 Poincaré’s views brought him into collision with Bertrand Russell in the 1890s when he was emerging from his brief Hegelian phase and entering his Kantian phase. Russell was trying to establish the Kantian a priori by arguing that there is one fundamental geometry, which is projective geometry, and we have synthetic a priori knowledge of it (see Griffin 1991 on Russell and Nabonnand 2000 on the controversy).