 At the same time, we can say that the concept of inertial frame retains at least one aspect of the relevance that it had for Newton. As we saw, Newton was aware that he could not determine (to put it in our language) an actual inertial frame from his analysis of the solar system; Corollary VI implied that all local phenomena were compatible with an acceleration of the entire system, by nearly equal and nearly parallel accelerative forces acting on the sun, the planets, and their satellites. By the very same reasoning, however, he established that such a uniformly accelerating frame was sufficient for a successful analysis of the relevant causes acting within the system—those causes that determine the system’s configuration. From this analysis he could determine the configuration of the system, that is, determine that our system is approximately Keplerian, with small deviations from Keplerian motion accounted for by perturbative actions of the members of the system on each other. In other words, though a true inertial frame cannot be determined, a sufficient approximation to an inertial frame provides a sufficient basis for this causal account. 