(1) Permutation.
(2) Simple Conversion.
(A) All A is B.
.'. No A is not-B (by permutation).
.'. No not-B is A (by simple conversion).
(O) Some A is not B.
.'. Some A is not-B (by permutation).
.'. Some not-B is A (by simple conversion).
§ 507. The term conversion by negation has been arbitrarily limited to the exact inferential procedure of permutation followed by simple conversion. Hence it necessarily applies only to A and 0 propositions, since these when permuted become E and 1, which admit of simple conversion; whereas E and 1 themselves are permuted into A and 0, which do not. There seems to be no good reason, however, why the term 'conversion by negation' should be thus restricted in its meaning; instead of being extended to the combination of permutation with conversion, no matter in what order the two processes may be performed. If this is not done, inferences quite as legitimate as those which pass under the title of conversion by negation are left without a name.
§ 508. From E and 1 inferences may be elicited as follows—
(E) No A is B.
.'. All B is not-A (A).
(I) Some A is B.
.'. Some B is not not-A (O).
(E) No good actions are unbecoming.
.'. All unbecoming actions are not-good (A).
(I) Some poetical persons are logicians.
.'. Some logicians are not unpoetical (O).