This chapter examines the increasing use of mathematics in Arthur Cecil Pigou's economic writings. Pigou's attitudes towards biological and mechanical analogies as means by which to capture economic reality are considered by examining his attitudes to method generally and by reconstructing aspects of his training in mathematics and his use of mathematics over the course of his career. It is argued that Pigou's heightened use of mathematics was a continuous and considered departure from Alfred Marshall's practice of relegating mathematical analysis to footnotes and appendices. It is also demonstrated, however, that Pigou retained the Marshallian trait of employing a plurality of methods, and that this can be understood in terms of the Fleckian notion of evolving thought styles. Pigou's book The Theory of Unemployment is used as a case study to underline arguments presented in the chapter.