Full Idea
If a well-formed formula of propositional calculus takes the value T for all possible assignments of truth-values to its variables, it is said to be a 'tautology'.
Gist of Idea
A wff is a 'tautology' if all assignments to variables result in the value T
Source
E.J. Lemmon (Beginning Logic [1965], 2.3)
Book Reference
Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.68
Related Idea
Idea 13520 A 'tautology' must include connectives [Wolf,RS]