[95] Plato, Theætêt. p. 185 D. δοκεῖ τὴν ἀρχὴν οὐδ’ εἶναι τοιοῦτον οὐδὲν τούτοις ὄργανον ἴδιον, ὥσπερ ἐκείνοις, ἀλλ’ αὐτὴ δι’ αὑτῆς ἡ ψυχὴ τὰ κοινά μοι φαίνεται περὶ πάντων ἐπισκοπεῖν.
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.
[96] Plato, Theætêt. p. 186 B. Τὴν δέ γε οὐσίαν καὶ ὅ τι ἔστον καὶ τὴν ἐναντιότητα πρὸς ἀλλήλω (of hardness and softness) καὶ τὴν οὐσίαν αὖ τῆς ἐναντιότητος, αὐτὴ ἡ ψυχὴ ἐπανιοῦσα καὶ ξυμβάλλουσα πρὸς ἄλληλα κρίνειν πειρᾶται ἡμῖν … Οὐκοῦν τὰ μὲν εὐθὺς γενομένοις πάρεστι φύσει αἰσθάνεσθαι ἀνθρώποις τε καὶ θηρίοις, ὅσα διὰ τοῦ σώματος παθήματα ἐπὶ τὴν ψυχὴν τείνει· τὰ δὲ περὶ τούτων ἀναλογίσματα, πρός τε οὐσίαν καὶ ὠφελείαν μόγις καὶ ἐν πολλῷ χρόνῳ διὰ πολλῶν πραγμάτων καὶ παιδείας παραγίγνεται, οἷς ἂν καὶ παραγίγνηται.
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]
[97] Plato, Theætêt. p. 186 D. ἐν μὲν ἄρα τοῖς παθήμασιν οὐκ ἔνι ἐπιστήμη, ἐν δὲ τῷ περὶ ἐκείνων συλλογισμῷ· οὐσίας γὰρ καὶ ἀληθείας ἐνταῦθα μέν, ὡς ἔοικε, δυνατὸν ἅψασθαι, ἐκεῖ δὲ ἀδύνατον. The term συλλογισμὸς is here interesting, before it had received that technical sense which it has borne from Aristotle downwards. Mr. Campbell explains it properly as “nearly equivalent to abstraction and generalisation” (Preface to Theætêtus, p. lxxiv., also note, p. 144).
[98] Plato, Theætêt. p. 186 A. καλὸν καὶ αἰσχρόν, καὶ ἀγαθὸν καὶ κακόν. Καὶ τούτων μοι δοκεῖ ἐν τοῖς μάλιστα πρὸς ἄλληλα σκοπεῖσθαι τὴν οὐσίαν, ἀναλογιζομένη (ἡ ψυχὴ) ἐν ἑαυτῇ τὰ γεγονότα καὶ τὰ παρόντα πρὸς τὰ μέλλοντα.
Base and honourable, evil and good, are here pointed out by Sokrates as most evidently and emphatically relative. In the train of reasoning here terminated, Plato had been combating the doctrine Αἴσθησις = Ἐπιστήμη. In his sense of the word αἴσθησις he has refuted the doctrine. But what about the other doctrine, which he declares to be a part of the same programme — Homo Mensura — the Protagorean formula? That formula, so far from being refuted, is actually sustained and established by this train of reasoning. Plato has declared οὐσία, ἀληθεία, ἐναντιότης, ἀγαθόν, κακόν, &c., to be a distinct class of Objects not perceived by Sense. But he also tells us that they are apprehended by the Mind through its own working, and that they are apprehended always in relation to each other. We thus see that they are just as much relative to the concipient mind, as the Objects of sense are to the percipient and sentient mind. The Subject is the correlative limit or measure (to use Protagorean phrases) of one as well as of the other. This confirms what I observed above, that the two doctrines, 1. Homo Mensura, 2. Αἴσθησις = Ἐπιστήμη, — are completely distinct and independent, though Plato has chosen to implicate or identify them.
Examination of this view — Distinction from the views of modern philosophers.