High Quality Content by WIKIPEDIA articles! Predicate transformer semantics was introduced by Dijkstra in his seminal paper "Guarded commands, nondeterminacy and formal derivation of programs". They define the semantics of an imperative programming language by assigning to each statement in this language a corresponding predicate transformer: a total function between two predicates on the state space of the statement. In this sense, predicate transformer semantics are a kind of denotational semantics. Actually, in Guarded commands, Dijkstra uses only one kind of predicate transformers: the well-known weakest preconditions Moreover, predicate transformer semantics are a reformulation of Floyd-Hoare logic. Whereas Hoare logic is presented as a deductive system, predicate transformer semantics (either by weakest-preconditions or by strongest-postconditions) are complete strategies to build valid deductions of Hoare logic.