Chapter XXVIII · THEÆTETUS.

Subjects and personages in the Theætêtus.

In this dialogue, as in the Parmenides immediately preceding, Plato dwells upon the intellectual operations of mind: introducing the ethical and emotional only in a partial and subordinate way. The main question canvassed is, What is Knowledge — Cognition — Science? After a long debate, turning the question over in many distinct points of view, and examining three or four different answers to the question — all these answers are successively rejected, and the problem remains unsolved.

The two persons who converse with Sokrates are, Theodôrus, an elderly man, eminent as a geometrician, astronomer, &c., and teaching those sciences — and Theætêtus, a young man of great merit and still greater promise: acute, intelligent, and inquisitive — high-principled and courageous in the field, yet gentle and conciliatory to all: lastly, resembling Sokrates in physiognomy and in the flatness of his nose. The dialogue is supposed to have taken place during the last weeks of the life of Sokrates, when his legal appearance as defendant is required to answer the indictment of Melêtus, already entered in the official record.1 The dialogue is here read aloud to Eukleides of Megara and his fellow-citizen Terpsion, by a slave of Eukleides: this last person had recorded it in writing from narrative previously made to him by Sokrates.2 It is prefaced by a short discourse between Eukleides and Terpsion, intended to attract our sympathy and admiration towards the youthful Theætêtus.

Question raised by Sokrates — What is knowledge or Cognition? First answer of Theætêtus, enumerating many different cognitions. Corrected by Sokrates.

In answer to the question put by Sokrates — What is Knowledge or Cognition? Theætêtus at first replies — That there are many and diverse cognitions:— of geometry, of arithmetic, of arts and trades, such as shoemaking, joinery, &c. Sokrates points out (as in the Menon, Hippias Major, and other dialogues) that such an answer involves a misconception of the question: which was general, and required a general answer, setting forth the characteristic common to all cognitions. No one can know what cognition is in shoemaking or any particular case — unless he first knows what is cognition generally.3 Specimens of suitable answers to general questions are then given (or of definition of a general term), in the case of clay — and of numbers square and oblong.4 I have already observed more than once how important an object it was with Plato to impress upon his readers an exact and adequate conception of the meaning of general terms, and the proper way of defining them. For this purpose he brings into contrast the misconceptions likely to arise in the minds of persons not accustomed to dialectic.

Preliminary conversation before the second answer is given. Sokrates describes his own peculiar efficacy — mental obstetric — He cannot teach, but he can evolve knowledge out of pregnant minds.

Theætêtus, before he attempts a second answer, complains how much the subject had embarrassed him. Impressed with what he had heard about the interrogatories of Sokrates, he had tried to solve this problem: but he had not been able to satisfy himself with any attempted solution — nor yet to relinquish the search altogether. “You are in distress, Theætêtus” (observes Sokrates), “because you are not empty, but pregnant.5 You have that within you, of which you need to be relieved; and you cannot be relieved without obstetric aid. It is my peculiar gift from the Gods to afford such aid, and to stimulate the parturition of pregnant minds which cannot of themselves bring forth what is within them.6 I can produce no truth myself: but I can, by my art inherited from my mother the midwife Phænaretê, extract truth from others, and test the answers given by others: so as to determine whether such answers are true and valuable, or false and worthless. I can teach nothing: I only bring out what is already struggling in the minds of youth: and if there be nothing within them, my procedure is unavailing. My most important function is, to test the answers given, how far they are true or false. But most people, not comprehending my drift, complain of me as a most eccentric person, who only makes others sceptical. They reproach me, and that truly enough, with always asking questions, and never saying any thing of my own: because I have nothing to say worth hearing.7 The young companions who frequent my society, often suffer long-continued pains of parturition night and day, before they can be delivered of what is within them. Some, though apparently stupid when they first come to me, make great progress, if my divine coadjutor is favourable to them: others again become tired of me, and go away too soon, so that the little good which I have done them becomes effaced. Occasionally, some of these impatient companions wish to return to me afterwards — but my divine sign forbids me to receive them: where such obstacle does not intervene, they begin again to make progress.”8

Ethical basis of the cross-examination of Sokrates — He is forbidden to pass by falsehood without challenge.

This passage, while it forcibly depicts the peculiar intellectual gift of Sokrates, illustrates at the same time the Platonic manner of describing, full of poetry and metaphor. Cross-examination by Sokrates communicated nothing new, but brought out what lay buried in the mind of the respondent, and tested the value of his answers. It was applicable only to minds endowed and productive: but for them it was indispensable, in order to extract what they were capable of producing, and to test its value when extracted. “Do not think me unkind,” (says Sokrates,) “or my procedure useless, if my scrutiny exposes your answers as fallacious. Many respondents have been violently angry with me for doing so: but I feel myself strictly forbidden either to admit falsehood, or to put aside truth.”9 Here we have a suitable prelude to a dialogue in which four successive answers are sifted and rejected, without reaching, even at last, any satisfactory solution.

Answer of Theætêtus — Cognition is sensible perception: Sokrates says that this is the same doctrine as the Homo Mensura laid down by Protagoras, and that both are in close affinity with the doctrines of Homer, Herakleitus, Empedoklês, &c., all except Parmenides.

The first answer given by Theætêtus is — “Cognition is sensation (or sensible perception)”. Upon this answer Sokrates remarks, that it is the same doctrine, though in other words, as what was laid down by Protagoras — “Man is the measure of all things: of things existent, that they exist: of things non-existent, that they do not exist. As things appear to me, so they are to me: as they appear to you, so they are to you.”10 Sokrates then proceeds to say, that these two opinions are akin to, or identical with, the general view of nature entertained by Herakleitus, Empedoklês, and other philosophers, countenanced moreover by poets like Homer and Epicharmus. The philosophers here noticed (he continues), though differing much in other respects, all held the doctrine that nature consisted in a perpetual motion, change, or flux: that there was no real Ens or permanent substratum, but perpetual genesis or transition.11 These philosophers were opposed to Parmenides, who maintained (as I have already stated in a previous chapter) that there was nothing real except Ens — One, permanent, and unchangeable: that all change was unreal, apparent, illusory, not capable of being certainly known, but only matter of uncertain opinion or estimation.

Plato here blends together three distinct theories for the purpose of confuting them; yet he also professes to urge what can be said in favour of them. Difficulty of following his exposition.

The one main theme intended for examination here (as Sokrates12 expressly declares) is the doctrine — That Cognition is sensible perception. Nevertheless upon all the three opinions, thus represented as cognate or identical,13 Sokrates bestows a lengthened comment (occupying a half of the dialogue) in conversation, principally with Theætêtus, but partly also with Theodôrus. His strictures are not always easy to follow with assurance, because he often passes with little notice from one to the other of the three doctrines which he is examining: because he himself, though really opposed to them, affects in part to take them up and to suggest arguments in their favour: and further because, disclaiming all positive opinion of his own, he sometimes leaves us in doubt what is his real purpose — whether to expound, or to deride, the opinions of others — whether to enlighten Theætêtus, or to test his power of detecting fallacies.14 We cannot always distinguish between the ironical and the serious. Lastly, it is a still greater difficulty, that we have not before us either of the three opinions as set forth by their proper supporters. There remains no work either of Protagoras or of Herakleitus: so that we do not clearly know the subject matter upon which Plato is commenting — nor whether these authors would have admitted as just the view which he takes of their opinions.15

The doctrine of Protagoras is completely distinct from the other doctrines. The identification of them as one and the same is only constructive — the interpretation of Plato himself.

It is not improbable that the three doctrines, here put together by Plato and subjected to a common scrutiny, may have been sometimes held by the same philosophers. Nevertheless, the language16 of Plato himself shows us that Protagoras never expressly affirmed knowledge to be sensible Perception: and that the substantial identity between this doctrine, and the different doctrine maintained by Protagoras, is to be regarded as a construction put upon the two by Plato. That the theories of Herakleitus and Empedokles differed materially from each other, we know certainly: the theory of each, moreover, differed from the doctrine of Protagoras — “Man is the measure of all things”. How this last doctrine was defended by its promulgator, we cannot say. But the defence of it noway required him to maintain — That knowledge is sensible perception. It might be consistently held by one who rejected that definition of knowledge.17 And though Plato tries to refute both, yet the reasonings which he brings against one do not at all tell against the other.

Explanation of the doctrine of Protagoras — Homo Mensura.

