The aim of this paper is to present Duhem’s critical view of the dynamical development of mechanics according to two principles of his theory of the development of physics: the continuous and the rational development of physics. These two principles impose a formal conception of physics that aims at demarcating physics from the metaphysical view on the one hand and the pragmatist/conventionalist view on the other hand. Duhem pursues an intermediary conception of physics, a representational system of empirical laws based upon formal principles. This formal conception of physics will adjust to his idea of scientific progress in the form of a sequence of representational systems as structures of increasing comprehensiveness of empirical laws, which leads him to defend a convergent structural realism pointing to an ideal physical theory.