[73] Aristot. De Animâ, II. vi. p. 418, a. 10-16.
[74] Aristot. De Sensu et Sensili, i. p. 437, a. 8; iv. p. 442, b. 4-12. He says in this last passage, that the common perceivables are appreciable at least by both sight and touch — if not by all the senses.
[75] Aristot. De Animâ, II. vi. p. 418, a. 7-25: λέγεται δὲ τὸ αἰσθητὸν τριχῶς, ὧν δύο μὲν καθ’ αὑτά φαμεν αἰσθάνεσθαι, τὸ δὲ ἓν κατὰ συμβεβηκός. Also, III. i. p. 425, b. 24; iii. p. 428, b. 18-25.
Among the five senses, Aristotle distinguishes two as operating by direct contact between subject and object (touch, taste); three as operating through an external intervening medium (vision, smell, taste). He begins with Vision, which he regards as possessing most completely the nature and characteristics of a sense.[76] The direct and proper object of vision is colour. Now colour operates upon the eye not immediately (for, if the coloured object be placed in contact with the eye, there will be no vision), but by causing movements or perturbations in the external intervening medium, air or water, which affect the sense through an appropriate agency of their own.[77] This agency is, according to Aristotle, the Diaphanous or Transparent. When actual or in energy, the transparent is called light; when potential or in capacity only, it is called darkness. The eye is of watery structure, apt for receiving these impressions.[78] It is the presence either of fire, or of something analogous to the celestial body, that calls forth the diaphanous from the state of potentiality into that of actuality or light; in which latter condition it is stimulated by colour. The diaphanous, whether as light or as darkness, is a peculiar nature or accompaniment, not substantive in itself, but inherent chiefly in the First or Celestial Body, yet also in air, water, glass, precious stones, and in all bodies to a greater or less degree.[79] The diaphanous passes at once and simultaneously, in one place as well as in another, from potentiality to actuality — from darkness to light. Light does not take time to travel from one place to another, as sound and smell do.[80] The diaphanous is not a body, nor effluvium from a body, nor any one of the elements: it is of an adjective character — a certain agency or attribute pervading or belonging to bodies, along with their extension.[81] Colour marks and defines the surface of the body quâ diaphanous, as figure defines it quâ extended. Colour makes the diaphanous itself visible, and its own varieties visible through the diaphanous. Air and water are transparent throughout, though with an ill-defined superficial colour. White and black, as colours in solid bodies, correspond to the condition of light or darkness in air. There are some luminous objects visible in the dark, as fire, fungous matter, eyes, and scales of fish, &c., though they have no appropriate colour.[82] There are seven species or varieties of colours, but all of them proceed from white and black, blended in different proportions, or seen one through another; white and black are the two extremes, the other varieties being intermediate between them.
[76] Aristot. De Animâ, III. iii. p. 429, a. 2: ἡ ὄψις μάλιστα αἰσθησίς ἐστιν. Also Metaphysica, A. init.
[77] Aristot. De Animâ, II. vii. p. 419, a. 12, 14, 19; Aristot. De Sensu et Sensili, iii. p. 440, a. 18: ὥστ’ εὐθὺς κρεῖττον φάναι, τῷ κινεῖσθαι τὸ μεταξὺ τῆς αἰσθήσεως ὑπὸ τοῦ αἰσθητοῦ γίνεσθαι τὴν αἴσθησιν, ἁφῇ καὶ μὴ ταῖς ἀποῤῥοίαις. — Ib. ii. p. 438, b. 3: εἴτε φῶς εἴτ’ ἀήρ ἐστι τὸ μεταξὺ τοῦ ὁρωμένου καὶ τοῦ ὄμματος, ἡ διὰ τούτου κίνησίς ἐστιν ἡ ποιοῦσα τὸ ὁρᾶν.
[78] Aristot. De Animâ, II. vii. p. 419, a. 9: τοῦτο γὰρ ἦν αὐτῷ τὸ χρώματι εἶναι, τὸ κινητικῷ εἶναι τοῦ κατ’ ἐνέργειαν διαφανοῦς φῶς ἐστίν. — Ib. ii. p. 418, b. 11-17: ὅταν ᾖ ἐντελεχείᾳ διαφανὲς ὑπὸ πυρὸς ἢ τοιούτου οἷον τὸ ἄνω σῶμα· — πυρὸς ἢ τοιούτου τινὸς παρουσία ἐν τῷ διαφανεῖ.
[79] Aristot. De Animâ, II. vii. p. 418, b. 4. De Sensu et Sensili, ii. p. 438, a. 14, b. 7; iii. p. 439, a. 21, seq.: ὃ δὲ λέγομεν διαφανές, οὐκ ἔστιν ἴδιον ἀέρος ἢ ὕδατος, οὐδ’ ἄλλου τῶν οὕτω λεγομένων σωμάτων, ἀλλά τίς ἐστὶ κοινὴ φύσις καὶ δύναμις, ἣ χωριστὴ μὲν οὐκ ἔστιν, ἐν τούτοις δ’ ἐστί, καὶ τοῖς ἄλλοις σώμασιν ἐνυπάρχει, τοῖς μὲν μᾶλλον τοῖς δ’ ἧττον.
[80] Aristot. De Sensu et Sensili, vi. p. 446, a. 23, seq., b. 27: τῷ εἶναι γάρ τι φῶς ἐστίν, ἀλλ’ οὐ κίνησίς τις. Empedokles affirmed that light travelling from the Sun reached the intervening space before it came to the earth; Aristotle contradicts him.
[81] Aristot. De Animâ, II. vii. p. 418, b. 18: ἔστι δὲ τὸ σκότος στέρησις τῆς τοιαύτης ἕξεως ἐκ διαφανοῦς, ὥστε δῆλον ὅτι καὶ ἡ τούτου παρουσία φῶς ἐστίν. — Aristot. De Sensu et Sensili, iii. p. 439, a. 26: ἡ μὲν οὖν τοῦ φωτὸς φύσις ἐν ἀὀρίστῳ τῷ διαφανεῖ ἐστίν· τοῦ δ’ ἐν τοῖς σώμασι διαφανοῦς τὸ ἔσχατον, ὅτι μὲν εἴη ἄν τι, δῆλον· ὅτι δὲ τοῦτο ἐστὶ τὸ χρῶμα, ἔκ τῶν συμβαινόντων φανερόν. — ἔστι μὲν γὰρ ἐν τῷ τοῦ σώματος πέρατι, ἀλλ’ οὔ τι τὸ τοῦ σώματος πέρας, ἀλλὰ τὴν αὐτὴν φύσιν δεῖ νομίζειν, ἥπερ καὶ ἔξω χρωματίζεται, ταύτην καὶ ἐντός.