ABSTRACT
Equivalence refers to the two-place sentence operator if p, then q as well as the propositional connective defined by it. The equivalence corresponds to bilateral implication, i.e. both p→q and q→p are valid: Ralph is Philip ‘s father→ Philip is Ralph ‘s son and vice versa. In everyday usage, equivalences correspond to paraphrases like p, if and only if q or p is a necessary and sufficient condition for q, in which case it frequently remains ambiguous as to whether it is a matter of equivalence or of implication. In the framework of lexical semantics ( meaning, semantics) equivalence corresponds to the conventional truth-functional semantic relation of synonymy.
