An Examination of Plato's Doctrines Vol 2 (RLE: Plato)

Volume 2 Plato on Knowledge and Reality

I Crombie

• Publisher: Routledge
• Year: 2012
• ISBN:
  9781136215940
• Edition: 1
• Topic: Philosophy
• Subtopic: Political Philosophy

Ian Crombie's impressive volumes provide a comprehensive interpretation of Plato's doctrines. Volume 2 deals with more technical philosophical topics, including the theory of knowledge, philosophy of nature, and the methodology of science and philosophy. Each volume is self-contained.

I

THEORY OF KNOWLEDGE

THE discussion of epistemological questions was begun, I suppose, by the fifth century Sophists and in particular by Protagoras: but there was a good deal left for Plato to contribute. It will be convenient to discuss his contributions mainly in terms of three central concepts, namely aisthêsis (perception or sensation), doxa (belief, opinion, judgment) and epistêmê or gnôsis (knowledge or understanding).

I. AISTHÊSIS

A. The machinery of sensation

Plato was well aware of the difference between a philosopher and a physiologist, and did not feel called upon to offer a physiological account of perception. In the Timaeus however (45–6 and 61–8) Timaeus is made to say how he supposes the senses to work. The account which he offers is of the same type as that which is given by a modern physiologist, though of course the details are very different. It is important to have some idea of the physiological picture which Plato thought probable and we will therefore look briefly at Timaeus’ account of sight (Timaeus 45–6 and 67–8).

There is, then, a certain type of fire which cannot burn—in other words, light. This substance is to be found outside us, and there is also a supply of it inside the body. This internal light flows out through the eye when the eye is surrounded by light outside (it cannot get out at night when the eye is surrounded by darkness). The beam of light which flows out through the eye coalesces with the light straight ahead of it, and forms a sort of solid cone with its point at the eye and its base at the surface of the object which is being looked at. Being solid, this cone of light acts as a sort of rigid body and transmits any motions which there may be at the surface of the object back to the eye of the percipient and thence to his mind. (The movement of this solid cone of light thus does the work of light rays in modern optics in that it stimulates in the eye disturbances which correspond to the disturbances at the surface of the object). The colour of the object seen depends on the size of the particles emitted by the object, particles of different sizes having different effects on the cone of light, and therefore on its effect on the eye.

Plato is not committed to the details of this account, and they are not perfectly clear. But in general the position is that both the percipient and the perceived object must be in a state of activity, the one emitting light through its eyes, the other particles from its surface, and that this activity is not what we see, but the cause of our seeing. Our seeing is a pathêma or something which we undergo when the disturbances set up in the eye are large enough to be transmitted to the psuchê or mind.

When Plato turns to a philosophical discussion of the problems of perception in the Theaetetus he seems, as we shall see, to accept this kind of generalised version of the optics of the Timaeus as the basis from which epistemology must start. Epistemological pictures can be crudely divided into cognitive pictures and causal pictures. According to a cognitive picture we somehow use our senses to find out what things are like. The colours and other sense-properties of things belong to them quite independently of our perceiving them; in perception we discover but in no sense create the properties which things have. According to a causal picture on the other hand our sense-data are simply the results of the stimulation of our sense-organs. The sensible properties of things are therefore joint products of the activities of the sense-organ and of the perceived object; and in that way colours and tastes and so on are partially created (so to speak) by our sense-organs in perception. The colour of a thing is the way in which it affects our senses and the true properties of the thing are those properties, whatever they are, which enable it to affect our senses in that way. A causal picture is commonly adopted by those who take seriously (or, some would say, naïvely) the discoveries of the physiologists; and it is I think important, if we are to understand Plato's attitude to empirical knowledge, to remember that he seems to have taken a causal picture for granted.

To take only one respect in which this may be important: a causal picture enhances what I will call the formal rather than the qualitative aspect of our sensory information. Thus there is a formal correspondence, but no qualitative resemblance, between the shape of the groove in a gramophone record and the sound which comes out of the loudspeaker; a certain type of sound corresponds to a certain pattern of groove, but a high note (for example) is not in any other way like a sharply serrated groove. If our sense-organs are thought of as mechanisms, as gramophones are mechanisms, this might at least make it easier to believe that it is the shapes, sizes, velocities and other “primary qualities” of things which are essential to them as they are in themselves.

(One might illustrate the difference between the causal and the cognitive pictures of perception by the difference between two types of mechanism, a gramophone and a magic lantern. In the case of a gramophone you feed in a series of jolts to a stylus and get out something quite different. In the case of a magic lantern you feed in a picture and get out the same picture enlarged on a screen; the mechanism hardly creates the picture but merely renders it visible to a large audience. If our senses are like magic lanterns, windows or telescopes then clearly the world is very much as it seems; if however our senses are more like gramophones then clearly there is a sense in which we shall be misled if we suppose that they tell us what the world is really like).

