Plato's Sophist [159-160]

All deliberating ends in an αἴσθησις. This straightforward perceiving within φρόνησις is νοῦς. Aristotle explicates the character of this αἴσθησις in the same book of the Nicomachean Ethics, chapter 9.

b) Practical νοῦς and αἴσθησις (Nic. Eth. VI, 9, III, 5).
Αἴσθησις as the grasping of the ἔσχατα. Comparison with
ἀνάλυσις in geometry. Modes of αἴσθησις. Geometrical and
practical αἴσθησις.

ὁ μὲν γὰρ νοῦς τῶν ὅρων, ὧν οὐκ ἔστι λόγος, ἣ δὲ τοῦ ἐσχάτου, οὗ οὐκ ἔστιν ἐπιστήμη ἀλλ' αἴσθησις, οὐχ ἡ τῶν ἰδίων, ἀλλ' οἵᾳ αἰσθανόμεθα ὅτι τὸ ἐν τοῖς μαθηματικοῖς ἔσχατον τρίγωνον· στήσεται γὰρ κἀκεῖ. (Nic. Eth. VI, 9, 1142a25ff.). In φρόνησις, the states of affairs are grasped purely, as they show themselves. Such grasping is a matter of perception, αἴσθησις. This perception, however, does not relate to the specific objects of perceiving in the strictest sense, to the ἴδια of αἴσθησις. In Book II, chapter 6, of the De Anima, Aristotle explains what these ἴδια αἰσθητά are: λέγω δ' ἴδιον μὲν ὃ μὴ ἐνδέχεται ἑτέρα αἰσθήσει αἰσθάνεσθαι καὶ περὶ ὃ μὴ ἐνδέχεται ἀπατηθῆναι (418a11f.). The ἴδια αἰσθητά are the objects that correspond respectively to seeing, hearing, smelling, etc. The ἴδιον of seeing is color, of hearing tone, etc. These ἴδια are ἀεὶ ἀληθῆ for the corresponding αἰσθήσεις. Aristotle distinguishes these ἴδια αἰσθητά from the κοινὰ αἰσθητά. The latter are κοινὰ πάσαις (a19), objects of perception which are common to all αἰσθήσεις, as, e.g., σχῆμα and μέγεθος, which can be perceived by various αἰσθήσεις.

Concerning now φρόνησις and the straightforward grasping of the ἔσχατον, where πρᾶξις intervenes, there it is a matter not of such an αἴσθησις, i.e., one which is τῶν ἰδίων, but of αἴσθησις in the broadest sense of the word, as it is commonly given in everyday existence. In αἴσθησις I see states of affairs as a whole, whole streets, houses, trees, people, and precisely in such a way that this αἴσθησις at the same time has the character of a simple constatation. It is a matter of an αἴσθησις such as the one with whose help we perceive ὅτι τὸ ἐν τοῖς μαθηματικοῖς ἔσχατον τρίγωνον (Nic. Eth. VI, 9, 1142a28f.), an αἴσθησις such as the one which, for example, plays a fundamental role in geometry, where it grasps the ἔσχατον of geometry: τρίγωνον. It must be noted here that in Greek geometry the triangle is the ultimate, most elementary plane figure, which emerges out of the polygon by means of a διαγράφειν, "writing through." Διαγράφειν analyzes the polygons until they are taken apart in simple triangles, in such a way that the triangles are the ἔσχατα where the διαιρεῖν stops.