A similar thing happened with the principle of obversion.    From Wordnik.com.  [The Traditional Square of Opposition] Reference

These are the theory of the syllogism and the doctrines of contraposition and obversion.    From Wordnik.com.  [The Traditional Square of Opposition] Reference

Take any universal affirmative proposition; convert it by obversion.    From Wordnik.com.  [Logic Deductive and Inductive] Reference

Thus, by obversion, each of the four propositions retains its quantity but changes its quality: A. to E.    From Wordnik.com.  [Logic Deductive and Inductive] Reference

Contraposition needs no justification by the Laws of Thought, as it is nothing but a compounding of conversion with obversion, both of which processes have already been justified.    From Wordnik.com.  [Logic Deductive and Inductive] Reference

Again, having obtained the obverse of a given proposition, it may be desirable to recover the obvertend; or it may at any time be requisite to change a given infinite proposition into the corresponding direct affirmative or negative; and in such cases the process is still obversion.    From Wordnik.com.  [Logic Deductive and Inductive] Reference

By obversion.    From Wordnik.com.  [The Traditional Square of Opposition] Reference