The Obverse, Converse, and Contrapositive, of Hypotheticals (admitting the distinction of quality) may be exhibited thus:
| Datum. | Obverse. |
| A. If A is B, C is D | If A is B, C is not d |
| I. Sometimes when A is B, C is D | Sometimes when A is B, C is not d |
| E. If A is B, C is not D | If A is B, C is d |
| O. Sometimes when A is B, C is not D | Sometimes when A is B, C is d |
| Converse. | Contrapositive. |
| Sometimes when C is D, A is B | If C is d, A is not B |
| Sometimes when C is D, A is B | (none) |
| If C is D, A is not B | Sometimes when C is d, A is B |
| (none) | Sometimes when C is d, A is B |
As to Disjunctives, the attempt to put them through these different forms immediately destroys their disjunctive character. Still, given any proposition in the form A is either B or C, we can state the propositions that give the sense of obversion, conversion, etc., thus:
Datum.—A is either B or C;
Obverse.—A is not both b and c;
Converse.—Something, either B or C, is A;
Contrapositive.—Nothing that is both b and c is A.
For a Disjunctive in I., of course, there is no Contrapositive. Given a Disjunctive in the form Either A is B or C is D, we may write for its Obverse—In no case is A b, and C at the same time d. But no Converse or Contrapositive of such a Disjunctive can be obtained, except by first casting it into the hypothetical or categorical form.
The reader who wishes to pursue this subject further, will find it elaborately treated in Dr. Keynes' Formal Logic, Part II.; to which work the above chapter is indebted.