 The name ‘compositional(ity)’ first appears in papers of Putnam in 1960 (published 1975) and Katz and Fodor in 1963 on natural language semantics. In talking about compositionality, we have moved to thinking of Tarski’s definition as a semantics, i.e. a way of assigning ‘meanings’ to formulas. (Here we take the meaning of a sentence to be its truth value.) Compositionality means essentially that the meanings assigned to formulas give at least enough information to determine the truth values of sentences containing them. One can ask conversely whether Tarski’s semantics provides only as much information as we need about each formula, in order to reach the truth values of sentences. If the answer is yes, we say that the semantics is fully abstract (for truth). One can show fairly easily, for any of the standard languages of logic, that Tarski’s definition of satisfaction is in fact fully abstract.