Either A is B or C is D. All cases of A not being B are
cases of C being D.
.'. A being B, C is not D .'. All cases of A being B are
cases of C not being D.
§ 775. The affirmation of the antecedent thus comes under the formula—
All not-A is B,
.'. All A is not-B,
a form of inference which cannot hold except where A and B are known to be incompatible. Who, for instance, would assent to this?—
All non-boating men play cricket.
.'. All boating men are non-cricketers.
§ 776.
Affirmation of Consequent. Simple Conversion of A.
Either A is B or C is D. All cases of A not being B are
cases of C being D.
.'.C being D, A is not B. .'. All cases of C being D are
cases of A not being B.
§ 777. We may however argue in this way—
Conversion of A per accidens.
Either A is B or C is D. All cases of A not being B
are cases of C being D.
.'. C being D, A is sometimes B. .'. Some cases of C being D are
cases of A not being B.