The extent of Potentiality, or the partial Actuality, which Aristotle claims for the sentient soul even at birth, deserves to be kept in mind; we shall contrast it presently with what he says about the Noûs.
[67] Aristot. De Animâ, II. v. p. 417, b. 22: αἴτιον δὲ ὅτι, τῶν καθ’ ἕκαστον ἡ κατ’ ἐνέργειαν αἴσθησις, ἡ δ’ ἐπιστήμη τῶν καθόλου· ταῦτα δ’ ἐν αὐτῇ πώς ἐστι τῇ ψυχῇ. III. iii. p. 427, b. 18.
We have already remarked, that in many animals the sentient soul is little developed; being confined in some to the sense of touch (which can never be wanting),[68] and in others to touch and taste. But even this minimum of sense — though small, if compared with the variety of senses in man — is a prodigious step in advance of plants; it comprises a certain cognition, and within its own sphere it is always critical, comparing, discriminative.[69] The sentient soul possesses this discriminative faculty in common with the noëtic soul or Intelligence, though applied to different objects and purposes; and possesses such faculty, because it is itself a mean or middle term between the two sensible extremes of which it takes cognizance, — hot and cold, hard and soft, wet and dry, white and black, acute and grave, bitter and sweet, light and darkness, visible and invisible, tangible and intangible, &c. We feel no sensation at all when the object touched is exactly of the same temperature with ourselves, neither hotter nor colder; the sentient soul, being a mean between the two extremes, is stimulated to assimilate itself for the time to either of them, according as it is acted upon from without. It thus makes comparison of each with the other, and of both with its own mean.[70] Lastly, the sentient faculty in the soul is really one and indivisible, though distinguishable logically or by abstraction into different genera and species.[71] Of that faculty the central physical organ is the heart, which contains the congenital or animal spirit. The Aristotelian psychology is here remarkable, affirming as it does the essential relativity of all phenomena of sense to the appreciative condition of the sentient; as well as the constant implication of intellectual and discriminative comparison among them.
[68] Ibid. III. xii. p. 434, b. 23: φανερὸν ὅτι οὐχ οἷόν τε ἄνευ ἁφῆς εἶναι ζῷον.
[69] Ibid. ix. p. 432, a. 16: τῷ κριτικῷ, ὃ διανοίας ἔργον ἐστὶ καὶ αἰσθήσεως. — III. iii. p. 427, a. 20; p. 426, b. 10-15. De Generat. Animal. I. xxiii. p. 731, a. 30-b. 5; De Somno et Vigil. i. p. 458, b. 2. The sentient faculty is called δύναμιν σύμφυτον κριτικήν in Analyt. Poster. II. xix. p. 99, b. 35.
[70] Aristot. De Animâ, II. x. p. 422, a. 20; ix. p. 421, b. 4-11; xi. p. 424, a. 5: καὶ διὰ τοῦτο κρίνει τὰ αἰσθητά â€” τὸ γὰρ μέσον κριτικόν. III. vii. p. 431, a. 10: ἔστι τὸ ἥδεσθαι καὶ λυπεῖσθαι τὸ ἐνεργεῖν τῇ αἰσθητικῇ μεσότητι πρὸς τὸ ἀγαθὸν ἢ κακόν, ᾗ τοιαῦτα. III. xiii. p. 435, a. 21.
He remarks that plants have no similar μεσότης — II. xii. p. 424, b. 1.
[71] Aristot. De Sensu et Sensili, vii. p. 449, a. 8, 17. De Motu Animal. x. p. 703, a. 15. De Somno et Vigil. ii. p. 455, a. 15, 21, 35; p. 456, a. 5. De Juventute et Senect. p. 467, b. 27; p. 469, a. 4-12.
All the objects generating sensible perception, are magnitudes.[72] Some perceptions are peculiar to one sense alone, as colour to the eye, &c. Upon these we never make mistakes directly; in other words, we always judge rightly what is the colour or what is the sound, though we are often deceived in judging what the thing coloured is, or where the sonorous object is.[73] There are, however, some perceivables not peculiar to any one sense alone, but appreciable by two or more; though chiefly and best by the sense of vision; such are motion, rest, number, figure, magnitude. Here the appreciation becomes less accurate, yet it is still made directly by sense.[74] But there are yet other matters that, though not directly affecting sense, are perceived indirectly, or by way of accompaniment to what is directly perceived. Thus we see a white object; nothing else affecting our sense except its whiteness. Beyond this, however, we judge and declare, that the object so seen is the son of Kleon. This is a judgment obtained indirectly, or by way of accompaniment; by accident, so to speak, inasmuch as the same does not accompany all sensations of white. It is here that we are most liable to error.[75]
[72] Aristot. De Sensu et Sensili, vii. p. 449, a. 20: τὸ αἰσθητὸν πᾶν ἐστὶ μέγεθος.