The Protagorean doctrine — Man is the measure of all things — is simply the presentation in complete view of a common fact — uncovering an aspect of it which the received phraseology hides. Truth and Falsehood have reference to some believing subject — and the words have no meaning except in that relation. Protagoras brings to view this subjective side of the same complex fact, of which Truth and Falsehood denote the objective side. He refuses to admit the object absolute — the pretended thing in itself — Truth without a believer. His doctrine maintains the indefeasible and necessary involution of the percipient mind in every perception — of the concipient mind in every conception — of the cognizant mind in every cognition. Farther, Protagoras acknowledges many distinct believing or knowing Subjects: and affirms that every object known must be relative to (or in his language, measured by) the knowing Subject: that every cognitum must have its cognoscens, and every cognoscibile its cognitionis capax: that the words have no meaning unless this be supposed: that these two names designate two opposite poles or aspects of the indivisible fact of cognition — actual or potential — not two factors, which are in themselves separate or separable, and which come together to make a compound product. A man cannot in any case get clear of or discard his own mind as a Subject. Self is necessarily omnipresent; concerned in every moment of consciousness, and equally concerned in all, though more distinctly attended to in some than in others.18 The Subject, self, or Ego, is that which all our moments of consciousness have in common and alike: Object is that in which they do or may differ — although some object or other there always must be. The position laid down by Descartes — Cogito, ergo sum — might have been stated with equal truth — Cogito, ergo est (cogitatum aliquid): sum cogitans — est cogitatum — are two opposite aspects of the same indivisible mental fact — cogitatio. In some cases, doubtless, the objective aspect may absorb our attention, eclipsing the subjective: in other cases, the subjective attracts exclusive notice: but in all cases and in every act of consciousness, both are involved as co-existent and correlative. That alone exists, to every man, which stands, or is believed by him to be capable of standing, in some mode of his consciousness as an Object correlative with himself as a Subject. If he believes in its existence, his own believing mind is part and parcel of such fact of belief, not less than the object believed in: if he disbelieves it, his own disbelieving mind is the like. Consciousness in all varieties has for its two poles Subject and Object: there cannot be one of these poles without the opposite pole — north without south — any more than there can be concave without convex (to use a comparison familiar with Aristotle), or front without back: which are not two things originally different and coming into conjunction, but two different aspects of the same indivisible fact.

Perpetual implication of Subject with Object — Relate and Correlate.

In declaring that “Man is the measure of all things” — Protagoras affirms that Subject is the measure of Object, or that every object is relative to a correlative Subject. When a man affirms, believes, or conceives, an object as existing, his own believing or concipient mind is one side of the entire fact. It may be the dark side, and what is called the Object may be the light side, of the entire fact: this is what happens in the case of tangible and resisting substances, where Object, being the light side of the fact, is apt to appear all in all:19 a man thinks of the Something which resists, without attending to the other aspect of the fact of resistance, viz.: his own energy or pressure, to which resistance is made. On the other hand, when we speak of enjoying any pleasure or suffering any pain, the enjoying or suffering Subject appears all in all, distinguished plainly from other Subjects, supposed to be not enjoying or suffering in the same way: yet it is no more than the light side of the fact, of which Object is the dark side. Each particular pain which we suffer has its objective or differential peculiarity, distinguishing it from other sensations, correlating with the same sentient Subject.

Such relativity is no less true in regard to the ratiocinative combinations of each individual, than in regard to his percipient capacities.

The Protagorean dictum will thus be seen, when interpreted correctly, to be quite distinct from that other doctrine with which Plato identifies it: that Cognition is nothing else but sensible Perception. If, rejecting this last doctrine, we hold that cognition includes mental elements distinct from, though co-operating with, sensible perception — the principle of relativity laid down by Protagoras will not be the less true. My intellectual activity — my powers of remembering, imagining, ratiocinating, combining, &c., are a part of my mental nature, no less than my powers of sensible perception: my cognitions and beliefs must all be determined by, or relative to, this mental nature: to the turn and development which all these various powers have taken in my individual case. However multifarious the mental activities may be, each man has his own peculiar allotment and manifestations thereof, to which his cognitions must be relative. Let us grant (with Plato) that the Nous or intelligent Mind apprehends intelligible Entia or Ideas distinct from the world of sense: or let us assume that Kant and Reid in the eighteenth century, and M. Cousin with other French writers in the nineteenth, have destroyed the Lockian philosophy, which took account (they say) of nothing but the à posteriori element of cognition — and have established the existence of other elements of cognition à priori: intuitive beliefs, first principles, primary or inexplicable Concepts of Reason.20 Still we must recollect that all such à priori Concepts, Intuitions, Beliefs, &c., are summed up in the mind: and that thus each man’s mind, with its peculiar endowments, natural or supernatural, is still the measure or limit of his cognitions, acquired and acquirable. The Entia Rationis exist relatively to Ratio, as the Entia Perceptionis exist relatively to Sense. This is a point upon which Plato himself insists, in this very dialogue. You do not, by producing this fact of innate mental intuitions, eliminate the intuent mind; which must be done in order to establish a negative to the Protagorean principle.21 Each intuitive belief whether correct or erroneous — whether held unanimously by every one semper et ubique, or only held by a proportion of mankind — is (or would be, if proved to exist) a fact of our nature; capable of being looked at either on the side of the believing Subject, which is its point of community with all other parts of our nature — or on the side of the Object believed, which is its point of difference or peculiarity. The fact with its two opposite aspects is indivisible. Without Subject, Object vanishes: without Object (some object or other, for this side of the fact is essentially variable), Subject vanishes.

Evidence from Plato proving implication of Subject and Object, in regard to the intelligible world.

That this general doctrine is true, not merely respecting the facts of sense, but also respecting the facts of mental conception, opinion, intellection, cognition — may be seen by the reasoning of Plato himself in other dialogues. How, for example, does Plato prove, in his Timæus, the objective reality of Ideas or Forms? He infers them from the subjective facts of his own mind. The subjective fact called Cognition (he argues) is generically different from the subjective fact called True Opinion: therefore the Object correlating with the One must be distinct from the Object correlating with the other: there must be a Noumenon or νοητόν τι correlating with Nous, distinct from the δοξαστόν τι which correlates with δόξα.22 So again, in the Phædon,23 Sokrates proves the pre-existence of the human soul from the fact that there were pre-existent cognizable Ideas: if there were knowable Objects, there must also have been a Subject Cognoscens or Cognitionis capax. The two are different aspects of one and the same conception: upon which we may doubtless reason abstractedly under one aspect or under the other, though they cannot be separated in fact. Now Both these two inferences of Plato rest on the assumed implication of Subject and Object.24

The Protagorean measure is even more easily shown in reference to the intelligible world than in reference to sense.

In truth, the Protagorean measure or limit is even more plainly applicable to our mental intuitions and mental processes (remembering, imagining, conceiving, comparing, abstracting, combining of hypotheses, transcendental or inductive) than to the matter of our sensible experience.25 In regard to the Entia Rationis, divergence between one theorist and another is quite as remarkable as the divergence between one percipient and another in the most disputable region of Entia Perceptionis. Upon the separate facts of sense, there is a nearer approach to unanimity among mankind, than upon the theories whereby theorising men connect together those facts to their own satisfaction. An opponent of Protagoras would draw his most plausible arguments from the undisputed facts of sense. He would appeal to matter and what are called its primary qualities, as refuting the doctrine. For in describing mental intuitions, Mind or Subject cannot well be overlaid or ignored: but in regard to the external world, or material substance with its primary qualities, the objective side is so lighted up and magnified in the ordinary conception and language — and the subjective side so darkened and put out of sight — that Object appears as if it stood single, apart, and independent.

A man conceives objects, like houses and trees, as existing when he does not actually see or touch them, just as much as when he does see or touch them. He conceives them as existing independent of any actual sensations of his own: and he proceeds to describe them as independent altogether of himself as a Subject — or as absolute, not relative, existences. But this distinction, though just as applied in ordinary usage, becomes inadmissable when brought to contradict the Protagorean doctrine; because the speaker professes to exclude, what cannot be excluded, himself as concipient Subject.26 It is he who conceives absent objects as real and existing, though he neither sees nor touches them: he believes fully, that if he were in a certain position near them, he would experience those appropriate sensations of sight and touch, whereby they are identified. Though he eliminates himself as a percipient, he cannot eliminate himself as a concipient: i.e., as conceiving and believing. He can conceive no object without being himself the Subject conceiving, nor believe in any future contingency without being himself the Subject believing. He may part company with himself as percipient, but he cannot part company with himself altogether. His conception of an absent external object, therefore, when fully and accurately described, does not contradict the Protagorean doctrine. But it is far the most plausible objection which can be brought against that doctrine, and it is an objection deduced from the facts or cognitions of sense.

Object always relative to Subject — Either without the other, impossible. Plato admits this in Sophistes.

I cannot therefore agree with Plato in regarding the Protagorean doctrine — Homo Mensura — as having any dependance upon, or any necessary connection with, the other theory (canvassed in the Theætêtus) which pronounces cognition to be sensible perception. Objects of thought exist in relation to a thinking Subject; as Objects of sight or touch exist in relation to a seeing or touching Subject. And this we shall find Plato himself declaring in the Sophistes (where his Eleatic disputant is introduced as impugning a doctrine substantially the same as that of Plato himself in the Phædon, Timæus, and elsewhere) as well as here in the Theætêtus. In the Sophistes, certain philosophers (called the Friends of Forms or Ideas) are noticed, who admitted that all sensible or perceivable existence (γένεσις — Fientia) was relative to a (capable) sentient or percipient — but denied the relativity of Ideas, and maintained that Ideas, Concepts, Intelligible Entia, were not relative but absolute. The Eleate combats these philosophers, and establishes against them — That the Cogitable or Intelligible existence, Ens Rationis, was just as much relative to an Intelligent or Cogitant subject, as perceivable existence was relative to a Subject capable of perceiving — That Existence, under both varieties, was nothing more than a potentiality, correlating with a counter-potentiality (τὸ γνωστὸν with τὸ γνωστικόν, τὸ αἰσθητὸν with τὸ αἰσθητικόν, and never realised except in implication therewith.27

Plato’s representation of the Protagorean doctrine in intimate conjunction with the Herakleitean.

