Return to Aristotle, Prior Analytics
Every proposition is either of that which is simply present, or of that which is present from necessity, or of that which may be present((i.e., Possible, or Contingent)); and of these, some are affirmative but others negative, according to each appellation, and again, since of affirmative and negative propositions, some are universal, others partial, and others indefinite. This being the case, it is necessary that the universal negative proposition of that which is present may be converted in its terms. Thus, for instance, if no pleasure is good, neither will any good be pleasure. But it is necessary that a universal affirmative (categoric) proposition should be converted indeed, yet not universally, but in a part. For instance, if all pleasure is good, it is also necessary that a certain good should be pleasure. And of particular propositions it is necessary that the particular affirmative should be converted in a part; for if a certain pleasure is good, a certain good will also be pleasure. But it is not necessary that a particular negative proposition should be converted. For it does not follow that if man is not present with a certain animal, that animal also is not present with a certain man. Let the proposition A B, therefore, be the first privative universal. Hence, if A is present with no B, neither will B be present with any A. For if it should be present with some A, as, for instance, with C, it will not be true that A is present with no B; since C is something of B. But, if A is present with every B, B will be present with some A. For if with no A, neither will A be present with any B; but it was supposed to be present with every B. Conversion also is in a similar manner produced, if the proposition is particular. For if A is present with some B, it is also necessary that B should be present with some A. For if it is present with no A, neither will A be present with any B. But if A is not present with some B, it is not necessary that B also should not be present with A. For instance, if B is animal, but A man; man, indeed, is not present with every animal, (i.e. is not participated by every animal), but animal is present with every man.
Return to Aristotle, Prior Analytics
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