[25] Ibid. i. p. 402, b. 16, seq.; v. p. 409, b. 15.
[26] Ibid. ii. p. 403, b. 30.
Aristotle requires that a good theory of the soul shall explain alike the lowest vegetable soul, and the highest functions of the human or divine soul. And, in commenting on those theorists who declared that the essence of soul consisted in movement, he remarks that their theory fails altogether in regard to the Noûs (or cogitative and intellective faculty of the human soul); the operation of which bears far greater analogy to rest or suspension of movement than to movement itself.[27]
[27] Aristot. De Animâ, I. iii. p. 407, a. 32: ἔτι δ’ ἡ νόησις ἔοικεν ἠρεμήσει τινὶ ἢ ἐπιστάσει μᾶλλον ἢ κινήσει.
We shall now proceed to state how Aristotle steers clear (or at least believes himself to steer clear) of the defects that he has pointed out in the psychological theories of his predecessors. Instead of going back (like Empedokles, Plato, and others) to a time when the Kosmos did not yet exist, and giving us an hypothesis to explain how its parts came together or were put together, he takes the facts and objects of the Kosmos as they stand, and distributes them according to distinctive marks alike obvious, fundamental, and pervading; after which he seeks a mode of explanation in the principles of his own First Philosophy or Ontology. Whoever had studied the Organon and the Physica of Aristotle (apparently intended to be read prior to the treatise De Animâ) would be familiar with his distribution of Entia into ten Categories, of which Essence or Substance was the first and the fundamental. Of these Essences or Substances the most complete and recognized were physical or natural bodies; and among such bodies one of the most striking distinctions, was between those that had life and those that had it not. By life, Aristotle means keeping up the processes of nutrition, growth, and decay.[28]
[28] Ibid. II i. p. 412, a. 11: οὐσίαι δὲ μάλιστ’ εἶναι δοκοῦσι τὰ σώματα, καὶ τούτων τὰ φυσικά· τῶν δὲ φυσικῶν τὰ μὲν ἔχει ζωήν, τὰ δ’ οὐκ ἔχει· ζωὴν δὲ λέγω, τὴν δι’ αὐτοῦ τροφὴν καὶ αὔξησιν καὶ φθίσιν.
“To live� (Aristotle observes) is a term used in several different meanings; whatever possesses any one of the following four properties is said to live:[29] (1) Intellect, (2) Sensible perception, (3) Local movement and rest, (4) Internal movement of nutrition, growth, and decay. But of these four the last is the only one common to all living bodies without exception; it is the foundation presupposed by the other three. It is the only one possessed by plants,[30] and common to all plants as well as to all animals — to all animated bodies.
[29] Ibid. ii. p. 413, a. 22: πλεοναχῶς δὲ τοῦ ζῆν λεγομένου, κἂν ἕν τι τούτων ἐνυπάρχῃ μόνον, ζῆν αὐτό φαμεν, &c.
[30] Ibid. I. v. p. 411, b. 27, ad fin.
What is the animating principle belonging to each of these bodies, and what is the most general definition of it? Such is the problem that Aristotle states to himself about the soul.[31] He explains it by a metaphysical distinction first introduced (apparently) by himself into Philosophia Prima. He considers Substance or Essence as an ideal compound; not simply as clothed with all the accidents described in the nine last Categories, but also as being analysable in itself, even apart from these accidents, into two abstract, logical, or notional elements or principia — Form and Matter. This distinction is borrowed from the most familiar facts of the sensible world — the shape of solid objects. When we see or feel a cube of wax, we distinguish the cubic shape from the waxen material;[32] we may find the like shape in many other materials — wood, stone, &c.; we may find the like material in many different shapes — sphere, pyramid, &c.; but the matter has always some shape, and the shape has always some matter. We can name and reason about the matter, without attending to the shape, or distinguishing whether it be cube or sphere; we can name and reason about the shape, without attending to the material shaped, or to any of its various peculiarities. But this, though highly useful, is a mere abstraction or notional distinction. There can be no real separation between the two: no shape without some solid material; no solid material without some shape. The two are correlates; each of them implying the other, and neither of them admitting of being realized or actualized without the other.