This doctrine of the Eleate in the Platonic Sophistes coincides with the Protagorean — Homo Mensura — construed in its true meaning: Object is implicated with, limited or measured by, Subject: a doctrine proclaiming the relativeness of all objects perceived, conceived, known, or felt — and the omnipresent involution of the perceiving, conceiving, knowing, or feeling, Subject: the object varying with the Subject. “As things appear to me, so they are to me: as they appear to you, so they are to you.” This theory is just and important, if rightly understood and explained: but whether Protagoras did so explain or understand it, we cannot say; nor does the language of Plato enable us to make out. Plato passes on from this theory to another, which he supposes Protagoras to have held without distinctly stating it: That there is no Ens distinguishable in itself or permanent, or stationary: that all existences are in perpetual flux, motion, change — acting and reacting upon each other, combining with or disjoining from each other.28

Relativity of sensible facts, as described by him.

Turning to the special theory of Protagoras (Homo Mensura), and producing arguments, serious or ironical in its defence, Sokrates says — What you call colour has no definite place or existence either within you or without you. It is the result of the passing collision between your eyes and the flux of things suited to act upon them. It is neither in the agent nor in the patient, but is something special and momentary generated in passing between the two. It will vary with the subject: it is not the same to you, to another man, to a dog or horse, or even to yourself at different times. The object measured or touched cannot be in itself either great, or white, or hot: for if it were, it would not appear different to another Subject. Nor can the Subject touching or measuring be in itself great, or white, or hot: for if so, it would always be so, and would not be differently modified when applied to a different object. Great, white, hot, denote no positive and permanent attribute either in Object or Subject, but a passing result or impression generated between the two, relative to both and variable with either.29

Relations are nothing in the object purely and simply without a comparing subject.

To illustrate this farther (continues Sokrates) — suppose we have here six dice. If I compare them with three other dice placed by the side of them, I shall call the six dice more and double: if I put twelve other dice by the side of them, I shall call the six fewer and half. Or take an old man — and put a growing youth by his side. Two years ago the old man was taller than the youth: now, the youth is grown, so that the old man is the shorter of the two. But the old man, and the six dice, have remained all the time unaltered, and equal to themselves. How then can either of them become either greater or less? or how can either really be so, when they were not so before?30

Relativity twofold — to the comparing Subject — to another object, besides the one directly described.

The illustration here furnished by Sokrates brings out forcibly the negation of the absolute, and the affirmation of universal relativity in all conceptions, judgments, and predications, which he ascribes to Protagoras and Herakleitus. The predication respecting the six dice denotes nothing real, independent, absolute, inhering in them: for they have undergone no change. It is relative, and expresses a mental comparison made by me or some one else. It is therefore relative in two different senses:— 1. To some other object with which the comparison of the dice is made:— 2. To me as comparing Subject, who determine the objects with which the comparison shall be made.31 — Though relativity in both senses is comprehended by the Protagorean affirmation — Homo Mensura — yet relativity in the latter sense is all which that affirmation essentially requires. And this is true of all propositions, comparative or not — whether there be or be not reference to any other object beyond that which is directly denoted. But Plato was here illustrating the larger doctrine which he ascribes to Protagoras in common with Herakleitus: and therefore the more complicated case of relativity might suit his purpose better.

Sokrates now re-states that larger doctrine, in general terms, as follows.

Statement of the doctrine of Herakleitus — yet so as to implicate it with that of Protagoras.

The universe is all flux or motion, divided into two immense concurrent streams of force, one active, the other passive; adapted one to the other, but each including many varieties. One of these is Object: the other is, sentient, cognizant, concipient, Subject. Object as well as Subject is, in itself and separately, indeterminate and unintelligible — a mere chaotic Agent or Patient. It is only by copulation and friction with each other that they generate any definite or intelligible result. Every such copulation, between parts adapted to each other, generates a twin offspring: two correlative and inseparable results infinitely diversified, but always born in appropriate pairs:32 a definite perception or feeling, on the subjective side — a definite thing perceived or felt, on the objective. There cannot be one of these without the other: there can be no objective manifestation without its subjective correlate, nor any subjective without its objective. This is true not merely about the external senses — touch, taste, smell, sight, hearing — but also about the internal, — hot and cold, pleasure and pain, desire, fear, and all the countless variety of our feelings which have no separate names.33 Each of these varieties of feeling has its own object co-existent and correlating with it. Sight, hearing, and smell, move and generate rapidly and from afar; touch and taste, slowly and only from immediate vicinity: but the principle is the same in all. Thus, e.g., when the visual power of the eye comes into reciprocal action with its appropriate objective agent, the result between them is, that the visual power passes out of its abstract and indeterminate state into a concrete and particular act of vision — the seeing a white stone or wood: while the objective force also passes out of its abstract and indeterminate state into concrete — so that it is no longer whiteness, but a piece of white stone or wood actually seen.34

Agent and Patient — No absolute Ens.

Accordingly, nothing can be affirmed to exist separately and by itself. All existences, come only as twin and correlative manifestations of this double agency. In fact neither of these agencies can be conceived independently and apart from the other: each of them is a nullity without the other.35 If either of them be varied, the result also will vary proportionally: each may be in its turn agent or patient, according to the different partners with which it comes into confluence.36 It is therefore improper to say — Such or such a thing exists. Existence absolute, perpetual, and unchangeable is nowhere to be found: and all phrases which imply it are incorrect, though we are driven to use them by habit and for want of knowing better. All that is real is, the perpetual series of changeful and transient conjunctions; each Object, with a certain Subject, — each Subject, with a certain Object.37 This is true not merely of individual objects, but also of those complex aggregates rationally apprehended which receive generic names, man, animal, stone, &c.38 You must not therefore say that any thing is, absolutely and perpetually, good, honourable, hot, white, hard, great — but only that it is so felt or esteemed by certain subjects more or less numerous.39

Arguments derived from dreams, fevers. &c., may be answered.

The arguments advanced against this doctrine from the phenomena of dreams, distempers, or insanity, admit (continues Sokrates) of a satisfactory answer. A man who is dreaming, sick, or mad, believes in realities different from, and inconsistent with, those which he would believe in when healthy. But this is because he is, under those peculiar circumstances, a different Subject, unlike what he was before. One of the two factors of the result being thus changed, the result itself is changed.40 The cardinal principle of Protagoras — the essential correlation, and indefeasible fusion, of Subject and Object, exhibits itself in a perpetual series of definite manifestations. To say that I (the Subject) perceive, — is to say that I perceive some Object: to perceive and perceive nothing, is a contradiction. Again, if an Object be sweet, it must be sweet to some percipient Subject: sweet, but sweet to no one, is impossible.41 Necessity binds the essence of the percipient to that of something perceived: so that every name which you bestow upon either of them implies some reference to the other; and no name can be truly predicated of either, which implies existence (either perpetual or temporary) apart from the other.42

Exposition of the Protagorean doctrine, as given here by Sokrates is to a great degree just. You cannot explain the facts of consciousness by independent Subject and Object.

Such is the exposition which Sokrates is here made to give, of the Protagorean doctrine. How far the arguments, urged by him in its behalf, are such as Protagoras himself either really urged, or would have adopted, we cannot say. In so far as the doctrine asserts essential fusion and implication between Subject and Object, with actual multiplicity of distinct Subjects — denying the reality either of absolute and separate Subject, or of absolute and separate Object43 — I think it true and instructive. We are reminded that when we affirm any thing about an Object, there is always (either expressed or tacitly implied) a Subject or Subjects (one, many, or all), to whom the Object is what it is declared to be. This is the fundamental characteristic of consciousness, feeling, and cognition, in all their actual varieties. All of them are bi-polar or bi-lateral, admitting of being looked at either on the subjective or on the objective side. Comparisons and contrasts, gradually multiplied, between one consciousness and another, lead us to distinguish the one of these points of view from the other. In some cases, the objective view is brought into light and prominence, and the subjective thrown into the dark and put out of sight: in other cases, the converse operation takes place. Sometimes the Ego or Subject is prominent, sometimes the Mecum or Object.44 Sometimes the Objective is as it were divorced from the Subject, and projected outwards, so as to have an illusory appearance of existing apart from and independently of any Subject. In other cases, the subjective view is so exclusively lighted up and conspicuous, that Object disappears, and we talk of a mind conceiving, as if it had no correlative Concept. It is possible, by abstraction, to indicate, to name, and to reason about, the one of these two points of view without including direct notice of the other: this is abstraction or logical separation — a mental process useful and largely applicable, yet often liable to be mistaken for real distinctness and duality. In the present case, the two abstractions become separately so familiar to the mind, that this supposed duality is conceived as the primordial and fundamental fact: the actual, bilateral, consciousness being represented as a temporary derivative state, generated by the copulation of two factors essentially independent of each other. Such a theory, however, while aiming at an impracticable result, amounts only to an inversion of the truth. It aims at explaining our consciousness as a whole; whereas all that we can really accomplish, is to explain, up to a certain point, the conditions of conjunction and sequence between different portions of our consciousness. It also puts the primordial in the place of the derivative, and transfers the derivative to the privilege of the primordial. It attempts to find a generation for what is really primordial — the total series of our manifold acts of consciousness, each of a bilateral character, subjective on one side and objective on the other: and it assigns as the generating factors two concepts obtained by abstraction from these very acts, — resulting from multiplied comparisons, — and ultimately exaggerated into an illusion which treats the logical separation as if it were bisection in fact and reality.

