This chapter argues for the centrality of Neurath's syntacticism to his physicalism, encyclopedism, and the unity of science program. I defend the intelligibility of Neurath's opposition to semantics and underline the role syntacticism plays in his anti-metaphysical empiricism. I argue that Neurath was correct to fear that the semantic turn would spell the end of logical empiricism. Many of the most influential metaphysical arguments of the twentieth century turn on premises that would be undermined by a Neurathian rejection of semantics.