10 Plato, Theætêt. pp. 151 E — 152 A.
Theætêt. οὐκ ἄλλο τί ἐστιν ἐπιστήμη ἢ αἴσθησις.…
Sokrat. Κινδυνεύεις μέντοι λόγον οὐ φαῦλον εἰρηκέναι περὶ ἐπιστήμης, ἀλλ’ ὅν ἔλεγε καὶ Πρωταγόρας· τρόπον δέ τινα ἄλλον εἴρηκε τὰ αὐτὰ ταῦτα. Φησὶ γάρ που — Πάντων χρημάτων μέτρον ἄνθρωπον εἶναι, τῶν μὲν ὄντων, ὡς ἔστι — τῶν δὲ μὴ ὄντων, ὡς οὐκ ἔστιν. Ἀνέγνωκας γάρ που;
Theætêt. Ἀνέγνωκα καὶ πολλάκις.
Sokrat. Οὐκοῦν οὕτω πως λέγει, ὠς οἷα μὲν ἕκαστα ἐμοὶ φαίνεται, τοιαῦτα μέν ἐστιν ἐμοὶ — οἷα δὲ σοί, τοιαῦτα δὲ αὖ σοί· ἀνθρωπος δὲ σύ τε κἀγώ.
Theætêt. Λέγει γὰρ οὖν οὕτως.
Here Plato appears to transcribe the words of Protagoras (compare p. 161 B, and the Kratylus, p. 386 A) which distinctly affirm the doctrine of Homo Mensura — Man is the measure of all things, — but do not affirm the doctrine, that knowledge is sensible perception. The identification between the two doctrines is asserted by Plato himself. It is Plato who asserts “that Protagoras affirmed the same doctrine in another manner,” citing afterwards the manner in which he supposed Protagoras to affirm it. If there had been in the treatise of Protagoras any more express or peremptory affirmation of the doctrine “that knowledge is sensible perception,” Plato would probably have given it here.
11 Plato, Theætêt. p. 152 E. καὶ περὶ τούτου πάντες ἑξῆς οἱ σοφοὶ πλὴν Παρμενίδου ξυμφερέσθων, Πρωταγόρας τε καὶ Ἡράκλειτος καὶ Ἐμπεδοκλῆς, καὶ τῶν ποιητῶν οἱ ἄκροι τῆς ποιήσεως ἑκατέρας, κωμῳδίας μὲν Ἐπίχαρμος, τραγῳδίας δὲ Ὅμηρος.
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
12 Plato, Theætêt. p. 163 A.
13 Plato, Theætêt. p. 160 D. Sokrat. Παγκάλως ἄρα σοι εἴρηται ὅτι ἐπιστήμη οὐκ ἄλλο τί ἐστιν ἢ αἴσθησις· καὶ εἰς ταὐτὸν συμπέπτωκε, κατὰ μὲν Ὅμηρον καὶ Ἡράκλειτον καὶ πᾶν τὸ τοιοῦτον φῦλον, οἷον ῥεύματα κινεῖσθαι τὰ πάντα — κατὰ δὲ Πρωταγόραν τὸν σοφώτατον, πάντων χρημάτων ἄνθρωπον μέτρον εἶναι — κατὰ δὲ Θεαίτητον, τούτων οὗτως ἐχόντων, αἴσθησιν ἐπιστήμην γίγνεσθαι.
14 See the answer of Theætêtus and the words of Sokrates following, p. 157 C.
15 It would be hardly necessary to remark, that when Plato professes to put a pleading into the mouth of Protagoras (pp. 165-166) we have no other real speaker than Plato himself, if commentators did not often forget this. Steinhart indeed tells us (Einleit. zum Theætêt. pp. 36-47) positively — that Plato in this pleading keeps in the most accurate manner (auf das genaueste) to the thoughts of Protagoras, perhaps even to his words. How Steinhart can know this I am at a loss to understand. To me it seems very improbable. The mere circumstance that Plato forces into partnership three distinct theories, makes it probable that he did not adhere to the thoughts or language of any one of them.
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.
