 These themes are apparent already in Cohen’s introduction to Lange (Cohen 1898). Following Hertz, Cohen surveys three different proposals for the principles of mechanics: Newton’s view (which takes as fundamental space, time, mass, and force); an alternative that replaces the notion of force with energy; and Hertz’s own radical view, which uses only the notions of space, time, and mass. Cohen argues for Hertz’s view, emphasizing how it fundamentally reconceptualizes the traditional notion of “mass” (Cohen 1898: 128ff.). This same tendency is even more apparent in Cassirer’s writings on Einstein. He argues that Einstein introduces new a priori principles: the constancy of the speed of light (in the special theory), and the principles of general covariance and the equivalence of inertial and gravitational mass (in the general theory) (1921: 415, 428). And he emphasizes the transformations in the notions of substance, space, and time that the general theory requires (1921: Chs.  3–5).[13]