Plato’s attempt to get behind the phenomena. Reference to a double potentiality — Subjective and Objective.

In Plato’s exposition of the Protagorean theory, the true doctrine held by Protagoras,45 and the illusory explanation (whether belonging to him or to Plato himself), are singularly blended together. He denies expressly all separate existence either of Subject or Object — all possibility of conceiving or describing the one as a reality distinct from the other. He thus acknowledges consciousness and cognition as essentially bilateral. Nevertheless he also tries to explain the generation of these acts of consciousness, by the hypothesis of a latens processus behind them and anterior to them — two continuous moving forces, agent and patient, originally distinct, conspiring as joint factors to a succession of compound results. But when we examine the language in which Plato describes these forces, we see that he conceives them only as Abstractions and Potentialities;46 though he ascribes to them a metaphorical copulation and generation. “Every thing is motion (or change): of which there are two sorts, each infinitely manifold: one, having power to act — the other having power to suffer.” Here instead of a number of distinct facts of consciousness, each bilateral — we find ourselves translated by abstraction into a general potentiality of consciousness, also essentially bilateral and multiple. But we ought to recollect, that the Potential is only a concept abstracted from the actual, — and differing from it in this respect, that it includes what has been and what may be, as well as what is. But it is nothing new and distinct by itself: it cannot be produced as a substantive antecedent to the actual, and as if it afforded explanation thereof. The general proposition about motion or change (above cited in the words of Plato), as far as it purports to get behind the fact of consciousness and to assign its cause or antecedent — is illusory. But if considered as a general expression for that fact itself, in the most comprehensive terms — indicating the continuous thread of separate, ever-changing acts of consciousness, each essentially bilateral, or subjective as well as objective — in this point of view the proposition is just and defensible.47

It is to be remembered, that the doctrine here criticised is brought forward by the Platonic Sokrates as a doctrine not his own, but held by others; among whom he ranks Protagoras as one.

Having thus set forth in his own language, and as an advocate, the doctrine of Protagoras, Sokrates proceeds to impugn it: in his usual rambling and desultory way, but with great dramatic charm and vivacity. He directs his attacks alternately against the two doctrines: 1. Homo Mensura: 2. Cognition is sensible perception.

I shall first notice what he advances against Homo Mensura.

Arguments advanced by the Platonic Sokrates against the Protagorean doctrine. He says that it puts the wise and foolish on a par — that it contradicts the common consciousness. Not every one, but the wise man only, is a measure.

It puts every man (he says) on a par as to wisdom and intelligence: and not only every man, but every horse, dog, frog, and other animal along with him. Each man is a measure for himself: all his judgments and beliefs are true: he is therefore as wise as Protagoras and has no need to seek instruction from Protagoras.48 Reflection, study, and dialectic discussion, are superfluous and useless to him: he is a measure to himself on the subject of geometry, and need not therefore consult a professed geometrician like Theodôrus.49

The doctrine is contradicted (continues Sokrates) by the common opinions of mankind: for no man esteems himself a measure on all things. Every one believes that there are some things on which he is wiser than his neighbour — and others on which his neighbour is wiser than he. People are constantly on the look out for teachers and guides.50 If Protagoras advances an opinion which others declare to be false, he must, since he admits their opinion to be true, admit his own opinion to be false.51 No animal, nor any common man, is a measure; but only those men, who have gone through special study and instruction in the matter upon which they pronounce.52

In matters of present sentiment every man can judge for himself. Where future consequences are involved special knowledge is required.

In matters of present and immediate sensation, hot, cold, dry, moist, sweet, bitter, &c., Sokrates acknowledges that every man must judge for himself, and that what each pronounces is true for himself. So too, about honourable or base, just or unjust, holy or unholy — whatever rules any city may lay down, are true for itself: no man, no city, — is wiser upon these matters than any other.53 But in regard to what is good, profitable, advantageous, healthy, &c., the like cannot be conceded. Here (says Sokrates) one man, and one city, is decidedly wiser, and judges more truly, than another. We cannot say that the judgment of each is true;54 or that what every man or every city anticipates to promise good or profit, will necessarily realise such anticipations. In such cases, not merely present sentiment, but future consequences are involved.

Here then we discover the distinction which Plato would draw.55 Where present sentiment alone is involved, as in hot and cold, sweet and bitter, just and unjust, honourable and base, &c., there each is a judge for himself, and one man is no better judge than another. But where future consequences are to be predicted, the ignorant man is incapable: none but the professional Expert, or the prophet,56 is competent to declare the truth. When a dinner is on table, each man among the guests can judge whether it is good: but while it is being prepared, none but the cook can judge whether it will be good.57 This is one Platonic objection against the opinion of Protagoras, when he says that every opinion of every man is true. Another objection is, that opinions of different men are opposite and contradictory,58 some of them contradicting the Protagorean dictum itself.

Plato, when he impugns the doctrine of Protagoras, states that doctrine without the qualification properly belonging to it. All belief relative to the condition of the believing mind.

Such are the objections urged by Sokrates against the Protagorean doctrine — Homo Mensura. There may have been perhaps in the treatise of Protagoras, which unfortunately we do not possess, some reasonings or phrases countenancing the opinions against which Plato here directs his objections. But so far as I can collect, even from the words of Plato himself when he professes to borrow the phraseology of his opponent, I cannot think that Protagoras ever delivered the opinion which Plato here refutes — That every opinion of every man is true. The opinion really delivered by Protagoras appears to have been59 — That every opinion delivered by every man is true, to that man himself. But Plato, when he impugns it, leaves out the final qualification; falling unconsciously into the fallacy of passing (as logicians say) a dicto secundum quid ad dictum simpliciter.60 The qualification thus omitted by Plato forms the characteristic feature of the Protagorean doctrine, and is essential to the phraseology founded upon it. Protagoras would not declare any proposition to be true absolutely, or false absolutely. The phraseology belonging to that doctrine is forced upon him by Plato. Truth Absolute there is none, according to Protagoras. All truth is and must be truth relative to some one or more persons, either actually accepting and believing in it, or conceived as potential believers under certain circumstances. Moreover since these believers are a multitude of individuals, each with his own peculiarities — so no truth can be believed in, except under the peculiar measure of the believing individual mind. What a man adopts as true, and what he rejects as false, are conditioned alike by this limit: a limit not merely different in different individuals, but variable and frequently varying in the same individual. You cannot determine a dog, or a horse, or a child to believe in the Newtonian astronomy: you could not determine the author of the Principia in 1687 to believe what the child Newton had believed in 1647.61 To say that what is true to one man, is false to another — that what was true to an individual as a child or as a youth, becomes false to him in his advanced years, is no real contradiction: though Plato, by omitting the qualifying words, presents it as if it were such. In every man’s mind, the beliefs of the past have been modified or reversed, and the beliefs of the present are liable to be modified or reversed, by subsequent operative causes: by new supervening sensations, emotions, intellectual comparisons, authoritative teaching, or society, and so forth.

All exposition and discussion is an assemblage of individual judgments and affirmations. This fact is disguised by elliptical forms of language.

The fact, that all exposition and discussion is nothing more than an assemblage of individual judgments, depositions, affirmations, negations, &c, is disguised from us by the elliptical form in which it is conducted. For example:— I, who write this book — can give nothing more than my own report, as a witness, of facts known to me, and of what has been said, thought, or done by others, — for all which I cite authorities:— and my own conviction, belief or disbelief, as to the true understanding thereof, and the conclusions deducible. I produce the reasons which justify my opinion: I reply to those reasons which have been supposed by others to justify the opposite. It is for the reader to judge how far my reasons appear satisfactory to his mind.62 To deliver my own convictions, is all that is in my power: and if I spoke with full correctness and amplitude, it would be incumbent on me to avoid pronouncing any opinion to be true or false simply: I ought to say, it is true to me — or false to me. But to repeat this in every other sentence, would be a tiresome egotism. It is understood once for all by the title-page of the book: an opponent will know what he has to deal with, and will treat the opinions accordingly. If any man calls upon me to give him absolute truth, and to lay down the canon of evidence for identifying it — I cannot comply with the request, any farther than to deliver my own best judgment, what is truth — and to declare what is the canon of evidence which guides my own mind. Each reader must determine for himself whether he accepts it or not. I might indeed clothe my own judgments in oracular and vehement language: I might proclaim them as authoritative dicta: I might speak as representing the Platonic Ideal, Typical Man, — or as inspired by a δαίμων like Sokrates: I might denounce opponents as worthless men, deficient in all the sentiments which distinguish men from brutes, and meriting punishment as well as disgrace. If I used all these harsh phrases, I should only imitate what many authors of repute think themselves entitled to say, about THEIR beliefs and convictions. Yet in reality, I should still be proclaiming nothing beyond my own feelings:— the force of emotional association, and antipathy towards opponents, which had grown round these convictions in my own mind. Whether I speak in accordance with others, or in opposition to others, in either case I proclaim my own reports, feelings and judgments — nothing farther. I cannot escape from the Protagorean limit or measures.63

Argument — That the Protagorean doctrine equalises all men and animals. How far true. Not true in the sense requisite to sustain Plato’s objection.