16 See Theætêt. p. 152 A. This is admitted (to be a construction put by Plato himself) by Steinhart in his note 7, p. 214, Einleitung zum Theætêtus, though he says that Plato’s construction is the right one.
17 Dr. Routh, in a note upon his edition of the Euthydêmus of Plato (p. 286 C) observes:— “Protagoras docebat, Πάντων χρημάτων μέτρον ἄνθρωπον εἶναι, τῶν μὲν ὄντων, ὡς ἔστι· τῶν δὲ μὴ ὄντων, ὡς οὐκ ἔστι. Quâ quidem opinione qualitatum sensilium sine animi perceptione existentiam sustulisse videtur.”
The definition here given by Routh is correct as far as it goes, though too narrow. But it is sufficient to exhibit the Protagorean doctrine as quite distinct from the other doctrine, ὅτι ἐπιστήμη οὐκ ἄλλο τί ἐστιν ἢ αἴσθησις.
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.
18 In regard to the impossibility of carrying abstraction so far as to discard the thinking subject, see Hobbes, Computation or Logic, ch. vii. 1.
“In the teaching of natural philosophy I cannot begin better than from privation; that is, from feigning the world to be annihilated. But if such annihilation of all things be supposed, it may perhaps be asked what would remain for any man (whom only I except from this universal annihilation of things) to consider as the subject of philosophy, or at all to reason upon; or what to give names unto for ratiocination’s sake.
“I say, therefore, there would remain to that man ideas of the world, and of all such bodies as he had, before their annihilation, seen with his eyes, or perceived by any other sense; that is to say, the memory and imagination of magnitudes, motions, sounds, colours, &c., as also of their order and parts. All which things, though they be nothing but ideas and phantasms, happening internally to him that imagineth, yet they will appear as if they were external and not at all depending upon any power of the mind. And these are the things to which he would give names and subtract them from, and compound them with one another. For seeing that after the destruction of all other things I suppose man still remaining, and namely that he thinks, imagines, and remembers, there can be nothing for him to think of but what is past.… Now things may be considered, that is, be brought into account, either as internal accidents of our mind, in which manner we consider them when the question is about some faculty of the mind: or, as species of external things, not as really existing, but appearing only to exist, or to have a being without us. And in this manner we are now to consider them.”
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.
19 “Nobiscum semper est ipsa quam quærimus (anima); adest, tractat, loquitur — et, si fas est dicere, inter ista nescitur.” (Cassiodorus, De Animâ, c. 1, p. 594, in the edition of his Opera Omnia, Venet. 1729).
“In the primitive dualism of consciousness, the Subject and Object being inseparable, either of them apart from the other must be an unknown quantity: the separation of either must be the annihilation of both.” (F. W. Farrar, Chapters on Language, c. 23, p. 292: which chapter contains more on the same topic, well deserving of perusal.)
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.
20 See M. Jouffroy, Préface à sa Traduction des Œuvres de Reid, pp. xcvii.-ccxiv.
M. Jouffroy, following in the steps of Kant, declares these à priori beliefs or intuitions to be altogether relative to the human mind. “Kant, considérant que les conceptions de la raison sont des croyances aveugles auxquelles notre esprit se sent fatalement déterminé par sa nature, en conclut qu’elles sont rélatives à cette nature: que si notre nature était autre, elles pourraient être différentes: que par conséquent, elles n’ont aucune valeur absolue: et qu’ainsi notre vérité, notre science, notre certitude, sont une vérité, une science, une certitude, purement subjective, purement humaine — à laquelle nous sommes déterminés à nous fier par notre nature, mais qui ne supporte pas l’examen et n’a aucune valeur objective” (p. clxvii.) … “C’est ce que répéte Kant quand il soutient que l’on ne peut objectiver le subjectif: c’est à dire, faire que la vérité humaine cesse d’être humaine, puisque la raison qui la trouve est humaine. On peut exprimer de vingt manières différentes cette impossibilité: elle reste toujours la même, et demeure toujours insurmontable,” p. cxc. Compare p. xcvii. of the same Preface.
