(E) If A is B, C is never D = No cases of A being B are cases of C
being D. (No AB is a CD.)
(I) If A is B, C is sometimes D = Some cases of A being B are cases
of C being D. (Some AB's are CD's.)
(O) If A is B, C is sometimes not D = Some cases of A being B are
not cases of C being D. (Some AB's are not CD's.)
§ 706. Or, to take concrete examples,
(A) If kings are ambitious, their subjects always suffer.
= All cases of ambitious kings are cases of subjects suffering.
(E) If the wind is in the south, the river never freezes.
= No cases of wind in the south are cases of the river freezing.
(I) If a man plays recklessly, the luck sometimes goes against him.
= Some cases of reckless playing are cases of going against one.
(O) If a novel has merit, the public sometimes do not buy it.
= Some cases of novels with merit are not cases of the public buying.
§ 707. We have seen already that the disjunctive differs from the conjunctive proposition in this, that in the conjunctive the truth of the antecedent involves the truth of the consequent, whereas in the disjunctive the falsity of the antecedent involves the truth of the consequent. The disjunctive proposition therefore
Either A is B or C is D