Terminology Tuesday: Tautology

A tautology is a contentless statement; something true by definition and uninformative of the real world. “All bachelors are unmarried men” is a tautology, as is “All triangles have three sides.” Neither statement informs us that the subject exists. They only mean, “If X exists, then it is X.” If there are any bachelors in the universe, they are unmarried. The tautology does not tell us that a bachelor really exists. David Hume called this kind of statement the “relation of ideas.” Immanuel Kant called them “analytic.”

Tautologies and Empirical Statements. Tautologies are usually contrasted with empirical statements that have content: “The tree outside my window is an oak.” “The car in my yard is black.” While empirical statements have content, they are not logically necessary. That is, they may be false. Tautologies, on the other hand, are logically necessary, since they are true by definition. They do not say a thing, but they are necessarily true. An analytic statement is simply expletive because the predicate explains the idea present in the subject. Unlike empirical statements, analytic statements are not ampliative. The predicate doesn’t add to what is known from the subject. “The house is brown” is ampliative, since the predicate amplifies on the subject. We learn the color of the house, which we would not have known simply from examining the concept “house.”

While all tautologies are absolutely certain, not everything that is absolutely certain is a tautology. “I exist.” is certain. I cannot deny it unless I actually exist to deny it. Likewise the assertion about my existence, “I am I” is not a mere tautology, since it asserts something about existence. Also, “Being exists” is not an empty statement, since it affirms existence (see FIRST PRINCIPLES; METAPHYSICS; REALISM).

While tautologies or statements true by definition are empty in themselves, they can be filled with content and used to prove something is true. The statement, “If this is an effect, it must have a cause” is an empty statement. But once it is combined with a statement about the real world, such as “The existing world is an effect,” then it can be used to assert that the world has a Cause (see GOD, EVIDENCE FOR). So simply because a statement is analytic (true by definition) does not mean it cannot be used to demonstrate something about the real world.

Geisler, N. L. (1999). Tautology. In Baker encyclopedia of Christian apologetics (p. 714). Grand Rapids, MI: Baker Books.