 Poincaré’s philosophy is primarily that of a scientist originating in his own daily practice of science and in the scientific debates of his time. As such, it is strongly influenced by the reflections of Ernst Mach, James Maxwell and Hermann von Helmholtz. However, his thinking is also strongly influenced by the philosophical doctrines of his time (those of Emile Boutroux, who was his brother-in-law, but also of Jules Lachelier, William James, etc.), and is imbued with the neokantism that was very much in vogue. Nevertheless, one must not assume that Poincaré’s “Kantian” vocabulary is exactly that of the German philosopher, given that Poincaré often radically changes the meaning of Kant’s terms.