M. Pascal Galuppi (in his Lettres Philosophiques sur les Vicissitudes de la Philosophie, translated from the Italian by M. Peisse, Paris, 1844) though not agreeing in this variety of à priori philosophy, agrees with Kant in declaring the à priori element of cognition to be purely subjective, and the objective element to be à posteriori (Lett. xiv. pp. 337-338), or the facts of sense and experience. “L’ordre à priori, que Kant appelle transcendental, est purement idéal, et dépourvu de toute réalité. Je vis, qu’en fondant la connaissance sur l’ordre à priori, on arrive nécessairement au scepticisme: et je reconnus que la doctrine Écossaise est la mère légitime du Criticisme Kantien, et par conséquent, du scepticisme, qui est la conséquence de la philosophie critique. Je considérai comme de haute importance ce problème de Kant. Il convient de déterminer ce qu’il y a d’objectif, et ce qu’il y a de subjectif, dans la connaissance. Les Empiriques n’admettent dans la connaissance d’autres élémens que les objectifs,” &c.
21 See this point handled in Sextus Empiric. adv. Mathemat. viii. 355-362. We may here cite a remark of Simplikius in his Commentary on the Categories of Aristotle (p. 64, a. in Schol. Brandis). Aristotle (De Animâ, iii. 2, 426, a. 19; Categor. p. 7, b. 23) lays down the doctrine that in most cases Relata or (τὰ πρός τι) are “simul Naturâ, καὶ συναναιρεῖ ἄλληλα”: but that in some Relata this is not true: for example, τὸ ἐπιστητὸν is relative to ἐπιστήμη, yet still it would seem prior to ἐπιστήμη (πρότερον ἂν δόξειε τῆς ἐπιστήμης εἶναι). There cannot be ἐπιστήμη without some ἐπιστητόν: but there may be ἐπιστητὸν without any ἐπιστήμη. There are few things, if any (he says), in which the ἐπιστητὸν (cognoscibile) is simul naturâ with ἐπιστήμη (or cognitio) and cannot be without it.
Upon which Simplikius remarks, What are these few things? Τίνα δὲ τὰ ὀλίγα ἐστίν, ἐφ’ ὧν ἅμα τῷ ἐπιστητῷ ἡ ἐπιστήμη ἐστίν; Τὰ ἄνευ ὕλης, τὰ νοητά, ἅμα τῷ κατ’ ἐνεργείαν ἀεὶ ἐστώσῃ ἐπιστήμη ἔστιν, εἴτε καὶ ἐν ἡμῖν ἐστί τις τοιαύτη ἀεὶ ἄνω μένουσα, … εἴτε καὶ ἐν τῷ κατ’ ἐνεργείαν vῷ εἴ τις καὶ τὴν νόησιν ἐκείνην ἐπιστήμην ἕλοιτο καλεῖν. δύναται δὲ καὶ διὰ τὴν τῶν κοινῶν ὑπόστασιν εἰρῆσθαι, τὴν ἐξ ἀφαιρέσεως· ἅμα γὰρ τῇ ὑποστάσει τούτων καὶ ἡ ἐπιστήμη ἐστίν. ἀληθὲς δὲ καὶ ἐπὶ τῶν ἀναπλασμάτων τῶν τε ἐν τῇ φαντασίᾳ καὶ τῶν τεχνιτῶν· ἅμα γὰρ χίμαιρα καὶ ἡ ἐπιστήμη χιμαίρας.
We see from hence that Simplikius recognises Concepts, Abstractions, and Fictions, to be dependent on the Conceiving, Abstracting, Imagining, Mind — as distinguished from objects of Sense, which he does not recognise as dependent in the like manner. He agrees in the doctrine of Protagoras as to the former, but not as to the latter. This illustrates what I have affirmed, That the Protagorean doctrine of “Homo Mensura” is not only unconnected with the other principle (that Knowledge is resolvable into sensible perception) to which Aristotle and Plato would trace it — but that there is rather a repugnance between the two. The difficulty of proving the doctrine, and the reluctance to admit it, is greatest in the case of material objects, least in the case of Abstractions, and General Ideas. Yet Aristotle, in reasoning against the Protagorean doctrine (Metaphysic. Γ. pp. 1009-1010, &c.) treats it like Plato, as a sort of corollary from the theory that Cognition is Sensible Perception.
