The perplexing distinction between "active" and "passive" rea son has caused endless trouble to Aristotle's interpreters. In so far as it has relation to the other faculties of the soul, reason, so Aristotle would seem to say, must be contemplated from the point of view appropriate to all the world of generation as exhibiting the contrast between the potential and the actual. Obviously, indeed, reason is not constantly active in the human subject, and yet in its own nature it is nothing but activity. The limitation of its exercise in man must, therefore, be dependent on the fact that it is only realised under conditions connected with the life of the soul; in man, vas exists potentially until called into exer cise. What calls it into exercise, Aristotle affirms, is the presence of the intelligible (TO ponrop) exhibited in sense and its con comitant faculties.
Hence the activity of vas consists in the simple apprehension of the abstract essence ; the vonrOP may present itself as existing in the particulars, but as grasped by pas it is a simple essence, and holds the same relation to Pas as the sensible holds to sense. Accordingly, there is postulated at both ends of the scale a mode of cognition wholly distinct from discursive thinking. At the one end, there is a kind of apprehension which is free from the antith esis of true and false; the first principles must either be just ap prehended or not at all. At the other end likewise. sense-percep tion as such does not admit of the antithesis true or false ; the sense-particular must either be just apprehended or not at all.
Thus, the whole realm of demonstrable knowledge lay for Aris toile between the particulars (ra KaO' gKaara) on the one hand, and the primary, undemonstrable principles (the rpc7n-a Kai &Accra) on the other. The business of science was to connect these two extremes, for the great body of knowledge consists neither of the crudely apprehended data of sense nor of purely appre hended essences. Scientific demonstration, et7r6oats, is reasoning which proceeds from true and necessary premises and yields a con clusion which is, therefore, at once true and necessary and de terminate of the essence. Since any concrete thing or TO& TL is what it is by reason of its general character, complete knowledge of it would be obtained if we were able to connect all its features with the primitive components of its essence. But Aristotle recog nised with Plato that the particular has in it something which re sists perfect reduction to scientific generality,—the factor, namely, which in the metaphysical analysis is described as matter (an).
Apodictic was not, however, conceived by Aristotle in Platonic fashion as a method of deduction from one set of universally valid principles. It is characteristic of his view that, in addition to the common or general principles (KoLvai apxai), of which the most fundamental is the principle of contradiction, each distinct kind of fact, has its own special principles (Mac apxal), on which all demonstration respecting it must be based, or about which all demonstration turns.
It is equally characteristic of Aristotle that he should recognise the two-fold manner in which we approach the problem of obtain ing scientific knowledge, whether by apprehending isolated facts and so by comparison, rejection and the like, attaining an insight into what is universal, or by deductive procedure from already established or assumed universals. The world may be regarded in respect to knowledge under two aspects, (a) as a multiplicity of particulars, and (b) as a system of general laws on which the par ticulars depend. To the individual knower the particulars stand relatively nearer than the universal laws; they are the more easily cognised from his point of view. They are rpOs nyeis rpOrEpa, prior and better known relatively to us. In the nature of things, or in the order of truth, the universal principles are, however, prior to the particulars, and may even be said to be the better known, because it is by knowing them that we explain the particulars. They are cto5ffEt rpOrEpa.
The great forms of reasoning which Aristotle was the first to analyse, induction and syllogism, correspond to this difference be tween prior relatively to us and prior in nature. For in induction (ira-yco-y7)), which is, in fact, syllogistic in form, we proceed from the particulars, and, by collection of instances, advance by means of a ground or reason to a conclusion, while in the syllogism we proceed to our conclusion from premises involving a middle term (,uo-ov), which is the reason for the connection arrived at in the conclusion. In the order of time, induction is a necessary step in the progress of intelligence to that stage in which it can grasp the universal as such, but it is only in and through the process of arly5ftts that the essential character of the universal becomes known. The universal (rd Ka06Xov) is that which can be predicated of a whole class of things (Kara ravros) just because it can be predicated of every member of the class essentially (Ka0' and truly universal judgments, which it is the function of arobEtts to obtain, express this relation.