 It was implicit in Frege that each of the endlessly many sentences of an ideal language would have a compositionally determined truth-condition. Frege did not actually specify an algorithm that would associate each sentence of his Begriffsschrift with its truth-condition. But  Tarski (1933) showed how to do this for the  first-order predicate calculus, focussing on interesting cases of  multiple quantification like the one shown below: