Logicism, as developed by Frege and Russell, is the thesis that pure mathematics is part of logic. While the logicist thesis was a central doctrine in the philosophy of mathematics of the late nineteenth and early twentieth century, it did not present a uniform research project. Different scholars used the term “logicism” to describe different practices of reducing mathematical theories to higher-order logic or set theory.2 This holds true, in particular, of work by philosophers related to modern empiricism. Logicism presents one of the cornerstones of logical empiricism.3 At the same time, the views defended by Carnap, Hahn, and Hempel (among others) differ significantly from Frege’s and Russell’s original thesis.