gism, for every syllogism is either de inesse, or of that which exists necessarily or contingently, but that this is neither de inesse, nor of that which necessarily exists, is clear, since the affirmative is subverted by the negative, and the negative by the affirmative, wherefore it remains that it is of the contingent, but this is impossible, for it has been shown that when the terms are thus, the first is necessarily inherent in all the last, and contingently is present with none, so that there cannot be a syllogism of the contingent, for the necessary is not contingent. Thus it is evident that when universal terms are assumed in contingent propositions, there arises always a syllogism in the first figure, both when they are affirmative and negative, except that being affirmative it is complete, but if negative incomplete, we must nevertheless assume the contingent not in necessary propositions, but according to the before-named definition, and sometimes a thing of this kind escapes notice.
Chapter 15
If one proposition be assumed to exist, but the other to be contingent, when that which contains the major extreme signifies the contingent, all the syllogisms will be perfect and of the contingent, according to the above definition. But when the minor (is contingent) tney will all be imperfect, and the negative syllogisms will not be of the contingent, according to the definition, but of that which is necessarily present with no one or not with every; for if it is necessarily present with no one, or not with every, we say that "it happens" to be present with no one and not with every. Now let A be contingent to every B, and let B be assumed to be present with every C, since then C is (included) under B, and A is contingent to every B, A is also clearly contingent to every C, and there is a perfect syllogism. So also if the proposition A B is negative, but B C affirmative, and A B is assumed as contingent, but B C to be present with (simply), there will be a perfect syllogism, so that A will happen to be present with no C.
