contrapositive

In the case of the I proposition the contrapositive is impossible, as infringing the main rule of conversion.

Every positive in thought has a contrapositive, and the positive and contrapositive are of the same kind.

But take the obverse of the contrapositive of both premises: All m is p; All m is s: ∴ Some s is p.

We will show in this manner that the above is really the contrapositive of the 0 proposition.

Every impression felt is felt as a change or transition from something else: but it is a variation of the same impression—the something else, the contrapositive, is not entirely different.