B. The epistemological status of sensation (the Theaetetus)

Plato's discussion of aisthêsis or sensation is to be found in one of his most brilliant dialogues, the Theaetetus. In form this dialogue is a search for a Socratic definition of knowledge (epistêmê), and the search is unsuccessful. In practice however the point of writing the dialogue was not to fail to define knowledge, nor to show that it cannot be defined, but to illuminate certain other matters. Perhaps the chief of these is that our knowledge¹ of the external world is not a matter of undergoing sense-data but of interpreting them. This result emerges from a long and complicated discussion which takes the form of distinguishing aisthêsis or sensation (which consists of things which happen to us as a result of the stimulation of our sense-organs) from doxa or judgment (which comes about through the comparison of sense-data with each other and which consists in treating them as manifestations of an external world).

The discussion is, as I say, long and complicated. The section we are concerned with is from 151 to 187. It opens when Theaetetus (having begun by defining knowledge in terms of its instances, and having been told that this is not the proper way to define) says that a man who knows anything perceives or senses it and that therefore knowledge is perception or sensation (aisthêsis).

Socrates’ reaction to this is striking, for he proceeds rapidly to identify this definition firstly with Protagoras’ doctrine that there is no distinction (in terms of truth and falsehood) between illusion and reality, and secondly with Heraclitus’ doctrine that there is no stability in the world (panta rei, or “everything is in flux”).

These identifications seem bold, and the second of them farfetched. In order to understand what is in Socrates’ mind we must remember that Theaetetus’ proposed definition “knowledge is perception” is to be read as an equation, and therefore as entailing both: “Every case of perception is a case of knowledge” and also: “Every case of knowledge is a case of perception.” Now if every perception is a case of knowledge, then evidently there are no illusions, and where there is an empirical disagreement, say between Jones who finds the wind chilly and Smith who finds it warm, both must in a sense be right. On the other hand if every case of knowledge is a case of perception then there must be complete instability and randomness in the world. For if there are constant relations between sense-data, and we can be aware of them, then there are things other than sense-data that we can know, namely the constant relations between them. Therefore if our knowledge consists of nothing but the having of sense-data, these constant relations cannot exist; in other words everything is in flux. It must I think be in this way that Socrates makes Theaetetus’ definition imply the Heraclitean doctrine of flux (though it must be confessed that the connection is not made clear in the text).

We must go into this in rather more detail. Since Plato feels that the Protagorean and the Heraclitean doctrines belong very much (at the least) to the same stable, he does not disentangle them completely and we shall not be able to do so either.

(i) The discussion of Protagoras

Protagoras’ treatise apparently opened with the sonorous aphorism “Man is the measure of all things”, and his “relativism” seems to have boxed the philosophical compass. Whatever seems to a man to be so, is so to that man—whether it is a matter of wine seeming sour, or of an institution seeming unjust. There are unusual sense-data and deplorable opinions but there are no illusions and no false beliefs. Plato seems to imply, however, that this general relativism had its roots in a doctrine of perception according to which nobody ever perceives anything but his own sense-data, and grew from these roots into a universal doctrine. This extension may well have taken place in both of two ways. Firstly Protagoras may have felt that all beliefs that a man holds must in the end be based on his experience, so that differences of opinion about, say, politics, or agriculture derive ultimately from different ways of experiencing the world. Secondly, and perhaps more importantly, the words for seeming in Greek as in English (dokein and phainesthai) are ambiguous in having both a sensory and a non-sensory use. Thus the wine may seem sour in the sense that it tastes sour, or it may seem to be stolen in the sense that it is reasonable to believe that it is stolen. It is possible then that Protagoras began by asserting that all sense-data are in the same ontological boat; the wine really has as many different tastes as there are people to whom it tastes different. It is not the case that the wine is really sweet, though it tastes sour to Jones; rather it is really sweet-to-Smith, sour-to-Jones, tasteless-to-Green and so on. Expressing this in the form “whatever seems to a man is to that man”, Protagoras may have felt obliged to go on to say that all opinions are equally true, just as all sense-data are equally valid, simply because an opinion too is something which “seems to a man”.

However this may be, we can distinguish in Protagoras what we may call his central and his extended thesis, his central thesis being that all reports of immediate perception are equally valid, his extended thesis that all beliefs whatever are equally valid. This distinction Socrates gradually draws in the course of the present discussion.

