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.
[100] Plato, Theæt. p. 187 A. Sokr. ὅμως δὲ τοσοῦτόν γε προβεβήκαμεν, ὥστε μὴ ζητεῖν αὐτὴν (ἐπιστήμην) ἐν αἰσθήσει τοπαράπαν, ἀλλ’ ἐν ἐκείνῳ τῷ ὀνόματι, ὅ, τι ποτ’ ἔχει ἡ ψυχή, ὅταν αὐτὴ καθ’ αὑτὴν πραγματεύηται περὶ τὰ ὄντα. Theæt. Ἀλλὰ μὴν τοῦτό γε καλεῖται, ὡς ἐγᾦμαι, δοξάζειν. Sokr. Ὀρθῶς γὰρ οἴει.
Plato is quite right in distinguishing between αἴσθησις and δόξα, looking at the point as a question of psychological classification. It appears to me, however, most probable that those who maintained the theory Ἐπιστήμη = Αἴσθησις, made no such distinction, but included that which he calls δόξα in αἴσθησις. Unfortunately we do not possess their own exposition; but it cannot have included much of psychological analysis.
[101] Schleiermacher represents Plato as discriminating Knowledge (the region of infallibility, you either possess it or not) from Opinion (the region of fallibility, true or false, as the case may be) by a broad and impassable line —