Simplikius farther observes (p. 65, b. 14) that Aristotle is not accurate in making ἐπιστητὸν correlate with ἐπιστήμη: that in Relata, the potential correlates with the potential, and the actual with the actual. The Cognoscible is correlative, not with actual cognition (ἐπιστήμη) but with potential Cognition, or with a potential Cognoscens. Aristotle therefore is right in saying that there may be ἐπιστητὸν without ἐπιστήμη, but this does not prove what he wishes to establish.
Themistius, in another passage of the Aristotelian Scholia, reasoning against Boethus, observes to the same effect as Simplikius, that in relatives, the actual correlates with the actual, and the potential with the potential:—
Καίτοι, φησί γε ὁ Βοηθός, οὐδὲν κωλύει τὸν ἀριθμὸν εἶναι καὶ δίχα τοῦ ἀριθμοῦντος, ὥσπερ οἶμαι τὸ αἰσθητὸν καὶ δίχα τοῦ αἰσθανομένου· σφάλλεται δέ, ἅμα γὰρ τὰ πρὸς τί, καὶ τὰ δυνάμει πρὸς τὰ δυνάμει· ὥστε εἰ μὴ καὶ ἀριθμητικόν, οὐδὲ τὸ ἀριθμητόν (Schol. ad Aristot. Physic. iv. p. 223, a. p. 393, Schol. Brandis).
Compare Aristotel. Metaphysic. M. 1087, a. 15, about τὸ ἐπίστασθαι δυνάμει and τὸ ἐπίστασθαι ἐνεργείᾳ.
About the essential co-existence of relatives — Sublato uno, tollitur alterum — see also Sextus Empiric. adv. Mathematicos, vii. 395, p. 449, Fabric.
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
22 Plato, Timæus, p. 51 B-E, compare Republic, v. p. 477.
See this reasoning of Plato set forth in Zeller, Die Phil. der Griech. vol. ii. pp. 412-416, ed. 2nd.
Nous, according to Plato (Tim. 51 E), belongs only to the Gods and to a select few among mankind. It is therefore only to the Gods and to these few men that Νοητὰ exist. To the rest of mankind Νοητὰ are non-apparent and non-existent.
23 Plato, Phædon, pp. 76-77. ἴση ἀνάγκη ταῦτά τε (Ideas or Forms) εἶναι, καὶ τὰς ἡμετέρας ψυχὰς πρὶν καὶ ἡμᾶς γεγονέναι — καὶ εἰ μὴ ταῦτα, οὐδὲ τάδε. Ὑπερφυῶς, ἔφη ὁ Σιμμίας, δοκεῖ μοι ἡ αὐτὴ ἀνάγκη εἶναι, καὶ εἰς καλόν γε καταφεύγει ὁ λόγος εἰς τὸ ὁμοίως εἶναι τήν τε ψυχὴν ἡμῶν πρὶν γενέσθαι ἡμᾶς καὶ τὴν οὐσίαν ἣν σὺ νῦν λέγεις.
Compare p. 92 E of the same dialogue with the notes of Wyttenbach and Heindorf — “Haec autem οὐσία Idearum, rerum intelligibilium, αὐτῆς ἐστὶν (sc. τῆς ψυχῆς) ut hoc loco dicitur, est propria et possessio animæ nostræ,” &c.
About the essential implication of Νοῦς with the Νοητά, as well as of τὸ δόξαζον with τὰ δοξαζόμενα, and of τὸ αἰσθανόμενον with τὰ αἰσθητά, see Plutarch, De Animæ Procreat. in Timæo, pp. 1012-1024; and a curious passage from Joannes Philoponus ad Aristot. Physica, cited by Karsten in his Commentatio De Empedoclis Philosophiâ, p. 372, and Olympiodorus ad Platon. Phædon, p. 21. τὸν νοῦν φαμὲν ἀκριβῶς γινώσκειν, διότι αὐτός ἐστι τὸ νοητόν.
