgment about the future also. If we are not willing to go so far as this, there seems no reason to draw the line at the precise point where it was drawn by Berkeley. On these grounds I feel no shame in admitting the existence of non-mental events such as the laws of physics lead us to infer. Nevertheless, it is important to realise that other views are tenable.