[53] Aristot. De Animâ, I. v. p. 411, b. 28.
[54] Ibid. II. ii. p. 413, a. 25-30, b. 32; iii. p. 414, b. 29; p. 415, a. 10.
We may remark here that the psychological classification of Aristotle proceeds in the inverse direction to that of Plato. In the Platonic Timæus we begin with the grand soul of the Kosmos, and are conducted by successive steps of degradation to men, animals, plants; while Aristotle lays his foundation in the largest, most multiplied, and lowest range of individuals, carrying us by successive increase of conditions to the fewer and the higher.
The lowest or Nutritive soul, in spite of the small number of conditions involved in it, is the indispensable basis whereon all the others depend. None of the other souls can exist apart from it.[55] It is the first constituent of the living individual — the implication of Form with Matter in a natural body suitably organized; it is the preservative of the life of the individual, with its aggregate of functions and faculties, and with the proper limits of size and shape that characterize the species;[56] it is, moreover, the preservative of perpetuity to the species, inasmuch as it prompts and enables each individual to generate and leave behind a successor like himself; which is the only way that an individual can obtain quasi-immortality, though all aspire to become immortal.[57] This lowest soul is the primary cause of digestion and nutrition. It is cognate with the celestial heat, which is essential also as a co-operative cause; accordingly, all animated bodies possess an inherent natural heat.[58]
[55] Ibid. iv. p. 415, a. 25: πρώτη καὶ κοινοτάτη δύναμίς ἐστι ψυχῆς, καθ’ ἣν ὑπάρχει τὸ ζῆν ἅπασιν. — p. 415, b. 8: τοῦ ζῶντος σώματος αἰτία καὶ ἀρχή. — III. xii. p. 434, a. 22-30, b. 24. Aristot. De Respiratione, viii. p. 474, a. 30, b. 11.
[56] Aristot. De Animâ, II. iv. p. 416, a. 17.
[57] Ibid. p. 415, b. 2; p. 416, b. 23: ἐπεὶ δ’ ἀπὸ τοῦ τέλους ἅπαντα προσαγορεύειν δίκαιον, τέλος δὲ τὸ γεννῆσαι οἷον αὐτό, ἂν ἡ πρώτη ψυχὴ γεννητικὴ οἷον αὐτό. Also De Generat. Animal. II. i. p. 731, b. 33.
[58] Aristot. De Animâ, II. iv. p. 416, a. 10-18, b. 29.
We advance upwards now from the nutritive soul to that higher soul which is at once nutritive and Sentient; for Aristotle does not follow the example of Plato in recognizing three souls to one body, but assigns only one and the same soul, though with multiplied faculties and functions, to one and the same body. Sensible perception, with its accompaniments, forms the characteristic privilege of the animal as contrasted with the plant.[59] Sensible perception admits of many diversities, from the simplest and rudest tactile sensation, which even the lowest animals cannot be without, to the full equipment of five senses which Aristotle declares to be a maximum not susceptible of increase.[60] But the sentient faculty, even in its lowest stage, indicates a remarkable exaltation of the soul in its character of form. The soul, quâ sentient and percipient, receives the form of the perceptum without the matter; whereas the nutritive soul cannot disconnect the two, but receives and appropriates the nutrient substance, form and matter in one and combined.[61] Aristotle illustrates this characteristic feature of sensible perception by recurring to his former example of the wax and the figure. Just as wax receives from a signet the impression engraven thereon, whether the matter of the signet be iron, gold, stone, or wood; as the impression stamped has no regard to the matter, but reproduces only the figure engraven on the signet, the wax being merely potential and undefined, until the signet comes to convert it into something actual and definite;[62] so the percipient faculty in man is impressed by the substances in nature, not according to the matter of each but, according to the qualitative form of each. Such passive receptivity is the first and lowest form of sensation,[63] not having any magnitude in itself, but residing in bodily organs which have magnitude, and separable from them only by logical abstraction. It is a potentiality, correlating with, and in due proportion to, the exterior percipibile, which, when acting upon it, brings it into full actuality. The actuality of both (percipiens and perceptum) is one and the same, and cannot be disjoined in fact, though the potentialities of the two are distinct yet correlative; the percipiens is not like the percipibile originally, but becomes like it by being thus actualized.[64]
[59] Aristot. De Sensu et Sensili, i. p. 436, b. 12. He considers sponges to have some sensation (Hist. Animal. I. i. p. 487, b. 9).