Return to Aristotle, Prior Analytics
Conversion of Necessary Propositions The like also will take place in necessary propositions; for a universal privative is universally converted. But each of affirmative propositions is converted according to a part. For if it is necessary that A should be present with no B, it is also necessary that B should be present with no A; for if it should happen to be present with some A, it would also happen that A would be present with some B. But if A is necessarily present with every, or with some B, B also will necessarily be present with some A; for if it is not necessarily present, neither will A be necessarily present with some B. That, however, which is privative in a part, is not converted, for the reason which has been before assigned. Conversion of Contingent Propositions But with respect to contingent propositions (since that which is contingent is multifariously predicated; for we say that the necessary, the not necessary, and the possible may happen) in all those that are affirmative, there will be a similar mode of conversion. For if A may happen to every, or to some B, B also may happen to some A; for if to no A, neither will A happen to any B. For this has been already demonstrated. In negative propositions, however, the like does not take place; but such things as are said to be contingent, either because they are necessarily not present, or because they are not necessarily present, are converted similarly with the former. For instance, if some one should say it may happen that a man may not be a horse, or that whiteness may be present with no garment. For of these assertions, the first is necessarily not present, and the second is not necessarily present. And the proposition is similarly converted. For if it happens to no man to be a horse, it also happens to no horse to be a man; and if whiteness happens to no garment, a garment also will not happen to any whiteness. For if a garment, necessarily happens to a certain whiteness, whiteness also will necessarily happen to a certain garment; since this was demonstrated before. The like also will take place in a particular negative proposition. But such things as are said to be contingent, because they happen for the most part, and because they are naturally so adapted (after the manner according to which we define the contingent) will not subsist similarly in privative conversions; for a universal privative proposition is not converted, but that which is particular is converted. This, however, will be evident, when we speak of the contingent. But now let thus much be manifest in addition to what has been said, that to happen not to be present with anything, or with something, has an affirmative figure. For “it may happen”, is similarly arranged with “it is”; but “it is” always and entirely produces affirmation in those things to which it is attributed. For instance, “it is” not good, or “it is” not white, or, in short, “it is” not this thing. This, however, will be shown in what follows. But with respect to conversions these will subsist similarly with others.
Return to Aristotle, Prior Analytics
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