be present with some B, B must also necessarily be present with some A, for if it were present with none, neither would A be present with any B, but if A is not present with some B, B need not be present with some A, for example, if B is "animal," but A, "man," for man is not present with "every animal," but "animal" is present with "every man."
Chapter 3
The same system will hold good in necessary propositions, for an universal negative is universally convertible, but either affirmative proposition particularly; 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 any, A also might happen to be present with some B. But if A is of necessity present with every or with some certain B, B is also necessarily present with some certain A; for if it were not necessarily, neither would A of necessity be present with some certain B: a particular negative however is not converted, for the reason we have before assigned.
In contingent propositions, (since contingency is multifariously predicated, for we call the necessary, and the not necessary, and the possible, contingent,) in all affirmatives, conversion will occur in a similar manner, for if A is contingent to every or to some certain B, B may also be contingent to some A; for if it were to none, neither would A be to any B, for this has been shown before. The like however does not occur in negative propositions, but such things as are called contingent either from their being necessarily not present, or from their being not necessarily present, (are converted) similarly (with the