Sydenham observes, in a note upon his translation of the Philêbus (note 76, p. 118), “Being Intelligent and Being Intelligible are not only correlatives, but are so in their very essence: neither of them can be at all, without the Being of the other”.
24 I think that the inference in the Phædon is not necessary to prove that conclusion, nor in itself just. For when I speak of Augustus and Antony as having once lived, and as having fought the battle of Actium, it is noway necessary that I should believe myself to have been then alive and to have seen them: nor when I speak of civil war as being now carried on in the United States of America, is it necessary that I should believe myself to be or to have been on the spot as a percipient witness. I believe, on evidence which appears to me satisfactory, that both these are real facts: that is, if I had been at Actium on the day of the battle, or if I were now in the United States, I should see and witness the facts here affirmed. These latter words describe the subjective side of the fact, without introducing any supposition that I have been myself present and percipient.
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.
25 Bacon remarks that the processes called mental or intellectual are quite as much relative to man as those called sensational or perceptive. “Idola Tribûs sunt fundata in ipsâ naturâ humanâ. Falso enim asseritur, Sensum humanum esse mensuram rerum: quin contra, omnes perceptiones, tam Sensûs quam Mentis, sunt ex analogiâ hominis, non ex analogiâ Universi.”
Nemesius, the Christian Platonist, has a remark bearing upon this question. He says that the lower animals have their intellectual movements all determined by Nature, which acts alike in all the individuals of the species, but that the human intellect is not wholly determined by Nature; it has a freer range, larger stores of ideas, and more varied combinations: hence its manifestations are not the same in all, but different in different individuals — ἐλεύθερον γάρ τι καὶ αὐτεξούσιον τὸ λογικόν, ὅθεν οὐχ ἓν καὶ ταὐτὸν πᾶσιν ἔργον ἀνθρώποις, ὡς ἑκάστῳ εἴδει τῶν ἀλόγων ζώων· φύσει γὰρ μόνῃ τὰ τοιαῦτα κινεῖται, τὰ δὲ φύσει ὁμοίως παρὰ πᾶσίν ἐστιν· αἱ δὲ λογικαὶ πράξεις ἄλλαι παρ’ ἄλλοις καὶ οὐκ ἐξ ἀνάγκης αἱ αὗται παρὰ πᾶσιν (De Nat. Hom., c. ii. p. 53. ed. 1565).
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.
26 Bishop Berkeley observes:—
“But, say you, surely there is nothing easier than to imagine trees, for instance, in a park, or books existing in a closet, and nobody by to perceive them. I answer, you may so — there is no difficulty in it. But what is all this, more than framing in your mind certain ideas which you call books and trees, and at the same time omitting to frame the idea of any one that may perceive them? But do not you yourself perceive or think of them all the while? This therefore is nothing to the purpose. It only shows you have the power of imagining or forming ideas in your mind: but it doth not show that you can conceive it possible the objects of your thought may exist without the mind. To make out this, it is necessary that you conceive them existing unconceived or unthought of, which is a manifest repugnancy. When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas. But the mind, taking no notice of itself, is deluded to think it can and doth conceive bodies existing unthought of or without the mind, though at the same time they are apprehended by or exist in itself.”
Berkeley, Principles of Human Knowledge, sect. xxiii. p. 34, ed. of Berkeley’s Works, 1820. The same argument is enforced in Berkeley’s First Dialogue between Hylas and Philonous, pp. 145-146 of the same volume.
I subjoin a passage from the work of Professor Bain on Psychology, where this difficult subject is carefully analysed (The Senses and the Intellect, p. 370). “There is no possible knowledge of the world except in reference to our minds. Knowledge means a state of mind: the knowledge of material things is a mental thing. We are incapable of discussing the existence of an independent material world: the very act is a contradiction. We can speak only of a world presented to our own minds. By an illusion of language we fancy that we are capable of contemplating a world which does not enter into our own mental existence: but the attempt belies itself, for this contemplation is an effort of mind.”