Theaetetus, then, proposes (151) that knowledge is perception, and Socrates tells him that this amounts to the Protagorean doctrine that man is the measure of all things. This doctrine in turn, he says, rests on the further doctrine that: (a) there are really no individual things having properties of their own (whatever seems to have one property can also seem to have the opposite property); and (b) everything is a product of motion and activity. Thus the whiteness of an object, for example, is “a resultant of the contact of the eyes with the appropriate motion” (153 e 6). Since this can be applied to every property of a thing, the objective existence of things is dissolved away and we are left with a world of sense-data, each private to a given percipient. We know from our own experience that a thing which looks one colour on one occasion may well look another colour on another occasion; a fortiori we can infer that what looks one colour to one man may well look different to another man. There is therefore no reason why any sense-datum should be regarded as more veridical than any other, and thus the distinction between reality and illusion is done away with as Protagoras’ thesis requires.

What has happened is this. Theaetetus has suggested that knowledge is perception. But if that is so then there is truth in every perceptual judgment. Yet perceptual disputes occur; the stone which one man finds warm seems cold to another. Therefore we can only say that both of these perceptual judgments are true, if we say that what each man perceives is private to himself—the warm stone private to the one man, the cold stone private to the other. Each man will be correctly reporting the properties of his private stone. But we cannot have an indefinite number of private physical stones in the same place at the same time. The only way therefore in which this can be rendered plausible is to get rid of the physical stone. If the stone is nothing but a collection of the sense-data which lead us to speak of the stone, then there is no reason why one man's sense-data of the stone should agree with another's. The only physical thing involved in the transaction is some process or other whose interaction with our bodies gives rise to the sense-data which we take to represent the stone to us. Physical things are thus got rid of in favour of physical processes and the sense-data begotten of their interaction. This is justly said to be a Heraclitean conclusion.

We know that Plato was influenced by Heracliteanism in his youth; and according to Aristotle he never fully shook it off. It is not surprising therefore that Socrates goes on (153–5) to find things to say in defence of this doctrine. The first is the general observation that activity is beneficial and sloth harmful; this presumably gives some measure of support to the view that nothing in nature is at rest, since it shows nature to be on the side of activity. More seriously Socrates next observes that if a sense-property such as whiteness were located in the object it is difficult to see how it could ever seem any other colour; while if it were supposed to characterise the visual sense of the percipient he would presumably see white all the time. It seems inevitable to regard the whiteness as a product of the interaction between the object and the percipient. These arguments are of some weight and as Plato produces no answer to them it is natural to suppose that he accepted the sense-datum theory to which he makes them point. Then finally Socrates is made to observe that the conventional view that properties belong in an absolute way to the objects to which they are commonly ascribed gives rise to paradoxes. For if A is larger than B or more numerous than C, it can without change in itself become smaller than B (if B grows) or less numerous than D (if D is a larger group). Needless to say if this is meant as an argument in favour of the view that sense-properties are products of interaction it is a very bad one, for whiteness is not at all the same kind of property as largeness. Perhaps however it is intended not so much as an argument, but more as an apéritif. Get a man to admit that Jones's shortness does not belong absolutely to Jones, but exists only as a relation between Jones and the average man, and you will have him in a more amenable state for persuasion that the stone's whiteness belongs not absolutely to the stone, but is begotten of the intercourse of the stone with the percipient's sense-organs. Commonsense holds, does it, that stones are really grey? But it also holds that Little Tich was really short.¹

Socrates now goes on (156) to reveal what he calls the Mysteries of the Protagorean and Heraclitean thinkers. A philosopher's “Mysteries” must be doctrines which he never published, and so we may infer that what Plato offers us under this title is the theory of perception which he took to underlie views of this kind. It is roughly as follows.

Nothing exists except kinêsis (activity, change, process). There are two kinds of process, the one capable of affecting, the other of being affected—that is of sensing. (This distinction as Socrates says is only relative. B may be an object in one transaction but a subject in another. When I see Jones, Jones is the object, but when Jones sees the tree he is the subject). But processes may be divided not only into subjects and objects, but also into slow and fast. Both subjects and objects—percipients and the things they perceive—are slow processes, but when a subject and an object come together, two quick processes occur. There are, as S...

Table of contents

• Front Cover
• Half Title
• Title Page
• Copyright
• Title Page
• Copyright
• CONTENTS
• PREFACE
• GLOSSARY
• 1. THEORY OF KNOWLEDGE
• 2. COSMOLOGY AND THEORY OF NATURE
• 3. METAPHYSICAL ANALYSIS
• 4. LOGIC AND LANGUAGE
• 5. PLATO'S CONCEPTION OF PHILOSOPHICAL METHOD
• INDEX