  Clarke's rejection of any “similitude” between the movements of a balance and the acts of an agent is closely connected to his disagreement with Leibniz over PSR. In his response to the second letter Clarke appears to accept PSR. Thus he says: “It is very true, that nothing is, without a sufficient reason why it is, and why it is thus rather than otherwise” (L-C, 20). Clearly, if when writing “nothing is” Clarke means to include any fact or truth whatever, then he cannot consistently go on, as he does, to exempt certain facts or truths from the necessity of having a sufficient reason. Leibniz may have read Clarke's “nothing is” as encompassing any fact or truth whatever, which would approach Leibniz's own understanding of PSR. If so, this would explain why in his third letter Leibniz complains that although Clarke grants him this important principle, “he grants it only in words, and in reality denies it. Which shows that he does not fully perceive the strength of it” (L-C, 25). However, despite his statement “nothing is without a sufficient reason why it is,” it is clear that Clarke cannot have intended to agree with Leibniz that every fact or truth has a sufficient reason. Nor could he have agreed that every contingent fact or truth has a sufficient reason. For he immediately goes on to say that “this sufficient reason is oft-times no other, than the mere will of God,” citing as an example God's volition to create this system of matter in one particular place within absolute space, rather than in some other place in absolute space. There is simply nothing to recommend one particular place in absolute space over another. Hence, in this case there can be no other reason than the mere will of God. (Presumably, Clarke would say that God had a sufficient reason to create this system of matter in some place or other in absolute space, but He did not have a sufficient reason to create it in this particular place.) In his third letter Leibniz cites this case as just the sort of thing that PSR rules out as impossible. On his understanding of PSR there can be no situations at all in which a choice has been made without a sufficient reason for making that particular choice. To think otherwise is to suppose an exception to PSR. (Leibniz does allow that there are many human acts that appear to lack a sufficient reason. There are acts for which we cannot find a sufficient motive. For example, no motive is apparent for why an agent stepped over the threshold with his left foot rather than his right. But he supposed in all such cases there is some unconscious perception or passion that provides the sufficient reason.) It is clear that Clarke allows for such exceptions.