To this theory Plato imputes as a farther consequence, that it equalises all men and all animals. No doubt, the measure or limit as generically described, bears alike upon all: but it does not mark the same degree in all. Each man’s bodily efforts are measured or limited by the amount of his physical force: this is alike true of all men: yet it does not follow that the physical force of all men is equal. The dog, the horse, the new-born child, the lunatic, is each a measure of truth to himself: the philosopher is so also to himself: this is alike true, whatever may be the disparity of intelligence: and is rather more obviously true when the disparity is great, because the lower intelligence has then a very narrow stock of beliefs, and is little modifiable by the higher. But though the Protagorean doctrine declares the dog or the child to be a measure of truth — each to himself — it does not declare either of them to be a measure of truth to me, to you, or to any ordinary by-stander. How far any person is a measure of truth to others, depends upon the estimation in which he is held by others: upon the belief which they entertain respecting his character or competence. Here is a new element let in, of which Plato, in his objection to the Protagorean doctrine, takes no account. When he affirms that Protagoras by his equalising doctrine acknowledged himself to be no better in point of wisdom and judgment than a dog or a child, this inference must be denied.64 The Protagorean doctrine is perfectly consistent with great diversities of knowledge, intellect, emotion, and character, between one man and another. Such diversities are recognised in individual belief and estimation, and are thus comprehended in the doctrine. Nor does Protagoras deny that men are teachable and modifiable. The scholar after being taught will hold beliefs different from those which he held before. Protagoras professed to know more than others, and to teach them: others on their side also believed that he knew more than they, and came to learn it. Such belief on both sides, noway contradicts the general doctrine here under discussion. What the scholar believes to be true, is still true to him: among those things which he believes to be true, one is, that the master knows more than he: in coming to be taught, he acts upon his own conviction. To say that a man is wise, is to say, that he is wise in some one’s estimation: your own or that of some one else. Such estimation is always implied, though often omitted in terms. Plato remarks very truly, that every one believes some others to be on certain matters wiser than himself. In other words, what is called authority — that predisposition to assent, with which we hear the statements and opinions delivered by some other persons — is one of the most operative causes in determining human belief. The circumstances of life are such as to generate this predisposition in every one’s mind to a greater or less degree, and towards some persons more than towards others.

Belief on authority is true to the believer himself — The efficacy of authority resides in the believer’s own mind.

Belief on authority is true to the believer himself, like all his other beliefs, according to the Protagorean doctrine: and in acting upon it, — in following the guidance of A, and not following the guidance of B, — he is still a measure to himself. It is not to be supposed that Protagoras ever admitted all men to be equally wise, though Plato puts such an admission into his mouth as an inference undeniable and obvious. His doctrine affirms something altogether different:— that whether you believe yourself to be wise or unwise, in either case the belief is equally your own — equally the result of your own mental condition and predisposition, — equally true to yourself, — and equally an item among the determining conditions of your actions. That the beliefs and convictions of one person might be modified by another, was a principle held by Protagoras not less than by Sokrates: the former employed as his modifying instrument, eloquent lecturing — the latter, dialectical cross-examination. Both of them recognise the belief of the person to whom they address themselves as true to him, yet at the same time as something which may be modified and corrected, by appealing to what they thought the better parts of it against the worse.

Protagorean formula — is false, to those who dissent from it.

Again — Sokrates imputes it as a contradiction to Protagoras — “Your doctrine is pronounced to be false by many persons: but you admit that the belief of all persons is true: therefore your doctrine is false”.65 Here also Plato omits the qualification annexed by Protagoras to his general principle — Every man’s belief is true — that is, true to him. That a belief should be true, to one man, and false to another — is not only no contradiction to the formula of Protagoras, but is the very state of things which his formula contemplates. He of course could only proclaim it as true to himself. It is the express purpose of his doctrine to disallow the absolutely true and the absolutely false. His own formula, like every other opinion, is false to those who dissent from it: but it is not false absolutely, any more than any other doctrine. Plato therefore does not make out his charge of contradiction.

Plato’s argument — That the wise man alone is a measure — Reply to it.

Some men (says Sokrates) have learnt, — have bestowed study on special matters, — have made themselves wise upon those matters. Others have not done the like, but remain ignorant. It is the wise man only who is a measure: the ignorant man neither is so, nor believes himself to be so, but seeks guidance from the wise.66

Upon this we may remark — First, that even when the untaught men are all put aside, and the erudites or Experts remain alone — still these very erudites or Experts, the men of special study, are perpetually differing among themselves; so that we cannot recognise one as a measure, without repudiating the authority of the rest.67 If by a measure, Plato means an infallible measure, he will not find it in this way: he is as far from the absolute as before. Next, it is perfectly correct that if any man be known to have studied or acquired experience on special matters, his opinion obtains an authority with others (more or fewer), such as the opinion of an ignorant man will not possess. This is a real difference between the graduated man and the non-graduated. But it is a difference not contradicting the theory of Protagoras; who did not affirm that every man’s opinion was equally trustworthy in the estimation of others, but that every man’s opinion was alike a measure to the man himself. The authority of the guide resides in the belief and opinion of those who follow him, or who feel prepared to follow him if necessity arises. A man gone astray on his journey, asks the way to his destination from residents whom he believes to know it, just as he might look at a compass, or at the stars, if no other persons were near. In following their direction, he is acting on his own belief, that he himself is ignorant on the point in question and that they know. He is a measure to himself, both of the extent of his own ignorance, and of the extent of his own knowledge. And in this respect all are alike — every man, woman, child, and animal;68 though they are by no means alike in the estimation of others, as trustworthy authorities.

Plato’s argument as to the distinction between present sensation and anticipation of the future.

A similar remark may be made as to Plato’s distinction between the different matters to which belief may apply: present sensation or sentiment in one case — anticipation of future sensations or sentiments, in another. Upon matters of present sensation and sentiment (he argues), such as hot or cold, sweet or bitter, just or unjust, honourable or base, &c., one man is as good a judge as another: but upon matters involving future contingency, such as what is healthy or unhealthy, — profitable and good, or hurtful and bad, — most men judge badly: only a few persons, possessed of special skill and knowledge, judge well, each in his respective province.

The formula of Relativity does not imply that every man believes himself to be infallible.

I for my part admit this distinction to be real and important. Most other persons admit the same.69 In acting upon it, I follow out my belief, — and so do they. This is a general fact, respecting the circumstances which determine individual belief. Like all other causes of belief, it operates relatively to the individual mind, and thus falls under that general canon of relativity, which it is the express purpose of the Protagorean formula to affirm. Sokrates impugns the formula of relativity, as if it proclaimed every one to believe himself more competent to predict the future than any other person. But no such assumption is implied in it. To say that a man is a measure to himself, is not to say that he is, or, that he believes himself to be, omniscient or infallible. A sick man may mistake the road towards future health, in many different directions. One patient may over-estimate his own knowledge, — that is one way, but only one among several: another may be diffident, and may undervalue his own knowledge: a third may over-estimate the knowledge of his professional adviser, and thus follow an ignorant physician, believing him to be instructed and competent: a fourth, instead of consulting a physician, may consult a prophet, whom Plato70 here reckons among the authoritative infallible measures in respect to future events: a fifth may (like the rhetor Ælius Aristeides71) disregard the advice of physicians, and follow prescriptions enjoined to him in his own dreams, believing them to be sent by Æsculapius the Preserving God. Each of these persons judges differently about the road to future health: but each is alike a measure to himself: the belief of each is relative to his own mental condition and predispositions. You, or I, may believe that one or other of them is mistaken: but here another measure is introduced — your mind or mine.

Plato’s argument is untenable — That if the Protagorean formula be admitted, dialectic discussion would be annulled — The reverse is true — Dialectic recognises the autonomy of the Individual mind.

But the most unfounded among all Plato’s objections to the Protagorean formula, is that in which Sokrates is made to allege, that if it be accepted, the work of dialectical discussion is at an end: that the Sokratic Elenchus, the reciprocal scrutiny of opinions between two dialogists, becomes nugatory — since every man’s opinions are right.72 Instead of right, we must add the requisite qualification, here as elsewhere, by reading, right to the man himself. Now, dealing with Plato’s affirmation thus corrected, we must pronounce not only that it is not true, but that the direct reverse of it is true. Dialectical discussion and the Sokratic procedure, far from implying the negation of the Protagorean formula, involve the unqualified recognition of it. Without such recognition the procedure cannot even begin, much less advance onward to any result. Dialectic operates altogether by question and answer: the questioner takes all his premisses from the answers of the respondent, and cannot proceed in any direction except that in which the respondent leads him. Appeal is always directly made to the affirmative or negative of the individual mind, which is thus installed as measure of truth or falsehood for itself. The peculiar and characteristic excellence of the Sokratic Elenchus consists in thus stimulating the interior mental activity of the individual hearer, in eliciting from him all the positive elements of the debate, and in making him feel a shock when one of his answers contradicts the others. Sokrates not only does not profess to make himself a measure for the respondent, but expressly disclaims doing so: he protests against being considered as a teacher, and avows his own entire ignorance. He undertakes only the obstetric process of evolving from the respondent mind what already exists in it without the means of escape — and of applying interrogatory tests to the answer when produced: if there be nothing in the respondent’s mind, his art is inapplicable. He repudiates all appeal to authority, except that of the respondent himself.73 Accordingly there is neither sense nor fitness in the Sokratic cross-examination, unless you assume that each person, to whom it is addressed, is a measure of truth and falsehood to himself. Implicitly indeed, this is assumed in rhetoric as well as in dialectic: wherever the speaker aims at persuading, he adapts his mode of speech to the predispositions of the hearer’s own mind; and he thus recognises that mind as a measure for itself. But the Sokratic Dialectic embodies the same recognition, and the same essential relativity to the hearer’s mind, more forcibly than any rhetoric. And the Platonic Sokrates (in the Phædrus) makes it one of his objections against orators who addressed multitudes, that they did not discriminate either the specialties of different minds, or the specialties of discourse applicable to each.74

Contrast with the Treatise De Legibus — Plato assumes infallible authority — sets aside Dialectic.

