Principle of Tolerance

The Principle of Tolerance is the methodological doctrine, most closely associated with Rudolf Carnap, that the choice between different linguistic frameworks, logics, or ontologies is not a matter of factual truth but of pragmatic expedience. There is no "correct" language that corresponds to the structure of reality; there are only languages that are more or less useful for formulating scientific theories and solving practical problems. The principle does not license arbitrary choice — within a chosen framework, claims are true or false by the framework's own rules. But the selection of the framework itself is governed by criteria like simplicity, fruitfulness, and expressive power, not by metaphysical correspondence.

Carnap articulated the principle most explicitly in The Logical Syntax of Language (1934) and defended it throughout his career. It represents the mature form of logical positivism: not the elimination of metaphysics by proving it false, but the dissolution of metaphysical pseudo-questions by showing that framework choice is an engineering decision rather than a factual discovery. The principle has direct affinities with contemporary instrumentalist and constructivist philosophies of science, and it anticipates the underdetermination arguments that became central to philosophy of science after Quine's "Two Dogmas of Empiricism."