contrapositive

There is an apparent exception to this when the real Middle in an argument is a contrapositive term, not-M.

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

For a Disjunctive in I., of course, there is no Contrapositive.

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