From Foundations of Logic and Mathematics (1939) (and Introduction to Semantics, 1942) Carnap had taken up Tarski’s conception of semantic truth. The principle of tolerance in the Logical Syntax remained intact, but in the following refined form: the syntactic rules of formation can be chosen freely; if the syntactical rules of transformation (derivation, inference) are determined prior to the semantic rules, they may be determined freely as well, but the semantic rules will have to be selected