A will be with every E; and again, if D and H are the same, and E is predicated of H alone, (it may be shown) that A is with no E. Wherefore the inspection must clearly be in this way after the same manner both in the necessary and contingent, for the consideration is the same, and the syllogism both of the contingent and the absolute will be through terms the same in order; in the contingent however we may assume things which are not with, but which may be, for it has been shown that by these a contingent syllogism is produced, and the reasoning is similar in the case of the other predications. From what has been said then it appears not only that it is allowable for all syllogisms to be formed in this, but that they cannot be formed in any other way, for every syllogism has been shown to originate through some one of the before-named figures, and these may not be constituted through any other than the consequents and antecedents of a thing, for from these are the premises and assumption of the middle, so that it is not admissible that a syllogism should be produced through other things.
Chapter 30
The way then of proceeding in all (problems), both in philosophy and in every art and discipline, is the same, for we must collect about each of them those things which are with, and the subjects which they are with, and be provided with as many as possible of these, considering them also through three terms in one way subverting, but in another constructing according to truth (we reason) from those which are truly described to be inherent, but as regards dialectic syllogisms (we must reason) from probable propositions. Now the principles of universal syllogisms have been mentioned, how they subsist, and how we must investigate them, that we may not direct our attention to every thing which is said, nor to constructing and subverting the same things, nor both constructing universally or particularly, nor subverting wholly or partially, but look to things fewer and definite; as to each however we must make a selection, as of good or of science. The peculiar principles indeed in every science are many,
