Book 1
2.14
But since few of the propositions of the rhetorical syllogism are necessary, for most of the things which we judge and examine can be other than they are, human actions, which are the subject of our deliberation and examination, being all of such a character and, generally speaking, none of them necessary; since, further, facts which only generally happen or are merely possible can only be demonstrated by other facts of the same kind, and necessary facts by necessary propositions (and that this is so is clear from the AnalyticsAristot. APr. 1.8.13.), it is evident that the materials from which enthymemes are derived will be sometimes necessary, but for the most part only generally true; and these materials being probabilities and signs, it follows that these two elements must correspond to these two kinds of propositions, each to each.That is, probabilities and signs correspond to general and necessary propositions. This is not strictly correct; only the τεκμήρια correspond to the necessary propositions, the other signs and the other probabilities to the general or contingent propositions.
2.15
For that which is probable is that which generally happens, not however unreservedly, as some define it, but that which is concerned with things that may be other than they are, being so related to that in regard to which it is probable as the universal to the particular.