George Berkeley (1685–1753) is important in philosophy through his denial of the existence of matter—a denial which he supported by a number of ingenious arguments. He maintained that material objects only exist through being perceived. To the objection that, in that case, a tree, for instance, would cease to exist if no one was looking at it, he replied that God always perceives everything; if there were no God, what we take to be material objects would have a jerky life, suddenly leaping into being when we look at them; but as it is, owing to God's perceptions, trees and rocks and stones have an existence as continuous as common sense supposes. This is, in his opinion, a weighty argument for the existence of God. A limerick by Ronald Knox, with a reply, sets forth Berkeley's theory of material objects:
There was a young man who said, 'God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one about in the Quad.'
Your astonishment's odd:
I am always about in the Quad.
And that's why the tree
Will continue to be,
Since observed by
Berkeley was an Irishman, and became a Fellow of Trinity College, Dublin, at the age of twenty-two. He was presented at court by Swift, and Swift's Vanessa left him half her property. He formed a scheme for a college in the Bermudas, with a view to which he went to America; but after spending three years (1728–31) in Rhode Island, he came home and relinquished the project. He was the author of the well-known line:
Westward the course of empire takes its way.
on account of which the town of Berkeley in California was called after him. In 1734 he became Bishop of Cloyne. In later life he abandoned philosophy for tar-water, to which he attributed marvellous medicinal properties. It was concerning tar-water that he wrote: 'These are the cups that cheer, but do not inebriate'—a sentiment more familiar as subsequently applied by Cowper to tea.
All his best work was done while he was still quite young: A New Theory of Vision in 1709, The Principles of Human Knowledge in 1710. The Dialogues of Hylas and Philonous in 1713. His writings after the age of twenty-eight were of less importance. He is a very attractive writer, with a charming style.
His argument against matter is most persuasively set forth in The Dialogues of Hylas and Philonous. Of these dialogues I propose to consider only the first and the very beginning of the second, since everything that is said after that seems to me of minor importance. In the portion of the work that I shall consider, Berkeley advances valid arguments in favour of a certain important conclusion, though not quite in favour of the conclusion that he thinks he is proving. He thinks he is proving that all reality is mental; what he is proving is that we perceive qualities, not things, and that qualities are relative to the percipient.
I shall begin with an uncritical account of what seems to me important in the Dialogues; I shall then embark upon criticism; and finally I shall state the problems concerned as they appear to me.
The characters in the Dialogues are two: Hylas, who stands for scientifically educated common sense; and Philonous, who is Berkeley.
After a few amiable remarks, Hylas says that he has heard strange reports of the opinions of Philonous, to the effect that he does not believe in material substance. 'Can anything,' he exclaims, 'be more fantastical, more repugnant to Common Sense, or a more manifest piece of Scepticism, than to believe there is no such thing as matter?' Philonous replies that he does not deny the reality of sensible things, i.e. of what is perceived immediately by the senses, but that we do not see the causes of colours or hear the causes of sounds. Both agree that the senses make no inferences. Philonous points out that by sight we perceive only light, colour, and figure; by hearing, only sounds; and so on. Consequently, apart from sensible qualities there is nothing sensible, and sensible things are nothing but sensible qualities or combinations of sensible qualities.
Philonous now sets to work to prove that 'the reality of sensible things consists in being perceived', as against the opinion of Hylas, that 'to exist is one thing, and to be perceived is another'. That sense-data are mental is a thesis which Philonous supports by a detailed examination of the various senses. He begins with heat and cold. Great heat, he says, is a pain, and must be in a mind. Therefore heat is mental; and a similar argument applies to cold. This is reinforced by the famous argument about the lukewarm water. When one of your hands is hot and the other cold, you put both into lukewarm water, which feels cold to one hand and hot to the other; but the water cannot be at once hot and cold. This finishes Hylas, who acknowledges that 'heat and cold are only sensations existing in our minds'. But he points out hopefully that other sensible qualities remain.
