Anaxagoras, Demokritus, and other philosophers, appear to have spoken of Noûs or Intellect in a large and vague sense, as equivalent to Soul generally. Plato seems to have been the first to narrow and specialize the meaning; distinguishing pointedly (as we have stated above) the rational or encephalic soul, in the cranium, with its circular rotations, from the two lower souls, thoracic and abdominal. Aristotle agreed with him in this distinction (either of separate souls or of separate functions in the same soul); but he attenuated and divested it of all connexion with separate corporeal lodgment, or with peculiar movements of any kind. In his psychology, the brain no longer appears as the seat of intelligence, but simply as a cold, moist, and senseless organ, destined to countervail the excessive heat of the heart: which last is the great centre of animal heat, of life, and of the sentient soul. Aristotle declares Noûs not to be connected with, or dependent on, any given bodily organs or movements appropriated to itself: this is one main circumstance distinguishing it from the nutrient soul as well as from the sentient soul, each of which rests indispensably upon corporeal organs and agencies of its own.
It will be remembered that we stated the relation of Soul to Body (in Aristotle’s view) as that of Form to Matter; the two together constituting a concrete individual, numerically one; also that Form and Matter, each being essentially relative to the other, admitted of gradations, higher and lower; e.g. a massive cube of marble is already materia formata, but it is still purely materia, relative to the statue that may be obtained from it. Now, the grand region of Form is the Celestial Body — the vast, deep, perceivable, circular mass circumscribing the Kosmos, and enclosing, in and around its centre, Earth with the other three elements, tenanted by substances generated and perishable. This Celestial Body is the abode of divinity, including many divine beings who take part in its eternal rotations, viz. the Sun, Moon, Stars, &c., and other Gods. Now, every soul, or every form that animates the matter of a living being, derives its vitalizing influence from this celestial region. All seeds of life include within them a spiritual or gaseous heat, more divine than the four elements, proceeding from the sun, and in nature akin to the element of the stars. Such solar or celestial heat differs generically from the heat of fire. It is the only source from whence the principle of life, with the animal heat that accompanies it, can be obtained. Soul, in all its varieties, proceeds from hence.[145]
[145] Aristot. De Generat. Animal. II. iii. p. 736, b. 29: πάσης μὲν οὖν ψυχῆς δύναμις ἑτέρου σώματος ἔοικε κεκοινωνηκέναι καὶ θειοτέρου τῶν καλουμένων στοιχείων· ὡς δὲ διαφέρουσι τιμιότητι αἱ ψυχαὶ καὶ ἀτιμίᾳ ἀλλήλων, οὕτω καὶ ἡ τοιαύτη διαφέρει φύσις· πάντων μὲν γὰρ ἐν τῷ σπέρματι ἐνυπάρχει, ὅπερ ποιεῖ γόνιμα εἶναι τὰ σπέρματα, τὸ καλούμενον θερμόν.
But though all varieties of Soul emanate from the same celestial source, they possess the divine element in very different degrees, and are very unequal in comparative worth and dignity. The lowest variety, or nutritive soul — the only one possessed by plants, among which there is no separation of sex[146] — is contained potentially in the seed, and is thus transmitted when that seed is matured into a new individual. In animals, which possess it along with the sensitive soul and among which the sexes are separated, it is also contained potentially in the generative system of the female separately; and the first commencement of life in the future animal is thus a purely vegetable life.[147] The sensitive soul, the characteristic of the complete animal, cannot be superadded except by copulation and the male semen. The female, being comparatively impotent and having less animal heat, furnishes only the matter of the future offspring; form, or the moving, fecundating, cause, is supplied by the male. Through the two together the new individual animal is completed, having not merely the nutritive soul, but also the sentient soul along with it.[148]
[146] Ibid. I. xxiii. p. 731, a. 27.
[147] Aristot. De Generat. Animal. II. iii. p. 736, b. 12.
[148] Ibid. I. ii. p. 716, a. 4-17; xix. p. 726, b. 33; xx. p. 728, a. 17; xxi. p. 729, b. 6-27.
Both the nutritive and the sentient souls have, each of them respectively, a special bodily agency and movement belonging to them. But the Noûs, or the noëtic soul, has no partnership with any similar bodily agency. There is no special corporeal potentiality (to speak in Aristotelian language) which it is destined to actualize. It enters from without, and emanates from a still more exalted influence of that divine celestial substance from which all psychical or vitalizing heat proceeds.[149] It is superinduced upon the nutritive and sentient souls, and introduces itself at an age of the individual later than both of them. Having no part of the bodily organism specially appropriated to it, this variety of soul — what is called the Noûs — stands distinguished from the other two in being perfectly separable from the body;[150] that is, separable from the organized body which it is the essential function of the two lower souls to actualize, and with which both of them are bound up. The Noûs is not separable from the body altogether; it belongs essentially to the divine celestial body, and to those luminaries and other divine beings by whom portions of it are tenanted. Theorizing contemplation — the perfect, unclouded, unembarrassed, exercise of the theoretical Noûs — is the single mental activity of these divinities; contemplation of the formal regularity of the Kosmos, with its eternal and faultless rotations, and with their own perfection as participating therein. The celestial body is the body whereto Noûs, or the noëtic soul, properly belongs;[151] quite apart from the two other souls, sentient and nutritive, upon which it is grafted in the animal body; and apart also from all the necessities of human action, preceded by balanced motives and deliberate choice.[152]
[149] Ibid. II. iii. p. 736, b. 27: λείπεται δὲ τὸν νοῦν μόνον θύραθεν ἐπεισιέναι, καὶ θεῖον εἶναι μόνον· οὐθὲν γὰρ αὐτοῦ τῇ ἐνεργείᾳ κοινωνεῖ σωματικὴ ἐνέργεια. The words θεῖον εἶναι μόνον must not be construed strictly, for in the next following passage he proceeds to declare that all ψυχή, ψυχικὴ δύναμις or ἀρχή, partakes of the divine element, and that in this respect there is only a difference of degree between one ψυχὴ and another.
[150] Ibid. p. 737, a. 10: ὁ καλούμενος νοῦς. De Animâ, II. ii. p. 413, b. 25; iii. p. 415, a. 11.