were granted, it is absolutely necessary for us also to withdraw from what we granted, and from accepting what does not follow from the words in which our concessions were made. For the inference is now not our inference, nor does it result with our assent, since we have withdrawn from the premises which we granted. We ought then both to examine such kinds of premises, and such change and variation of them (from one meaning to another), by which in the course of questioning or answering, or in making the syllogistic conclusion, or in any other such way, the premises undergo variations, and give occasion to the foolish to be confounded, if they do not see what conclusions (consequences) are. For what reason ought we to examine? In order that we may not in this matter be employed in an improper manner nor in a confused way.
And the same in hypotheses and hypothetical arguments; for it is necessary sometimes to demand the granting of some hypothesis as a kind of passage to the argument which follows. Must we then allow every hypothesis that is proposed, or not allow every one? And if not every one, which should we allow? And if a man has allowed an hypothesis, must he in every case abide by allowing it? or must he sometimes withdraw from it, but admit the consequences and not admit contradictions? Yes; but suppose that a man says, If you admit the hypothesis of a possibility, I will draw you to an impossibility. With such a person shall a man of sense refuse to enter into a contest, and avoid discussion and conversation with him? But what other man than the man of sense can use argumentation and is skilful in questioning and answering, and
B, every B is also A, he might answer that it is. But if you put the conversion in this material form: "Every goose is an animal," he immediately perceives that he cannot say, "Every animal is a goose." What does this show? It shows that the man's comprehension of the proposition, every A is B, was not true, and that he took it to mean Something different from what the person intended who put the question. He understood that A and B were coextensive. Whether we call this reasoning or something else, makes no matter. A man whose understanding is sound cannot in the nature of things reason wrong; but his understanding of the matter on which he reasons may be wrong somewhere, and he may not be able to discover where. A man who has been trained in the logical art may show him that his conclusion is just according to his understanding of the terms and the propositions employed, but yet it is not true.
