Logical equivalence

• In logic, statements p and q are logically equivalent if they have the same logical content

• (Mendelson 1979:56) two statements are equivalent if they have the same truth value in every model

Symbol is ≡ or Û

Logical Equivalence Table

DeMorgan’s Law

• Probably the most important logical equivalence

n ¬(p Ù q) ≡ ¬p Ú ¬q

n ¬(p Ú q) ≡ ¬p Ù ¬q