quantification

In logic, specification of quantity or number. There are two main quantifiers: the universal quantifier (‘For all x ...’) and the existential quantifier (‘For at least one/some x ...’). Either of these quantifiers can be defined in terms of the other plus negation – just as ‘some’ can be defined as ‘not all’ in everyday speech.

The quantifier shift fallacy is that of arguing from ‘Every nice girl loves a sailor’ to ‘At least one sailor is loved by every nice girl’. The latter implies, but is not implied by, the former.