The name comes from William Shakespeare, who used tautologies a lot. In other words: Tautologies are true because tautologies are true. Tautology is also used as an important foundational principle in formal logic and philosophy, where it's known as the Law of Noncontradiction : 'A is A, and is not non-A.' The Law itself is an example, since it's a logical axiom, meaning any logical proof of the Law of Noncontradiction would have to depend on the Law of Noncontradiction to be a logical proof. So, many apparent tautologies are worth thinking deeply about, as they often contain surprising insights.
