  Du Châtelet indicates what the PSR requires of us as investigators of nature. In the closing sections of her chapter on the nature of body (§162–4), she makes clear that since full knowledge of contingent truths is too complex for humans to grasp through rational intuition (IP §9), we need to turn to some other way of learning them. But because God is bound by the PSR, we cannot appeal directly to his will as the ‘explanation’ of these truths, and so we must turn to proximate causes rather than the ultimate cause for explanation. We must investigate nature in order to try to discern causes of effects—that is, in order to discern the sufficient reason why effects obtain. Empirical observations that we have of how bodies actually do operate in the actual world will lead the investigator to beliefs about features of bodies. These features, however, are not taken to be certainly true as a result of their being supposedly known by introspection into our innate ideas (as they are for Descartes). It may be, therefore, that we are unable to know the sufficient reason for why actuals exist as they do exist, though we surely know that there is a reason, for our experience tells us that actual beings were chosen to exist rather than not to exist.  But God knows the sufficient reason, and it is the reason why he actualized the beings that he did: “Without the principle of sufficient reason, one would no longer be able to say that this universe, whose parts are so interconnected, could only be produced by a supreme wisdom, for if there can be effects without sufficient reason, all might have been produced by accident, that is to say, by nothing” (IP §8, p. 129).