Universa Philosophia

A consequence is a good deduction of one term from another. Consequence is either formal or material. A formal one is that which follows rightly by reason of the arrangement of the premises, as is clear in all legitimate syllogisms: outside these there is no formal consequence. A material one, however, is when the consequent is true by reason of the matter.

From a superior to an inferior the consequence holds negatively, for example, it is not an animal, therefore it is not a man. But from an inferior to a superior it holds affirmatively, as it is a man, therefore it is an animal. From the opposite of the consequent is inferred the opposite of the antecedent, for example, Peter runs, therefore he moves, the term moves is the consequent, and the term runs is the antecedent: whence it is rightly inferred, he does not move, therefore he does not run. This rule differs in nothing from the prior one, for to move is superior, but to run is inferior. Likewise this rule agrees with the other: from the effect to the cause the consequence holds affirmatively, from the cause to the effect negatively: there is laughter, therefore there is a man; there is no man, therefore there is no laughter.

Here it is customary to object against this rule: it is evidently credible, therefore it is evidently possible: because what is evidently impossible is evidently incredible. On this matter I have treated in the disputation on faith. Now I say briefly that credible is not an antecedent to possible: because they are taken from different headings, for we can believe many impossible things.

When something is inferred from the consequent, it is also inferred from the antecedent, for example, he runs, therefore he moves: if from he moves you infer, therefore he does not rest, you will infer that also from he runs, because what belongs to the inferior belongs also to the superior. But not everything that is inferred from the antecedent belongs to the consequent, as if from he runs you infer, therefore he moves quickly, you will not infer that from he moves: because he can move without moving quickly.

From a false antecedent a true consequent sometimes follows, as Peter is a horse, therefore he is an animal: from a contingent antecedent there can be a necessary consequent, as Peter perceives, therefore he is an animal. But from a true antecedent a false consequent does not follow.