  Tarski’s truth-definition is one of the most debated contemporary philosophical and logical ideas. It strongly influenced semantics, philosophy of language, philosophy of science and epistemology. In particular, it became the first step toward model-theory, a central branch of mathematical logic. Two applications of this definition are worth mentioning. Firstly, Tarski succeeded in formulating an exact definition of “logical consequence” (“following from” or “logical entailment”):