Though Sokrates, and Plato so far forth as follower of Sokrates, employed a colloquial method based on the fundamental assumption of the Protagorean formula — autonomy of each individual mind — whether they accepted the formula in terms, or not; yet we shall find Plato at the end of his career, in his treatise De Legibus, constructing an imaginary city upon the attempted deliberate exclusion of this formula. We shall find him there monopolising all teaching and culture of his citizens from infancy upwards, barring out all freedom of speech or writing by a strict censorship, and severely punishing dissent from the prescribed orthodoxy. But then we shall also find that Plato in that last stage of his life — when he constitutes himself as lawgiver, the measure of truth or falsehood for all his citizens — has at the same time discontinued his early commerce with the Sokratic Dialectics.

Plato in denying the Protagorean formula, constitutes himself the measure for all. Counter-proposition to the formula.

On the whole then, looking at what Plato says about the Protagorean doctrine of Relativity — Homo Mensura — first, his statement what the doctrine really is, next his strictures upon it — we may see that he ascribes to it consequences which it will not fairly carry. He impugns it as if it excluded philosophy and argumentative scrutiny: whereas, on the contrary, it is the only basis upon which philosophy or “reasoned truth” can stand. Whoever denies the Protagorean autonomy of the individual judgment, must propound as his counter theory some heteronomy, such as he (the denier) approves. If I am not allowed to judge of truth and falsehood for myself, who is to judge for me? Plato, in the Treatise De Legibus, answers very unequivocally:— assuming to himself that infallibility which I have already characterised as the prerogative of King Nomos: “I, the lawgiver, am the judge for all my citizens: you must take my word for what is true or false: you shall hear nothing except what my censors approve — and if, nevertheless, any dissenters arise, there are stringent penalties in store for them”. Here is an explicit enunciation of the Counter-Proposition,75 necessary to be maintained by those who deny the Protagorean doctrine. If you pronounce a man unfit to be the measure of truth for himself, you constitute yourself the measure, in his place: either directly as lawgiver — or by nominating censors according to your own judgment. As soon as he is declared a lunatic, some other person must be appointed to manage his property for him. You can only exchange one individual judgment for another. You cannot get out of the region of individual judgments, more or fewer in number: the King, the Pope, the Priest, the Judges or Censors, the author of some book, or the promulgator of such and such doctrine. The infallible measure which you undertake to provide, must be found in some person or persons — if it can be found at all: in some person selected by yourself — that is, in the last result, yourself.76

Import of the Protagorean formula is best seen when we state explicitly the counter-proposition.

It is only when the Counter-Proposition to the Protagorean formula is explicitly brought out, that the full meaning of that formula can be discerned. If you deny it, the basis of all free discussion and scrutiny is withdrawn: philosophy, or what is properly called reasoned truth, disappears. In itself it says little.

Unpopularity of the Protagorean formula — Most believers insist upon making themselves a measure for others, as well as for themselves. Appeal to Abstractions.

Yet little as its positive import may seem to be, it clashes with various illusions, omissions, and exigencies, incident to the ordinary dogmatising process. It substitutes the concrete in place of the abstract — the complete in place of the elliptical. Instead of Truth and Falsehood, which present to us the Abstract and impersonal as if it stood alone — the Objective divested of its Subject — we are translated into the real world of beliefs and disbeliefs, individual believers and disbelievers: matters affirmed or denied by some Subject actual or supposable — by you, by me, by him or them, perhaps by all persons within our knowledge. All men agree in the subjective fact, or in the mental states called belief and disbelief; but all men do not agree in the matters believed and disbelieved, or in what they speak of as Truth and Falsehood. No infallible objective mark, no common measure, no canon of evidence, recognised by all, has yet been found. What is Truth to one man, is not truth, and is often Falsehood, to another: that which governs the mind as infallible authority in one part of the globe, is treated with indifference or contempt elsewhere.77 Each man’s belief, though in part determined by the same causes as the belief of others, is in part also determined by causes peculiar to himself. When a man speaks of Truth, he means what he himself (along with others, or singly, as the case may be) believes to be Truth; unless he expressly superadds the indication of some other persons believing in it. This is the reality of the case, which the Protagorean formula brings into full view; but which most men dislike to recognise, and disguise from themselves as well as from others in the common elliptical forms of speech. In most instances a believer entirely forgets that his own mind is the product of a given time and place, and of a conjunction of circumstances always peculiar, amidst the aggregate of mankind — for the most part narrow. He cannot be content (like Protagoras) to be a measure for himself and for those whom his arguments may satisfy. This would be to proclaim what some German critics denounce as Subjectivism.78 He insists upon constituting himself — or some authority worshipped by himself — or some abstraction interpreted by himself — a measure for all others besides, whether assentient or dissentient. That which he believes, all ought to believe.

This state of mind in reference to belief is usual with most men, not less at the present day than in the time of Plato and Protagoras. It constitutes the natural intolerance prevalent among mankind; which each man (speaking generally), in the case of his own beliefs, commends and exults in, as a virtue. It flows as a natural corollary from the sentiment of belief, though it may be corrected by reflection and social sympathy. Hence the doctrine of Protagoras — equal right of private judgment to each man for himself — becomes inevitably unwelcome.

Aristotle failed in his attempts to refute the Protagorean formula — Every reader of Aristotle will claim the right of examining for himself Aristotle’s canons of truth.

We are told that Demokritus, as well as Plato and Aristotle, wrote against Protagoras. The treatise of Demokritus is lost: but we possess what the two latter said against the Protagorean formula. In my judgment both failed in refuting it. Each of them professed to lay down objective, infallible, criteria of truth and falsehood: Democritus on his side, and the other dogmatical philosophers, professed to do the same, each in his own way — and each in a different way.79 Now the Protagorean formula neither allows nor disallows any one of these proposed objective criteria: but it enunciates the appeal to which all of them must be submitted — the subjective condition of satisfying the judgment of each hearer. Its protest is entered only when that condition is overleaped, and when the dogmatist enacts his canon of belief as imperative, peremptory, binding upon all (allgemeingültig) both assentient and dissentient. I am grateful to Aristotle for his efforts to lay down objective canons in the research of truth; but I claim the right of examining those canons for myself, and of judging whether that, which satisfied Aristotle, satisfies me also. The same right which I claim for myself, I am bound to allow to all others. The general expression of this compromise is, the Protagorean formula. No one demands more emphatically to be a measure for himself, even when all authority is opposed to him, than Sokrates in the Platonic Gorgias.80

Plato’s examination of the other doctrine — That knowledge is Sensible Perception. He adverts to sensible facts which are different with different Percipients.

After thus criticising the formula — Homo Mensura — Plato proceeds to canvass the other doctrine, which he ascribes to Protagoras along with others, and which he puts into the mouth of Theætêtus — “That knowledge is sensible perception”. He connects that doctrine with the above-mentioned formula, by illustrations which exhibit great divergence between one percipient Subject and another. He gives us, as examples of sensible perception, the case of the wind, cold to one man, not cold to another: that of the wine, sweet to a man in health, bitter if he be sickly.81 Perhaps Protagoras may have dwelt upon cases like these, as best calculated to illustrate the relativity of all affirmations: for though the judgments are in reality both equally relative, whether two judges pronounce alike, or whether they pronounce differently, under the same conditions — yet where they judge differently, each stands forth in his own individuality, and the relativity of the judgment is less likely to be disputed.

Such is not the case with all the facts of sense. The conditions of unanimity are best found among select facts of sense — weighing, measuring, &c.

But though some facts of sense are thus equivocal, generating dissension rather than unanimity among different individuals — such is by no means true of the facts of sense taken generally.82 On the contrary, it is only these facts — the world of reality, experience, and particulars — which afford a groundwork and assurance of unanimity in human belief, under all varieties of teaching or locality. Counting, measuring, weighing, are facts of sense simple and fundamental, and comparisons of those facts: capable of being so exhibited that no two persons shall either see them differently or mistrust them. Of two persons exposed to the same wind, one may feel cold, and the other not: but both of them will see the barometer or thermometer alike.83 Πάντα μέτρῳ καὶ ἀριθμῷ καὶ σταθμῷ — would be the perfection of science, if it could be obtained. Plato himself recognises, in more than one place, the irresistible efficacy of weight and measure in producing unanimity; and in forestalling those disputes which are sure to arise where weight and measure cannot be applied.84 It is therefore among select facts of sense, carefully observed and properly compared, that the groundwork of unanimity is to be sought, so far as any rational and universal groundwork for it is attainable. In other words, it is here that we must seek for the basis of knowledge or cognition.

Arguments of Sokrates in examining this question. Divergence between one man and another arises, not merely from different sensual impressibility, but from mental and associative difference.

