Note 43 — Chapter XXVIII · THEÆTETUS.

Aristotle, in a passage of the treatise De Animâ (iii. 1, 2-4-7-8, ed. Trendelenburg, p. 425, b. 25, p. 426, a. 15-25, Bekk.), impugns an opinion of certain antecedent φυσιόλογοι whom he does not specify; which opinion seems identical with the doctrine of Protagoras. These philosophers said, that “there was neither white nor black without vision, nor savour without the sense of taste”. Aristotle says that they were partly right, partly wrong. They were right in regard to the actual, wrong in regard to the potential. The actual manifestation of the perceived is one and the same with that of the percipient, though the two are not the same logically in the view of the reflecting mind (ἡ δὲ τοῦ αἰσθητοῦ ἐνέργεια καὶ τῆς αἰσθήσεως ἡ αὐτὴ μέν ἐστι καὶ μία, τὸ δ’ εἶναι οὐ ταὐτὸν αὐταῖς). But this is not true when we speak of them potentially — διχῶς γὰρ λεγομένης τῆς αἰσθήσεως καὶ τοῦ αἰσθητοῦ, τῶν μὲν κατὰ δύναμιν τῶν δὲ κατ’ ἐνέργειαν, ἐπί τούτων μὲν συμβαίνει τὸ λεχθέν, ἐπὶ δὲ τῶν ἑτέρων οὐ συμβαίνει. Ἀλλ’ ἐκεῖνοι ἁπλῶς ἔλεγον περὶ τῶν λεγομένων οὐχ ἁπλῶς.

I think that the distinction, which Aristotle insists upon as a confutation of these philosophers, is not well founded. What he states, in very just language, about actual perception is equally true about potential perception. As the present fact of actual perception implicates essentially a determinate percipient subject with a determinate perceived object, and admits of being looked at either from the one point of view or from the other — so the concept of potential perception implicates in like manner an indeterminate perceivable with an indeterminate subject competent to perceive. The perceivable or cogitable has no meaning except in relation to some Capax Percipiendi or Capax Cogitandi.