“Solidity, extension, space — the foundation properties of the material world — mean, as has been said above, certain movements and energies of our own bodies, and exist in our minds in the shape of feelings of force, allied with visible and tactile, and other sensible impressions. The sense of the external is the consciousness of particular energies and activities of our own.”
(P. 376). “We seem to have no better way of assuring ourselves and all mankind, that with the conscious movement of opening the eyes there will always be a consciousness of light, than by saying that the light exists as an independent fact, without any eyes to see it. But if we consider the fact fairly we shall see that this assertion errs, not simply in being beyond any evidence that we can have, but also in being a self-contradiction. We are affirming that to have an existence out of our minds, which we cannot know but as in our minds. In words we assert independent existence, while in the very act of doing so we contradict ourselves. Even a possible world implies a possible mind to conceive it, just as much as an actual world implies an actual mind. The mistake of the common modes of expression on this matter is the mistake of supposing the abstractions of the mind to have a separate and independent existence. Instead of looking upon the doctrine of an external and independent world as a generalisation or abstraction grounded on our particular experiences, summing up the past and predicting the future, we have got into the way of maintaining the abstraction to be an independent reality, the foundation, or cause, or origin, of all these experiences.”
To the same purpose Mr. Mansel remarks in his Bampton Lectures on “The Limits of Religious Thought,” page 52:
“A second characteristic of Consciousness is, that it is only possible in the form of a relation. There must be a Subject or person conscious, and an Object or thing of which he is conscious. There can be no consciousness without the union of these two factors; and in that union each exists only as it is related to the other. The subject is a subject only in so far as it is conscious of an object: the object is an object only in so far as it is apprehended by a subject: and the destruction of either is the destruction of consciousness itself. It is thus manifest that a consciousness of the Absolute is equally self-contradictory with that of the Infinite.… Our whole notion of Existence is necessarily relative, for it is existence as conceived by us. But Existence, as we conceive it, is but a name for the several ways in which objects are presented to our consciousness — a general term embracing a variety of relations.… To assume Absolute Existence as an object of thought is thus to suppose a relation existing when the related terms exist no longer. An object of thought exists, as such, in and through its relation to a thinker; while the Absolute, as such, is independent of all relation.”
Dr. Henry More has also a passage asserting the essential correlation on which I am here insisting (Immortality of the Soul, ch. ii. p. 3). And Professor Ferrier, in his Institutes of Metaphysic, has given much valuable elucidation respecting the essential relativity of cognition.
Though this note is already long, I shall venture to add from an eminent German critic — Trendelenburg — a passage which goes to the same point.
“Das Sein ist als die absolute Position erklärt worden. Der Begriff des Seins drücke blos das aus: es werde bei dem einfachen Setzen eines Was sein Bewenden haben. Es hat sich hier die abstracte Vorstellung des Seins nur in eine verwandte Anschauung umgekleidet; denn das Gesetzte steht in dem Raum da; und insofern fordert die absolute Position schon den Begriff des seiendem Etwas, das gesetzt wird. Fragt man weiter, so ist in der absoluten Position schon derjenige mitgedacht, der da setzt. Das Sein wird also nicht unabhängig aus sich selbst bestimmt, sondern zur Erklärung ein Verhältniss zu der Thätigkeit des Gedankens herbeigezogen.
“Aehnlich würde jede von vorn herein versuchte Bestimmung des Denkens ausfallen. Man würde es nur durch einen Bezug zu den Dingen erläutern können, welche in dem Denken Grund und Mass finden. Wir begeben uns daher jeder Erklärung, und setzen eine Vorstellung des Denkens und Seins voraus, in der Hoffnung dass beide mit jedem Schritt der Untersuchung sich in sich selbst bestimmen werden.” “Indem wir Denken und Sein unterscheiden, fragen wir, wie ist es möglich, dass sich im Erkennen Denken und Sein vereinigt? Diese Vereinigung sprechen wir vorläufig als eine Thatsache aus, die das Theoretische wie das Praktische beherrscht.” Trendelenburg, Logische Untersuchungen, sect. 3, pp. 103-104, Berlin, 1840.
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