1. (logic) a statement that is necessarily true
- the statement `he is brave or he is not brave' is a tautology
2. useless repetition
- to say that something is `adequate enough' is a tautology
Sentences with tautology as a noun:
- It is tautology to say, "Forward Planning".
- The expression "raze to the ground" is a tautology, since the word "raze" includes the notion "to the ground".
- Given a Boolean A, "A OR (NOT A)" is a tautology.
- A logical statement which is neither a tautology nor a contradiction is a contingency.
- A tautology can be verified by constructing a truth tree for its negation: if all of the leaf nodes of such truth tree end in X's, then the original (pre-negated) formula is a tautology.