 Kant is perfectly well aware of these details from the Scholium to the Principia, but he makes it clear in the Transcendental Aesthetic that he wishes to bracket questions concerning the motion of objects. The reason is that he regards &lt;motion&gt; as an empirical concept, and the Aesthetic aims to articulate a purely a priori conception of space (see A 41/B 58; also MFNS, 4: 482). Instead, Kant tackles physical motion in the Metaphysical Foundations, where he contends that one can distinguish true from relative motion by determining the center of mass frame of the solar system (4: 482, 487, 555–6, 559–63), thereby avoiding the postulation of Newton’s mathematical (absolute) space.