Predicate logic (also known as first-order logic or precdiate caculus) allows logical formulae including variables (such as X, Y, Person, Parent) and predicates (such as is_child_of(Person, Parent). It does not allow higher-order formulae, that is predicte symbols cannot also be used as variables.
Used on Chap. 2: pages 21, 22; Chap. 5: page 90
Also known as predicate calculus