Note 99 — Chapter XXVIII · THEÆTETUS.

The discussion in pp. 184-186-186 of the Theætêtus is interesting as the earliest attempt remaining to classify psychological phenomena. What Demokritus and others proposed with the same view — the analogy or discrepancy between τὸ αἰσθάνεσθαι and τὸ νοεῖν — we gather only from the brief notices of Aristotle and others. Plato considers himself to have established, that “cognition is not to be sought at all in sensible perception, but in that function, whatever it be, which is predicated of the mind when it busies itself per se (i.e. not through any special bodily organ) about existences” (p. 187 A). We may here remark, as to the dispute between Plato and Protagoras, that Plato here does not at all escape from the region of the Relative, or from the Protagorean formula, Homo Mensura. He passes from Mind Percipient to Mind Cogitant; but these new Entia cogitationis (as his language implies) are still relative, though relative to the Cogitant and not to the Percipient. He reduces Mind Sentient to the narrowest functions, including only each isolated impression of one or other among the five senses. When we see a clock on the wall and hear it strike twelve — we have a visual impression of black from the hands, of white from the face, and an audible impression from each stroke. But this is all (according to Plato) which we have from sense, or which addresses itself to the sentient mind. All beyond this (according to him) is apprehended by the cogitant mind: all discrimination, comparison, and relation — such as the succession, or one, two, three, &c., of the separate impressions, the likeness of one stroke to the preceding, the contrast or dissimilarity of the black with the white — even the simplest acts of discrimination or comparison belong (in Plato’s view) to mental powers beyond and apart from sense; much more, of course, apprehension of the common properties of all, and of those extreme abstractions to which we apply the words Ens and Non-Ens (τό τ’ ἐπὶ πᾶσι κοινὸν καὶ τὸ ἐπὶ τούτοις, ᾧ τὸ ἔστιν ἐπονομάζεις καὶ τὸ οὐκ ἔστιν, p. 185 C).

When Plato thus narrows the sense of αἴσθησις, it is easy to prove that ἐπιστήμη is not αἴσθησις; but I doubt whether those who affirmed this proposition intended what he here refutes. Neither unreflecting men, nor early theorizers, would distinguish the impressions of sense from the feeling of such impressions being successive, distinct from one another, resembling, &c. Mr. John Stuart Mill observes (Logic, Book i. chap. iii. sects. 10-13) — “The simplest of all relations are those expressed by the words antecedent and consequent, and by the word simultaneous. If we say dawn preceded sunrise, the fact in which the two things dawn and sunrise were jointly concerned, consisted only of the two things themselves. No third thing entered into the fact or phenomenon at all, unless indeed we choose to call the succession of the two objects a third thing; but their succession is not something added to the things themselves, it is something involved in them. To have two feelings at all, implies having them either successively or simultaneously. The relations of succession and simultaneity, of likeness and unlikeness, not being grounded on any fact or phenomenon distinct from the related objects themselves, do not admit of the same kind of analysis. But these relations, though not (like other relations) grounded on states of consciousness, are themselves states of consciousness. Resemblance is nothing but our feeling of resemblance: succession is nothing but our feeling of succession.”

By all ordinary (non-theorising) persons, these familiar relations, involved in the facts of sense, are conceived as an essential part of αἴσθησις: and are so conceived by those modern theorists who trace all our knowledge to sense — as well as (probably) by those ancient theorists who defined ἐπιστήμη to be αἴσθησις, and against whom Plato here reasons. These theorists would have said (as ordinary language recognises) — “We see the dissimilarity of the black hands from the white face of the clock; we hear the likeness of one stroke of the clock to another, and the succession of the strokes one, two, three, one after the other”.

The reasoning of Plato against these opponents is thus open to many of the remarks made by Sir William Hamilton, in the notes to his edition of Reid’s works, upon Reid’s objections against Locke and Berkeley: Reid restricted the word Sensation to a much narrower meaning than that given to it by Locke and Berkeley. “Berkeley’s Sensation” (observes S. W. Hamilton) “was equivalent to Reid’s Sensation plus Perception. This is manifest even by the passages adduced in the text” (note to p. 289). But Reid in his remarks omits to notice this difference in the meaning of the same word. The case is similar with Plato when he refutes those who held the doctrine Ἐπιστήμη = Αἴσθησις. The last-mentioned word, in his construction, includes only a part of the meaning which they attributed to it; but he takes no notice of this verbal difference. Sir William Hamilton remarks, respecting M. Royer Collard’s doctrine, which narrows prodigiously the province of Sense, — “Sense he so limits that, if rigorously carried out, no sensible perception, as no consciousness, could be brought to bear”. This is exactly true about Plato’s doctrine narrowing αἴσθησις. See Hamilton’s edit. of Reid, Appendix, p. 844.