Philonous next takes up tastes. He points out that a sweet taste is a pleasure and a bitter taste is a pain, and that pleasure and pain are mental. The same argument applies to odours, since they are pleasant or unpleasant.
Hylas makes a vigorous effort to rescue sound, which, he says, is motion in air, as may be seen from the fact that there are no sounds in a vacuum. We must, he says, 'distinguish between sound as it is perceived by us, and as it is in itself; or between the sound which we immediately perceive and that which exists without us'. Philonous points out that what Hylas calls 'real' sound, being a movement, might possibly be seen or felt, but can certainly not be heard; therefore it is not sound as we know it in perception. As to this, Hylas now concedes that 'sounds too have no real being without the mind'.
They now come to colours, and here Hylas begins confidently: 'Pardon me: the case of colours is very different. Can anything be plainer than that we see them on the objects?' Substances existing without the mind, he maintains, have the colours we see on them. But Philonous has no difficulty in disposing of this view. He begins with the sunset clouds, which are red and golden, and points out that a cloud, when you are close to it, has no such colours. He goes on to the difference made by a microscope, and to the yellowness of everything to a man who has jaundice. And very small insects, he says, must be able to see much smaller objects than we can see. Hylas thereupon says that colour is not in the objects, but in the light; it is, he says, a thin fluid substance. Philonous points out, as in the case of sound, that, according to Hylas, 'real' colours are something different from the red and blue that we see, and that this won't do.
Hereupon Hylas gives way about all secondary qualities, but continues to say that primary qualities, notably figure and motion, are inherent in external unthinking substances. To this Philonous replies that things look big when we are near them and small when we are far off, and that a movement may seem quick to one man and slow to another.
At this point Hylas attempts a new departure. He made a mistake, he says, in not distinguishing the object from the sensation; the act of perceiving he admits to be mental, but not what is perceived; colours, for example, 'have a real existence without the mind, in some unthinking substance'. To this Philonous replies: 'That any immediate object of the senses—that is, any idea or combination of ideas—should exist in an unthinking substance, or exterior to all minds, is in itself an evident contradiction.' It will be observed that, at this point, the argument becomes logical and is no longer empirical. A few pages later, Philonous says: 'Whatever is immediately perceived is an idea; and can any idea exist out of the mind?'
After a metaphysical discussion of substance, Hylas returns to the discussion of visual sensations, with the argument that he sees things at a distance. To this Philonous replies that this is equally true of things seen in dreams, which everyone admits to be mental; further, that distance is not perceived by sight, but judged as the result of experience, and that, to a man born blind but now for the first time able to see, visual objects would not appear distant.
At the beginning of the second Dialogue, Hylas urges that certain traces in the brain are the causes of sensations, but Philonous retorts that 'the brain, being a sensible thing, exists only in the mind'.
The remainder of the Dialogues is less interesting, and need not be considered.
Let us now make a critical analysis of Berkeley's contentions.
Berkeley's argument consists of two parts. On the one hand, he argues that we do not perceive material things, but only colours, sounds, etc., and that these are 'mental' or 'in the mind'. His reasoning is completely cogent as to the first point, but as to the second it suffers from the absence of any definition of the word 'mental'. He relies, in fact, upon the received view that everything must be either material or mental, and that nothing is both.
When he says that we perceive qualities, not 'things' or 'material substances', and that there is no reason to suppose that the different qualities which common sense regards as all belonging to one 'thing' inhere in a substance distinct from each and all of them, his reasoning may be accepted. But when he goes on to say that sensible qualities—including primary qualities—are 'mental', the arguments are of very different kinds, and of very different degrees of validity. There are some attempting to prove logical necessity, while others are more empirical. Let us take the former first.
