 For Mach, this was an important acknowledgement of Newton’s insight into the relativity of motion. Starting from Corollary V, the concept of the inertial frame solved the problem of absolute rotation and acceleration, as a problem internal to the system of Newton’s laws. Absolute space could be dispensed with, without undermining Newton’s dynamical distinctions among states of motion. Of course, this point did not dismiss Mach’s skeptical questions regarding the laws themselves. Instead, it posed them in a more precise form: Are Newton’s laws truly general laws of nature, that determine a class of privileged frames? Or do they only describe motions relative to a particular material frame, the fixed stars? Empirical evidence was insufficient to decide. Eventually Mach’s question helped to motivate Einstein’s search for new laws in which privileged frames would not play an essential role. First, however, by comparing Newtonian mechanics with Maxwell’s electrodynamics, Einstein placed the notion of inertial frame on an entirely new footing (see below,  Section 2.2 et seq.). 