higher-order predicate calculus

…construed, however, as including also higher-order predicate calculi, which admit variables of higher types, such as those ranging over predicates (or classes and relations) and so on. But then it is a small step to the inclusion of set theory, and, in fact, axiomatic set theory is often regarded as…

A feature shared by LPC and all its extensions so far mentioned is that the only variables that occur in quantifiers are individual variables. It is by virtue of this feature that they are called lower (or first-order) calculi. Various predicate calculi…