 Newton also took issue with Cartesian ideas about motion. His rejection of Cartesian views of space, and his embrace of space as a fundamental concept in philosophy following More’s influence, aligns with his famous discussion of space and time in the Scholium that follows the opening definitions in the Principia. This text influenced nearly every subsequent philosophical discussion of space and time for the next three centuries, so its contours are well known (see DiSalle 2006: ch. 2). In his Principles of Philosophy of 1644, Descartes had distinguished between the “ordinary” and the “proper” view of motion: whereas the ordinary view presents motion as a body’s change of place, the philosopher knows that properly speaking, motion is a body’s change of relations to the bodies that surround it (recall Descartes’s plenum). Newton contends in De Gravitatione that this idea of proper motion, according to which the motion of a body is at least partially a function of its relations to other bodies, is in tension with Descartes’s own laws of nature, also presented in the Principles. For according to the conception of (what we now call) inertia that Descartes presents as his first two laws, a body moving rectilinearly will continue to do so unless caused to deviate from its path—hence a body’s motion is not a function of its spatial relations to other bodies, but rather of its causal relations. That is, according to the first two laws, changing a body’s spatial relations to others bodies will not alter its rectilinear motion unless a causal interaction occurs. This tension runs deep in the Cartesian system. Newton’s Scholium reflects his idea that the concept of motion in the Principia ought to cohere with the laws of motion he endorses. He distinguishes between absolute and relative motion, true and apparent motion, and mathematical and common motion (the same distinctions hold for time, space and place). The former item in each of these three pairings is a concept that coheres with the laws of motion. Newton’s first law reflects Descartes’s laws: it is a new version of the principle of inertia, one incorporating the concept of an impressed force. Since this law indicates that a body’s motion is not a function of its spatial relations to other bodies, but rather of whether forces are impressed on it—which replaces the Cartesian concept of causal interactions that involve only impact (see below)—Newton cannot rely on a body’s motion relative to other bodies if he is to avoid the kind of tension he found in the Cartesian view. Hence he indicates that a body’s true motion—rather than its apparent motion, which depends on our perceptions, or its relative motion, which depends on its spatial relations—is a body’s change of position within space itself. That is, true motion should be understood as absolute motion. This means, in turn, that we must distinguish between the common idea of space, according to which space is conceived of as involving relations among various objects (like the space of our air), and the mathematical idea, one presumably obtained from geometrical reasoning, that space is independent of any objects or their relations. In order to account for the idea that true motion is absolute motion, then, the famous “absolute space” is postulated.