Tautology



A tautology is a statement that is true by virtue of its logical form, rather than by the substance of the statement. As a result, the statement itself is meaningless. Tautology is the opposite of contradiction.

Examples of tautologies include:
 * "Either it will rain tomorrow, or it will not rain."
 * "Be yourself."
 * "It is wrong to do bad things."

In argument, the correct response to a tautology is not, "You're wrong," but rather, "That doesn't mean anything."

Stating a tautology can be useful under some circumstances -- especially when it is necessary to prove the validity of the truth shown by the tautology. In this case, the tautology may be better called a "logical necessity" or axiom.

For example, Aristotle wrote in defense of the law of identity (A=A): Now 'why a thing is itself' is a meaningless inquiry (for -- to give meaning to the question 'why' -- the fact or the existence of the thing must already be evident - e.g. that the moon is eclipsed - but the fact that a thing is itself is the single reason and the single cause to be given in answer to all such questions as why the man is man, or the musician musical', unless one were to answer 'because each thing is inseparable from itself, and its being one just meant this' this, however, is common to all things and is a short and easy way with the question). (Metaphysics VII, 17.)

The term "Natural selection" embeds a tautology - if something happens in nature, that selection of events fits the term. Phrased as the "survival of the fittest", it reduces to the survival of the survivors or the fitness of the fit. The terms may be freely applied to any natural phenomenon.