 Tarski’s work (1930a, 1930b, 1935, 1936) on the methodology of the deductive sciences of the 1920s and 1930s studies the axiomatic method abstractly and introduces for the first time the abstract concept of consequence operation. Tarski had mainly in mind the different mathematical axiomatic theories. On these theories, the sentences that are proved from the axioms are consequences of them but (of course) almost all of them are not logical truths; under a suitable formalization of these theories, a logical calculus like Frege’s or Russell’s can be used to derive the consequences of the axioms. Tarski set the framework to study the most general properties of the operation that assigns to a set of axioms its consequences.