If, then, with regard to any of them we are well supplied with matter for a discussion, we shall secure a preliminary admission that however it is in these cases, so it is also in the case before us; then when we have proved the former we shall have proved, on the strength of the hypothesis, the matter before us as well; for we have first made the hypothesis that however it is in these cases, so it is also in the case before us, and have then produced the demonstration.