This chapter discusses how Carnap’s philosophy of language affects his position on language planning issues. Carnap was an Esperantist from an early age, and he kept his interest for international auxiliary languages active throughout his life. In his Intellectual Autobiography, he clearly mentions the relation between his activity of building symbol systems as a logician and his interest for language planning for international communication. His controversy with Wittgenstein regarding Esperanto illustrates two opposing views of language, one as a functional device for various purposes and one as a carrier of tradition and identity. Carnap’s dismissal of the latter is rooted both in his principle of tolerance (and its underlying instrumentalism) and in logical empiricism’s attack on metaphysical concepts such as Volksgeist, shared by other language planners who emphasized the instrumental purpose of language and supported locutors’ active intervention in it either by language reform or by language construction. We argue that the antimetaphysical rejection of the romanticist view of language, sustained by Vienna Circle, led to a more liberal and flexible attitude toward language planning issues. Finally, the internationalism of logical empiricists was effective in shaping their favourable disposition towards international auxiliary languages.

With a view to highlighting the importance of archival and less well-known primary sources for our understanding of Rudolf Carnap’s philosophy, this chapter investigates several examples of concrete influences on his thinking, from nineteenth-century Herbartianism and empiriocriticism, the German Youth Movement, Bauhaus modernism and the revolution from the right, toward the Vienna Circle and post-WWII analytic philosophy. These examples demonstrate that Carnap’s philosophy had always been shaped by practical motives; he developed a philosophical stance that is directed at the reality of life and integrates cognitive as well as non-cognitive elements. This meta-philosophical view that carefully investigates the borders between the scientifically comprehensible (viz., the cognitive) and those aspects of reasoning that merely comprise personal attitudes (viz. the noncognitive) developed through various stages, from the "scientific world-conception" and antimetaphysics of the Vienna Circle toward Carnap’s mature views on inductive logic and human decision-making. The upshot is that noncognitivism as being understood by Carnap and his philosophical allies rather than denouncing value statements as arbitrary and irrational embeds them into a rational scientific discourse, to maximize rationality in connection with moral and political decision making.