Philonous says: 'Whatever is immediately perceived is an idea: and can any idea exist out of the mind?' This would require a long discussion of the word 'idea'. If it were held that thought and perception consist of a relation between subject and object, it would be possible to identify the mind with the subject, and to maintain that there is nothing 'in' the mind, but only objects 'before' it. Berkeley discusses the view that we must distinguish the act of perceiving from the object perceived, and that the former is mental while the latter is not. His argument against this view is obscure, and necessarily so, since, for one who believes in mental substance, as Berkeley does, there is no valid means of refuting it. He says: 'That any immediate object of the senses should exist in an unthinking substance, or exterior to all minds, is in itself an evident contradiction.' There is here a fallacy, analogous to the following: 'It is impossible for a nephew to exist without an uncle; now Mr A is a nephew; therefore it is logically necessary for Mr A to have an uncle.' It is, of course, logically necessary given that Mr A is a nephew, but not from anything to be discovered by analysis of Mr A. So, if something is an object of the senses, some mind is concerned with it; but it does not follow that the same thing could not have existed without being an object of the senses.
There is a somewhat analogous fallacy as regards what is conceived. Hylas maintains that he can conceive a house which no one perceives, and which is not in any mind. Philonous retorts that whatever Hylas conceives is in his mind, so that the supposed house is, after all, mental. Hylas should have answered: 'I do not mean that I have in mind the image of a house; when I say that I can conceive a house which no one perceives, what I really mean is that I can understand the proposition "there is a house which no one perceives", or, better still, "there is a house which no one either perceives or conceives".' This proposition is composed entirely of intelligible words, and the words are correctly put together. Whether the proposition is true or false, I do not know; but I am sure that it cannot be shown to be self-contradictory. Some closely similar propositions can be proved. For instance: the number of possible multiplications of two integers is infinite, therefore there are some that have never been thought of. Berkeley's argument, if valid, would prove that this is impossible.
The fallacy involved is a very common one. We can, by means of concepts drawn from experience, construct statements about classes some or all of whose members are not experienced. Take some perfectly ordinary concept, say 'pebble'; this is an empirical concept derived from perception. But it does not follow that all pebbles are perceived, unless we include the fact of being perceived in our definition of 'pebble'. Unless we do this, the concept 'unperceived pebble' is logically unobjectionable, in spite of the fact that it is logically impossible to perceive an instance of it.
Schematically, the argument is as follows. Berkeley says: 'Sensible objects must be sensible. A is a sensible object. Therefore A must be sensible.' But if 'must' indicates logical necessity, the argument is only valid if A must be a sensible object. The argument does not prove that, from the properties of A other than its being sensible, it can be deduced that A is sensible. It does not prove, for example, that colours intrinsically indistinguishable from those that we see may not exist unseen. We may believe on physiological grounds that this does not occur, but such grounds are empirical; so far as logic is concerned, there is no reason why there should not be colours where there is no eye or brain.
I come now to Berkeley's empirical arguments. To begin with, it is a sign of weakness to combine empirical and logical arguments, for the latter, if valid, make the former superfluous.1 If I am contending that a square cannot be round, I shall not appeal to the fact that no Square in any known city is round. But as we have rejected the logical arguments, it becomes necessary to consider the empirical arguments on their merits.
The first of the empirical arguments is an odd one: That heat cannot be in the object, because 'the most vehement and intense degree of heat [is] a very great pain' and we cannot suppose 'any unperceiving thing capable of pain or pleasure'. There is an ambiguity in the word 'pain', of which Berkeley takes advantage. It may mean the painful quality of a sensation, or it may mean the sensation that has this quality. We say a broken leg is painful, without implying that the leg is in the mind; it might be, similarly, that heat causes pain, and that this is all we ought to mean when we say it is a pain. This argument, therefore, is a poor one.
The argument about the hot and cold hands in lukewarm water, strictly speaking, would only prove that what we perceive in that experiment is not hot and cold, but hotter and colder. There is nothing to prove that these are subjective.
