 Concerning the epistemological status of mechanics, Poincaré positions himself, as in his discussion of geometry, as holding a position between empiricism and a priorism (Poincaré 1902: 111; 2017: 71). The principles of mechanics certainly have, according to Poincaré, an empirical origin, but they nonetheless surpass the bounds of strict empiricism since the experience that leads us to an experimental result rests on the repetition of a phenomenon and therefore requires physical or empirical induction (Poincaré 1902: 26; 2017: 3). Generalizations are either a hypothesis, a law, or a confirmable thesis obtained by the fact that each result of empirical physics can be generalized in different ways. Indeed, we are obligated to simplify the experimental data and the criterion of simplicity is relative to the analytical apparatus we employ, so consequently, simplicity may be only be “apparent.” Such analysis of experimental data may even force us to adjust the experiment. Reflecting on the generalization process shows that it presupposes a belief in the unity and simplicity of nature (Poincaré 1902: 159–165; 2017: 105–108). However, this is only the most general kind of presupposition that is required. The hypothesis of the law of inertia, for example, cannot be obtained except with respect to the preexisting category of the differential equation, which thus replaces the physical induction that leads to a simple experimental fact.