 Cohen never gave up the view that the concepts of the infinite, infinitesimals, and continuity were central to a philosophical account of pure thinking and knowledge. Yet his account of those mathematical concepts was never convincing to mathematicians and philosophers of mathematics in the analytic tradition. Gottlob Frege complained that Cohen’s views in the Principle of the Infinitesimal Method were too unclear to be intelligible (Frege 1885 [1984]). Bertrand Russell objected that Cohen failed to understand that mathematicians now had a formal treatment of continuity and limits that freed them of any commitment to infinitesimals (Russell 1903, Ch. 41). Even Cassirer, Cohen’s own student, abandoned Cohen’s account of infinitesimals, likely in response to Russell’s objections. Consequently, Cassirer also abandoned many of the details of Cohen’s theory of knowledge in the Logic. (See Giovanelli 2016 for an account of how even Cohen’s allies were unpersuaded by Cohen’s account of the infinitesimal concept and its centrality to his account of knowledge. Edgar forthcoming argues that Russell in particular failed to understand the philosophical significance of Cohen’s account of the infinitesimal concept and its place in his theory of knowledge.)