As Neurath fended off Kallen's attacks in the last year of his life, he was also immersed in a long and frustrating debate with Carnap. It began in 1942 with a renewed skirmish over the viability of semantics and Tarski's theory of truth. By 1944, it had become exacerbated by a dispute over Neurath's encyclopedia monograph, Foundations of Social Science (Neurath 1944). As we see below in this chapter, Neurath charged Carnap and semantics with metaphysical mischief that had potentially severe political consequences. In some ways, Neurath's complaints against semantics paralleled Kallen's complaints about the Unity of Science movement, and they tended to the same overall historical effect: They helped to widen and sustain a rift within the movement that would later help facilitate logical empiricism's subsequent break with the Unity of Science movement. The debate arrayed Neurath, Frank, and Morris, on the one side, against most other logical empiricists whom Neurath and Frank believed were veering into formal, logical modes of philosophical inquiry that, were they to become dominant, would reduce the practical utility and relevance of philosophy of science.

Carnap and Neurath

Histories of the Vienna Circle usually adopt the view that the circle was intellectually and politically divided into a more radical left, led by Neurath, Carnap, and Hahn (who together wrote the circle's manifesto), and a more conservative right, led by Schlick and Friedrich Waismann.