 Newton now realized, in short, that the dispute between the heliocentric and geocentric views of the universe had been mistakenly framed. The proper question about “the system of the world” was not “which body is at rest in the center?” but “where is the center of gravity of the system, and which body is closest to it?” For in a system of orbiting bodies, only their common center of gravity will be unaccelerated, and by “Law 3”, the motions of the bodies in the system will be the same, whether its center of gravity is at rest or in uniform rectilinear motion. By explicitly asserting the dynamical equivalence of “whole spaces” that may moving uniformly or at rest, Newton made it clear that the solution to the problem of “the system of the world” is the same with respect to any such moving space as it is with respect to immobile space. Thus he came as close to articulating the concept of the inertial frame as anyone before the late 19th century.