(plural De Morgan's laws)
- (mathematics, logic) Either of two laws in formal logic which state that:
- (mathematics) Either of two laws in set theory which state that:
- (mathematics, loosely) Any of various laws similar to De Morgan’s laws for set theory and logic; for example: ¬∀ ⇔ ∃ ¬
Named after its eponym, the British mathematician and logician Augustus De Morgan (1806–1871), who first formulated the laws in formal propositional logic.