This is a critical examination of the astonishing progress made in the philosophical study of the properties of the natural numbers from the 1880s to the 1930s. Reassessing the brilliant innovations of Frege, Russell, Wittgenstein, and others, which transformed philosophy as well as our understanding of mathematics, Michael Potter places arithmetic at the interface between experience, language, thought, and the world.

Wittgenstein's philosophical career began in 1911 when he went to Cambridge to work with Russell. He compiled the Notes on Logic two years later as a kind of summary of the work he had done so far. Russell thought that they were 'as good as anything that has ever been done in logic', but he had Wittgenstein himself to explain them to him. Without the benefit of Wittgenstein's explanations, most later scholars have preferred to treat the Notes solely as an interpretative aid in understanding the Tractatus (which draws on them for material), rather than as a philosophical work in their own...