In regard to tastes, the argument from pleasure and pain is repeated: Sweetness is a pleasure and bitterness a pain, therefore both are mental. It is also urged that a thing that tastes sweet when I am well may taste bitter when I am ill. Very similar arguments are used about odours: since they are pleasant or unpleasant, 'they cannot exist in any but a perceiving substance or mind'. Berkeley assumes, here and everywhere, that what does not inhere in matter must inhere in a mental substance, and that nothing can be both mental and material.
The argument in regard to sound is ad hominem. Hylas says that sounds are 'really' motions in the air, and Philonous retorts that motions can be seen or
felt, not heard, so that 'real' sounds are inaudible. This is hardly a fair argument, since percepts of motion, according to Berkeley, are just as subjective as other percepts. The motions that Hylas requires will have to be unperceived and imperceptible. Nevertheless it is valid in so far as it points out that sound, as heard, cannot be identified with the motions of air that physics regards as its cause.
Hylas, after abandoning secondary qualities, is not yet ready to abandon primary qualities, viz. Extension, Figure, Solidity, Gravity, Motion, and Rest. The argument, naturally, concentrates on extension and motion. If things have real sizes, says Philonous, the same thing cannot be of different sizes at the same time, and yet it looks larger when we are near it than when we are far off. And if motion is really in the object, how comes it that the same motion may seem fast to one and slow to another? Such arguments must, I think, be allowed to prove the subjectivity of perceived space. But this subjectivity is physical: it is equally true of a camera, and therefore does not prove that shape is 'mental'. In the second Dialogue Philonous sums up the discussion, so far as it has gone, in the words: 'Besides spirits, all that we know or conceive are our own ideas.' He ought not, of course, to make an exception for spirits, since it is just as impossible to know spirit as to know matter. The arguments, in fact, are almost identical in both cases.
Let us now try to state what positive conclusions we can reach as a result of the kind of argument inaugurated by Berkeley.
Things as we know them are bundles of sensible qualities: a table, for example, consists of its visual shape, its hardness, the noise it emits when rapped, and its smell (if any). These different qualities have certain contiquities in experience, which lead common sense to regard them as belonging to one 'thing', but the concept of 'thing' or 'substance' adds nothing to the perceived qualities, and is unnecessary. So far we are on firm ground.
But we must now ask ourselves what we mean by 'perceiving'. Philonous maintains that, as regards sensible things, their reality consists in their being perceived; but he does not tell us what he means by perception. There is a theory, which he rejects, that perception is a relation between a subject and a percept. Since he believed the ego to be a substance, he might well have adopted this theory; however, he decided against it. For those who reject the notion of a substantial ego, this theory is impossible. What, then, is meant by calling something a 'percept'? Does it mean anything more than that the something in question occurs? Can we turn Berkeley's dictum round, and instead of saying that reality consists in being perceived, say that being perceived consists in being real? However this may be, Berkeley holds it logically possible that there should be unperceived things, since he holds that some real things, viz. spiritual substances, are unperceived. And it seems obvious that, when we say that an event is perceived, we mean something more than that it occurs.
What is this more? One obvious difference between perceived and unperceived events is that the former, but not the latter, can be remembered. Is there any other difference?
Recollection is one of a whole genus of effects which are more or less peculiar to the phenomena that we naturally call 'mental'. These effects are connected with habit. A burnt child fears the fire; a burnt poker does not. The physiologist, however, deals with habit and kindred matters as a characteristic of nervous tissue, and has no need to depart from a physicalist interpretation. In physicalist language, we can say that an occurrence is 'perceived' if it has effects of certain kinds; in this sense we might almost say that a watercourse 'perceives' the rain by which it is deepened, and that a river valley is a 'memory' of former downpours. Habit and memory when described in physicalist terms, are not wholly absent in dead matter; the difference, in this respect, between living and dead matter, is only one of degree.
In this view, to say that an event is 'perceived' is to say that it has effects of certain kinds, and there is no reason, either logical or empirical, for supposing that all events have effects of these kinds.
