Arguments Containing Partitive Propositions.
(5) All that glitters is not gold,
Tinsel glitters,
∴ Tinsel is not gold.
The quantity sign “all” when used with “not” is ambiguous; it may mean “no” or “some-not.” The only way to determine which meaning is intended is to try boththese quantity signs, selecting the one which seems to fit best the author’s meaning. When “all-not” means “some-not” the proposition which it introduces is called a partitive proposition; since such always suggests a complementary proposition. (See [page 133].) For example, “Some glittering things are not gold,” suggests its complement, “Some glittering things are gold.” In testing the foregoing argument it is clear that “All that glitters is not gold” does not mean “No glittering thing is gold,” so much as it implies “Some glittering things are not gold.” Thus the argument takes this form:
O Some M
glittering things are not G
gold,
A S
Tinsel M
glitters,
E ∴ S
Tinsel is not G
gold.
The mood is