A loose adumbration of this doctrine is here given by Plato as the doctrine of Protagoras, in the words — Knowledge is sensible perception. To sift this doctrine is announced as his main purpose;85 and we shall see how he performs the task. Sokr. — Shall we admit, that when we perceive things by sight or hearing, we at the same time know them all? When foreigners talk to us in a strange language, are we to say that we do not hear what they say, or that we both hear and know it? When unlettered men look at an inscription, shall we contend that they do not see the writing, or that they both see and know it? Theætêt. — We shall say, under these supposed circumstances, that what we see and hear, we also know. We hear and we know the pitch and intonation of the foreigner’s voice. The unlettered man sees, and also knows, the colour, size, forms, of the letters. But that which the schoolmaster and the interpreter could tell us respecting their meaning, that we neither see, nor hear, nor know. Sokr. — Excellent, Theætêtus. I have nothing to say against your answer.86

This is an important question and answer, which Plato unfortunately does not follow up. It brings to view, though without fully unfolding, the distinction between what is really perceived by sense, and what is inferred from such perception: either through resemblance or through conjunctions of past experience treasured up in memory — or both together. Without having regard to such distinction, no one can discuss satisfactorily the question under debate.87 Plato here abandons, moreover, the subjective variety of impression which he had before noticed as the characteristic of sense:— (the wind which blows cold, and the wine which tastes sweet, to one man, but not to another). Here it is assumed that all men hear the sounds, and see the written letters alike: the divergence between one man and another arises from the different prior condition of percipient minds, differing from each other in associative and reminiscent power.

Argument — That sensible Perception does not include memory — Probability that those who held the doctrine meant to include memory.

Sokrates turns to another argument. If knowledge be the same thing as sensible perception, then it follows, that so soon as a man ceases to see and hear, he also ceases to know. The memory of what he has seen or heard, upon that supposition, is not knowledge. But Theætêtus admits that a man who remembers what he has seen or heard does know it. Accordingly, the answer that knowledge is sensible perception, cannot be maintained.88

Here Sokrates makes out a good case against the answer in its present wording. But we may fairly doubt whether those who affirmed the matter of knowledge to consist in the facts of sense, ever meant to exclude memory. They meant probably the facts of sense both as perceived and as remembered; though the wording cited by Plato does not strictly include so much. Besides, we must recollect, that Plato includes in the meaning of the word Knowledge or Cognition an idea of perfect infallibility: distinguishing it generically from the highest form of opinion. But memory is a fallible process: sometimes quite trustworthy — under other circumstances, not so. Accordingly, memory, in a general sense, cannot be put on a level with present perception, nor said to generate what Plato calls knowledge.

Argument from the analogy of seeing and not seeing at the same time .

The next argument of Plato is as follows. You can see, and not see, the same thing at the same time: for you may close one of your eyes, and look only with the other. But it is impossible to know a thing, and not to know it at the same time. Therefore to know is not the same as to see.89

This argument is proclaimed by Plato as a terrible puzzle, leaving no escape.90 Perhaps he meant to speak ironically. In reality, this puzzle is nothing but a false inference deduced from a false premiss. The inference is false, because if we grant the premiss, that it is possible both to see a thing, and not to see it, at the same time — there is no reason why it should not also be possible to know a thing, and not to know it, at the same time. Moreover, the premiss is also false in the ordinary sense which the words bear: and not merely false, but logically impossible, as a sin against the maxim of contradiction. Plato procures it from a true premiss, by omitting an essential qualification. I see an object with my open eye: I do not see it with my closed eye. From this double proposition, alike intelligible and true, Plato thinks himself authorised to discard the qualification, and to tell me that I see a thing and do not see it — passing à dicto secundum quid ad dictum simpliciter. This is the same liberty which he took with the Protagorean doctrine. Protagoras having said — “Every thing which any man believes is true to that man” — Plato reasons against him as if he had said — “Every thing which any man believes is true”.

Again, argues Plato,91 you cannot say — I know sharply, dimly, near, far, &c. — but you may properly say, I see sharply, dimly, near, far, &c.: another reason to show that knowledge and sensible perception are not the same. After a digression of some length directed against the disciples of Herakleitus — (partly to expose their fundamental doctrine that every thing was in flux and movement, partly to satirise their irrational procedure in evading argumentative debate, and in giving nothing but a tissue of mystical riddles one after another),92 Sokrates returns back to the same debate, and produces more serious arguments, as follows:—

Sokrates maintains that we do not see with our eyes, but that the mind sees through the eyes: that the mind often conceives and judges by itself without the aid of any bodily organ.

Sokr. — If you are asked, With what does a man perceive white and black? you will answer, with his eyes: shrill or grave sounds? with his ears. Does it not seem to you more correct to say, that we see through our eyes rather than with our eyes:— that we hear through our ears, not with our ears. Theætêt. — I think it is more correct. Sokr. — It would be strange if there were in each man many separate reservoirs, each for a distinct class of perceptions.93 All perceptions must surely converge towards one common form or centre, call it soul or by any other name, which perceives through them, as organs or instruments, all perceptible objects. —

We thus perceive objects of sense, according to Plato’s language, with the central form or soul, and through various organs of the body. The various Percepta or Percipienda of tact, vision, hearing — sweet, hot, hard, light — have each its special bodily organ. But no one of these can be perceived through the organ affected to any other. Whatever therefore we conceive or judge respecting any two of them, is not performed through the organ special to either. If we conceive any thing common both to sound and colour, we cannot conceive it either through the auditory or through the visual organ.94

Now there are certain judgments (Sokrates argues) which we make common to both, and not exclusively belonging to either. First, we judge that they are two: that each is one, different from the other, and the same with itself: that each is something, or has existence, and that one is not the other. Here are predicates — existence, non-existence, likeness, unlikeness, unity, plurality, sameness, difference, &c., which we affirm, or deny, not respecting either of these sensations exclusively, but respecting all of them. Through what bodily organ do we derive these judgments respecting what is common to all? There is no special organ: the mind perceives, through itself these common properties.95

Indication of several judgments which the mind makes by itself — It perceives Existence, Difference, &c.

Some matters therefore there are, which the soul or mind apprehends through itself — others, which it perceives through the bodily organs. To the latter class belong the sensible qualities, hardness, softness, heat, sweetness, &c., which it perceives through the bodily organs; and which animals, as well as men, are by nature competent to perceive immediately at birth. To the former class belong existence (substance, essence), sameness, difference, likeness, unlikeness, honourable, base, good, evil, &c., which the mind apprehends through itself alone. But the mind is not competent to apprehend this latter class, as it perceives the former, immediately at birth. Nor does such competence belong to all men and animals; but only to a select fraction of men, who acquire it with difficulty and after a long time through laborious education. The mind arrives at these purely mental apprehensions, only by going over, and comparing with each other, the simple impressions of sense; by looking at their relations with each other; and by computing the future from the present and past.96 Such comparisons and computations are a difficult and gradual attainment; accomplished only by a few, and out of the reach of most men. But without them, no one can apprehend real existence (essence, or substance), or arrive at truth: and without truth, there can be no knowledge.

Sokrates maintains that knowledge is to be found, not in the Sensible Perceptions themselves, but in the comparisons add computations of the mind respecting them.

The result therefore is (concludes Sokrates), That knowledge is not sensible perception: that it is not to be found in the perceptions of sense themselves, which do not apprehend real essence, and therefore not truth — but in the comparisons and computations respecting them, and in the relations between them, made and apprehended by the mind itself.97 Plato declares good and evil, honourable and base, &c., to be among matters most especially relative, perceived by the mind computing past and present in reference to future.98

Examination of this view — Distinction from the views of modern philosophers.

Such is the doctrine which Plato here lays down, respecting the difference between sensible perception, and knowledge or cognition. From his time to the present day, the same topic has continued to be discussed, with different opinions on the part of philosophers. Plato’s views are interesting, as far as his language enables us to make them out. He does not agree with those who treat sensation or sensible perception (in his language, the two are not distinguished) as a bodily phenomenon, and intelligence as a mental phenomenon. He regards both as belonging to the mind or soul. He considers that the mind is sentient as well as intelligent: and moreover, that the sentient mind is the essential basis and preliminary — universal among men and animals, as well as coæval with birth — furnishing all the matter, upon which the intelligent mind has to work. He says nothing, in this dialogue, about the three distinct souls or minds (rational, courageous, and appetitive), in one and the same body, which form so capital a feature in his Timæus and Republic: nothing about eternal, self-existent, substantial Ideas, or about the pre-existence of the soul and its reminiscence as the process of acquiring knowledge. Nor does he countenance the doctrine of innate ideas, instinctive beliefs, immediate mental intuitions, internal senses, &c., which have been recognised by many philosophers. Plato supposes the intelligent mind to work altogether upon the facts of sense; to review and compare them with one another; and to compute facts present or past, with a view to the future. All this is quite different from the mental intuitions and instincts, assumed by various modern philosophers as common to all mankind. The operations, which Plato ascribes to the intelligent mind, are said to be out of the reach of the common man, and not to be attainable except by a few, with difficulty and labour. The distinctive feature of the sentient mind, according to him, is, that it operates through a special bodily organ of sense: whereas the intelligent mind has no such special bodily organ.

Different views given by Plato in other dialogues.

