Tautology

Tautology may refer to:

• Tautology (rhetoric), using different words to say the same thing, or a series of self-reinforcing statements that cannot be disproved because they depend on the assumption that they are already correct
• Tautology (logic), a technical notion in formal logic, universal unconditioned truth, always valid
• Tautology (rule of inference), a rule of replacement for logical expressions in some systems of propositional logic