Aristotle understands αἴσθησις — αἰσθητικὴ ψυχὴ or ζωή — as occupying a larger sphere than that which Plato assigns to them in the Theætêtus. Aristotle recognises the five separate αἰσθήσεις, each correlating with and perceiving its ἴδιον αἰσθητόν: he also recognises ἡ κοινὴ αἴσθησις — common sensation or perception — correlating with (or perceiving) τὰ κοινὰ αἰσθητά, which are motion, rest, magnitude, figure, number. The κοινὴ αἴσθησις is not a distinct or sixth sense, apart from the five, but a general power inhering in all of them. He farther recognises αἴσθησις as discriminating, judging, comparing, knowing: this characteristic, τὸ κριτοκὸν and γνωστικόν, is common to αἴσθησις, φαντασία, νόησις, and distinguishes them all from appetite — τὸ ὀρεκτικόν, κινητικόν, &c. See the first and second chapters of the third Book of the Treatise De Animâ, and the Commentary of Simplikius upon that Treatise, especially p. 56, b. Aristotle tells us that all animals ἔχει δύναμιν σύμφυτον κριτικήν, ἣν καλοῦσιν αἴσθησιν. Anal. Poster. ii. p. 99, b. 35. And Sir William Hamilton adopts a similar view, when he remarks, that Judgment is implied in every act of Consciousness.

Occasionally indeed Aristotle partitions the soul between νοῦς and ὄρεξις — Intelligence and Appetite — recognising Sense as belonging to the head of Intelligence — see De Motu Animalium, 6, p. 700, b. 20. ταῦτα δὲ πάντα ἀνάγεται εἰς νοῦν καὶ ὄρεξιν· καὶ γὰρ ἡ φαντασία καὶ ἡ αἴσθησις τὴν αὐτὴν τῷ νῷ χώραν ἔχουσι· κριτικὰ γὰρ πάντα. Compare also the Topica, ii. 4, p. 111, a. 18.

It will thus be seen that while Plato severs pointedly αἴσθησις from anything like discrimination, comparison, judgment, even in the most rudimentary form — Aristotle refuses to adopt this extreme abstraction as his basis for classifying the mental phenomena. He recognises a certain measure of discrimination, comparison, and judgment, as implicated in sensible perceptions. Moreover, that which he calls κοινὴ αἴσθησις is unknown to Plato, who isolates each sense, and indeed each act of each sense, as much as possible. Aristotle is opposed, as Plato is, to the doctrine Ἐπιστήμη = Αἴσθησις, but he employs a different manner of reasoning against it. See, inter alia, Anal. Poster. i. 31, p. 87, b. 28. He confines ἐπιστήμη to one branch of the νοητική.

The Peripatetic Straton, the disciple of Theophrastus, denied that there was any distinct line of demarcation between τὸ αἰσθάνεσθαι and τὸ νοεῖν: maintaining that the former was impossible without a certain measure of the latter. His observation is very worthy of note. Plutarch, De Solertiâ Animalium, iii. 6, p. 961 A. Καίτοι Στράτωνός γε τοῦ φυσικοῦ λόγος ἐστίν, ἀποδεικνύων ὡς οὐδ’ αἰσθάνεσθαι τοπαράπαν ἄνευ τοῦ νοεῖν ὑπάρχει· καὶ γὰρ γράμματα πολλάκις ἐπιπορευόμενα τῇ ὄψει, καὶ λόγοι προσπίπτοντες τῇ ἀκοιῇ διαλανθάνουσιν ἡμᾶς καὶ διαφεύγουσι πρὸς ἑτέροις τὸν νοῦν ἔχοντας· εἶτ’ αὖθις ἐπανῆλθε καὶ μεταθεῖ καὶ μεταδιώκει τῶν προïεμένων ἕκαστον ἀναλεγόμενος· ᾗ καὶ λέλεκται. Νοῦς ὁρῇ, καὶ νοῦς ἀκούει, τὰ δὲ ἄλλα κωφὰ καὶ τυφλά· ὡς τοῦ περὶ τὰ ὄμματα καὶ ὦτα πάθους, ἂν μὴ παρῇ τὸ φρονοῦν, αἴσθησιν οὐ ποιοῦντος.

Straton here notices that remarkable fact (unnoticed by Plato and even by Aristotle, so far as I know) in the process of association, that impressions of sense are sometimes unheeded when they occur, but force themselves upon the attention afterwards, and are recalled by the mind in the order in which they occurred at first.