Theory of knowledge suggests a different standpoint. We start, here, not from finished science, but from whatever knowledge is the ground for our belief in science. This is what Berkeley is doing. Here it is not necessary, in advance, to define a 'percept'. The method, in outline, is as follows. We collect the propositions that we feel we know without inference, and we find that most of these have to do with dated particular events. These events we define as 'percepts'. Percepts, therefore, are those events that we know without inference; or at least, to allow for memory, such events were at some time percepts. We are then faced with the question: Can we, from our own percepts, infer any other events? Here four positions are possible, of which the first three are forms of idealism.
(1) We may deny totally the validity of all inferences from my present percepts and memories to other events. This view must be taken by anyone who confines inference to deduction. Any event, and any group of events, is logically capable of standing alone, and therefore no group of events affords demonstrative proof of the existence of other events. If, therefore, we confine inference to deduction, the known world is confined to those events in our own biography that we perceive—or have perceived, if memory is admitted.
(2) The second position, which is solipsism as ordinarily understood, allows some inference from my percepts, but only to other events in my own biography. Take, for example, the view that, at any moment in waking life, there are sensible objects that we do not notice. We see many things without saying to ourselves that we see them; at least, so it seems. Keeping the eyes fixed in an environment in which we perceive no movement, we can notice various things in succession, and we feel persuaded that they were visible before we noticed them; but before we noticed them they were not data for theory of knowledge. This degree of inference from what we observe is made unreflectingly by everybody, even by those who most wish to avoid an undue extension of our knowledge beyond experience.
(3) The third position—which seems to be held, for instance, by Eddington—is that it is possible to make inferences to other events analogous to those in our own experience, and that, therefore, we have a right to believe that there are, for instance, colours seen by other people but not by ourselves, toothaches felt by other people, pleasures enjoyed and pains endured by other people, and so on, but that we have no right to infer events experienced by no one and not forming part of any 'mind'. This view may be defended on the ground that all inference to events which lie outside my observation is by analogy, and that events which no one experiences are not sufficiently analogous to my data to warrant analogical inferences.
(4) The fourth position is that of common sense and traditional physics, according to which there are, in addition to my own experiences and other people's, also events which no one experiences—for example, the furniture of my bedroom when I am asleep and it is pitch dark. G. E. Moore once accused idealists of holding that trains only have wheels while they are in stations, on the ground that passengers cannot see the wheels while they remain in the train. Common sense refuses to believe that the wheels suddenly spring into being whenever you look, but do not bother to exist when no one is inspecting them. When this point of view is scientific, it bases the inference to unperceived events on causal laws.
I do not propose, at present, to decide between these four points of view. The decision, if possible at all, can only be made by an elaborate investigation of non-demonstrative inference and the theory of probability. What I do propose to do is to point out certain logical errors which have been committed by those who have discussed these questions.
Berkeley, as we have seen, thinks that there are logical reasons proving that only minds and mental events can exist. This view, on other grounds, is also held by Hegel and his followers. I believe this to be a complete mistake. Such a statement as 'there was a time before life existed on this planet', whether true or false, cannot be condemned on grounds of logic, any more than 'there are multiplication sums which no one will have ever worked out'. To be observed, or to be a percept, is merely to have effects of certain kinds, and there is no logical reason why all events should have effects of these kinds.
There is, however, another kind of argument, which, while it does not establish idealism as a metaphysic, does, if valid, establish it as a practical policy. It is said that a proposition which is unverifiable has no meaning; that verification depends upon percepts; and that, therefore, a proposition about anything except actual or possible percepts is meaningless. I think that this view, strictly interpreted, would confine us to the first of the above four theories, and would forbid us to speak about anything that we have not ourselves explicitly noticed. If so, it is a view that no one can hold in practice, which is a defect in a theory that is advocated on practical grounds. The whole question of verification, and its connection with knowledge, is difficult and complex; I will, therefore, leave it on one side for the present.
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'. Everyone 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.