But this distinction, in the first place, is not consistent with Timæus — wherein Plato assigns to each of his three human souls a separate and special region of the bodily organism, as its physical basis. Nor, in the second place, is it consistent with that larger range of observed facts which the farther development of physiology has brought to view. To Plato and Aristotle the nerves and the nervous system were wholly unknown: but it is now ascertained that the optic, auditory, and other nerves of sense, are only branches of a complicated system of sensory and motory nerves, attached to the brain and spinal cord as a centre: each nerve of sense having its own special mode of excitability or manifestation. Now the physical agency whereby sensation is carried on, is, not the organ of sense alone, but the cerebral centre acting along with that organ: whereas in the intellectual and memorial processes, the agency of the cerebral centre and other internal parts of the nervous system are sufficient, without any excitement beginning at the peripheral extremity of the special organ of sense, or even though that organ be disabled. We know the intelligent mind only in an embodied condition: that is, as working along with and through its own physical agency. When Plato, therefore, says that the mind thinks, computes, compares, &c., by itself — this is true only as signifying that it does so without the initiatory stimulus of a special organ of sense; not as signifying that it does so without the central nervous force or currents — an agency essential alike to thought, to sensation, to emotion, and to appetite.

Plato’s discussion of this question here exhibits a remarkable advance in analytical psychology. The mind rises from Sensation, first to Opinion, then to Cognition.

Putting ourselves back to the Platonic period, we must recognise that the discussion of the theory Αἴσθησις = Ἐπιστήμη, as it is conducted by Plato, exhibits a remarkable advance in psychological analysis. In analysing the mental phenomena, Plato displayed much more subtlety and acuteness than his predecessors — as far at least as we have the means of appreciating the latter. It is convenient to distinguish intellect from sensation (or sensible perception) and emotion, though both of them are essential and co-ordinate parts of our mental system, and are so recognised by Plato. It is also true that the discrimination of our sensations from each other, comparisons of likeness or unlikeness between them, observation of co-existence or sequence, and apprehension of other relations between them, &c., are more properly classified as belonging to intellect than to sense. But the language of psychology is, and always has been, so indeterminate, that it is difficult to say how much any writer means to include under the terms Sense99 — Sensation — Sensible Perception — αἴσθησις. The propositions in which our knowledge is embodied, affirm — not sensations detached and isolated, but — various relations of antecedence and consequence, likeness, difference, &c., between two or more sensations or facts of sense. We rise thus to a state of mind more complicated than simple sensation: including (along with sensation), association, memory, discrimination, comparison of sensations, abstraction, and generalisation. This is what Plato calls opinion100 or belief; a mental process, which, though presupposing sensations and based upon them, he affirms to be carried on by the mind through itself, not through any special bodily organ. In this respect it agrees with what he calls knowledge or cognition. Opinion or belief is the lowest form, possessed in different grades by all men, of this exclusively mental process: knowledge or cognition is the highest form of the same, attained only by a select few. Both opinion, and cognition, consist in comparisons and computations made by the mind about the facts of sense. But cognition (in Plato’s view) has special marks:—

1. That it is infallible, while opinion is fallible. You have it101 or you have it not — but there is no mistake possible.

2. That it apprehends what Plato calls the real essence of things, and real truth, which, on the contrary, Opinion does not apprehend.

3. That the person who possesses it can maintain his own consistency under cross-examination, and can test the consistency of others by cross-examining them (λόγον δοῦναι καὶ δέξασθαι).

This at least is the meaning which Plato assigns to the two words corresponding to Cognition and to Opinion, in the present dialogue, and often elsewhere. But he also frequently employs the word Cognition in a lower and more general signification, not restricted, as it is here, to the highest philosophical reach, with infallibility — but comprehending much of what is here treated only as opinion. Thus, for example, he often alludes to the various professional men as possessing Cognition, each in his respective department: the general, the physician, the gymnast, the steersman, the husbandman, &c.102 But he certainly does not mean, that each of them has attained what he calls real essence and philosophical truths — or that any of them are infallible.

Plato did not recognise Verification from experience, or from facts of sense, as either necessary or possible.

One farther remark must be made on Plato’s doctrine. His remark — That Cognition consists not in the affections of sense, but in computation or reasoning respecting those affections, (i. e. abstraction, generalisation, &c.) — is both true and important. But he has not added, nor would he have admitted, that if we are to decide whether our computation is true and right, or false and erroneous — our surest way is to recur to the simple facts of sense. Theory must be verified by observation; wherever that cannot be done, the best guarantee is wanting. The facts themselves are not cognition: yet they are the test by which all computations, pretending to be cognitions, must be tried.103

Second definition given by Theætêtus — That Cognition consists in right or true opinion.

We have thus, in enquiring — What is Knowledge or Cognition? advanced so far as to discover — That it does not consist in sensible perception, but in some variety of that purely mental process which is called opining, believing, judging, conceiving, &c. And here Theætêtus, being called upon for a second definition, answers — That Knowledge consists in right or true opinion. All opinion is not knowledge, because opinion is often false.104

Objection by Sokrates — This definition assumes that there are false opinions. But how can false opinions be possible? How can we conceive Non-Ens: or confound together two distinct realities?.

Sokr. — But you are here assuming that there are false opinions? How is this possible? How can any man judge or opine falsely? What mental condition is it which bears that name? I confess that I cannot tell: though I have often thought of the matter myself, and debated it with others.105 Every thing comes under the head either of what a man knows, or of what he does not know. If he conceives, it must be either the known, or the unknown. He cannot mistake either one known thing for another known thing: or a known thing for an unknown: or an unknown for a known: or one unknown for another unknown. But to form a false opinion, he must err in one or other of these four ways. It is therefore impossible that he can form a false opinion.106

If indeed a man ascribed to any subject a predicate which was non-existent, this would be evidently a false opinion. But how can any one conceive the non-existent? He who conceives must conceive something: just as he who sees or touches, must see or touch something. He cannot see or touch the non-existent: for that would be to see or touch nothing: in other words, not to see or touch at all. In the same manner, to conceive the non-existent, or nothing, is impossible.107 Theæt. — Perhaps he conceives two realities, but confounds them together, mistaking the one for the other. Sokr. — Impossible. If he conceives two distinct realities, he cannot suppose the one to be the other. Suppose him to conceive, just and unjust, a horse and an ox — he can never believe just to be unjust, or the ox to be the horse.108 If, again, he conceives one of the two alone and singly, neither could he on that hypothesis suppose it to be the other: for that would imply that he conceived the other also.

Waxen memorial tablet in the mind, on which past impressions are engraved. False opinion consists in wrongly identifying present sensations with past impressions.

Let us look again in another direction (continues Sokrates). We have been hasty in our concessions. Is it really impossible for a man to conceive, that a thing, which he knows, is another thing which he does not know? Let us see. Grant me the hypothesis (for the sake of illustration), that each man has in his mind a waxen tablet — the wax of one tablet being larger, firmer, cleaner, and better in every way, than that of another: the gift of Mnemosynê, for inscribing and registering our sensible perceptions and thoughts. Every man remembers and knows these, so long as the impressions of them remain upon his tablet: as soon as they are blotted out, he has forgotten them and no longer knows them.109 Now false opinion may occur thus. A man having inscribed on his memorial tablet the impressions of two objects A and B, which he has seen before, may come to see one of these objects again; but he may by mistake identify the present sensation with the wrong past impression, or with that past impression to which it does not belong. Thus on seeing A, he may erroneously identify it with the past impression B, instead of A: or vice versâ.110 False opinion will thus lie, not in the conjunction or identification of sensations with sensations — nor of thoughts (or past impressions) with thoughts — but in that of present sensations with past impressions or thoughts.111

Sokrates refutes this assumption. Dilemma. Either false opinion is impossible, or else a man may know what he does not know.

Having laid this down, however, Sokrates immediately proceeds to refute it. In point of fact, false conceptions are found to prevail, not only in the wrong identification of present sensations with past impressions or thoughts, but also in the wrong identification of one past impression or thought with another. Thus a man, who has clearly engraved on his memorial tablet the conceptions of five, seven, eleven, twelve, — may nevertheless, when asked what is the sum of seven and five, commit error and answer eleven: thus mistaking eleven for twelve.

We are thus placed in this dilemma — Either false opinion is an impossibility:— Or else, it is possible that what a man knows, he may not know. Which of the two do you choose?112

He draws distinction between possessing knowledge, and having it actually in hand. Simile of the pigeon-cage with caught pigeons turned into it and flying about.

To this question no answer is given. But Sokrates, — after remarking on the confused and unphilosophical manner in which the debate has been conducted, both he and Theætêtus having perpetually employed the words know, knowledge, and their equivalents, as if the meaning of the words were ascertained, whereas the very problem debated is, to ascertain their meaning113 — takes up another path of enquiry. He distinguishes between possessing knowledge, — and having it actually in hand or on his person: which distinction he illustrates by comparing the mind to a pigeon-cage. A man hunts and catches pigeons, then turns them into the cage, within the limits of which they fly about: when he wants to catch any one of them for use, he has to go through a second hunt, sometimes very troublesome: in which he may perhaps either fail altogether, or catch the wrong one instead of the right. The first hunt Sokrates compares to the acquisition of knowledge: the second, to the getting it into his hand for use.114 A man may know, in the first sense, and not know, in the second: he may have to hunt about for the cognition which (in the first sense) he actually possesses. In trying to catch one cognition, he may confound it with another: and this constitutes false opinion — the confusion of two cognita one with another.115