Proposition Equivalences

Two proposition are equivalent if they always have same truth value.

Tautologies, Contradictions, Contingencies

• tautology
  • a proposition which is always true.
  • e.g. $p\vee \neg p$
• contradiction
  • a proposition which is always false.
  • e.g. $p\wedge \neg p$
• contigency
  • which is neither tautology nor contradiction
  • e.g. $p$

Logical Equivalent