  Carnap holds that the role of philosophy is to analyze and clarify the language of science, and to formulate and recommend alternative languages. After 1932, he holds that there are languages which differ in expressive power, not merely as notational variants. The difference between intuitionistic logic and classical logic is an important example here, as is the difference between the language of Newtonian mechanics and the language of relativistic mechanics. (Earlier, he says, he had ‘overlooked the fact that there is a multiplicity of possible languages’, Carnap 1934, 245; cf. also 322 of the same work.) Within a given language, there may be only one correct theory on a given subject. But the choice of a language is in that respect unlike the choice of a theory. In deciding which theory is correct, we will appeal to observations but also to the rules of the language; no such appeal is possible when we are choosing a language, for in this case it is the rules themselves that we are choosing. So Carnap holds that there is no one correct language. This idea has become known as the Principle of Tolerance; from the 1930s on, it is fundamental to Carnap’s view of what philosophy is and how it differs from science. (That there is such a difference is a point which Carnap never questions.) Because there is no one correct language, it is no part of the philosopher’s job to prescribe this or that language, merely to analyze, to clarify, and to suggest alternatives.