§ 517. This will be found to resolve itself on analysis into three steps of inference in the following order—
(1) Permutation.
(2) Simple Conversion.
(3) Permutation.
§ 518. Let us verify this statement by performing the three steps.
All A is B.
.'. No A is not-B (by permutation).
.'. No not-B is A (by simple conversion).
.'. All not-B is not-A (by permutation).
All Englishmen are Aryans.
.'. No Englishmen are non-Aryans.
.'. No non-Aryans are Englishmen.
.'. All non-Aryans are non-Englishmen.
§ 519. Conversion by contraposition may be complicated in appearance by the occurrence of a negative term in the subject or predicate or both, e.g.
All not-A is B.
.'. All not-B is A.
Again,