We have seen above the Aristotelian distinction between the active intellect and the passive. The account just given is evidently based upon it, though it modifies Aristotle's analysis, or rather it enlarges upon it. The first and second divisions in Israeli's account correspond to Aristotle's active and passive intellects respectively. The third class in Israeli represents the process of realization of the potential or passive intellect through the sense stimuli on the one hand and the influence of the active intellect on the other. Aristotle seems to have left this intermediate state between the potential and the eternally actual unnamed. We shall see, however, in our further study of this very difficult and complicated subject how the classification of the various intellects becomes more and more involved from Aristotle through Alexander and Themistius down to Averroes and Levi ben Gerson. It is sufficient for us to see here how Israeli combines Aristotelian psychology, as later Aristotelian logic and physics, with Neo-Platonic metaphysics and the theistic doctrine of creation. But more of this hereafter.
From the Intelligence, as we have seen, proceeds the rational soul. In his discussion of the general nature of the three-fold soul (rational, animal and vegetative) Israeli makes the unhistoric but thoroughly mediæval attempt to reconcile Aristotle's definition of the soul, which we discussed above (p. xxxv), with that of Plato. The two conceptions are in reality diametrically opposed. Plato's is an anthropological dualism, Aristotle's, a monism. For Plato the soul is in its origin not of this world and not in essential unity with the body, which it controls as a sailor his boat. Aristotle conceives of the relation between soul and body as one of form and matter; and there is no union more perfect than that of these two constituent elements of all natural substances. Decomposition is impossible. A given form may disappear, but another form immediately takes its place. The combination of matter and form is the essential condition of sublunar existence, hence there can be no question of the soul entering or leaving the body, or of its activity apart from the body.