Convention or principle laid down by Tarski as a ‘material adequacy condition’ governing the enterprise of giving a definition of the truth-predicate for a language. A theory satisfies the requirement only if every instance of the schema ‘S is true if and only if p’ is derivable within it. Here S is a description of a sentence of the object language, and p is its translation into the metalanguage. The leading idea is that our characterization of the language will be incomplete unless we can derive such a biconditional for any sentence that the object language can frame. If we were left unable to say under what conditions some sentence would be true, we would not have a full account of the ways the object language can put together sentences. Tarski expresses this by saying that we would not have an adequate definition of the truth-predicate for the language. He believed that because of the semantic paradoxes no language can define its own truth-predicate. To fully describe the semantics of a language therefore means ascending to a higher language, or metalanguage, containing terms not expressible in the original language on pain of contradiction. Convention T became centrally important to philosophers working on Davidson's programme of giving a semantically sound description of natural languages. It remains controversial just how legitimate this appropriation of Tarski's ideas is: the shift in focus that has worried certain philosophers is sometimes put by saying that whereas Tarski took translation for granted, and sought to understand truth, Davidson takes truth for granted, and seeks to understand translation.