  An important issue in the Leibniz-Clarke correspondence concerns the Principle of Sufficient Reason (PSR), particularly its implications for how we must understand divine and human freedom. In his second letter Leibniz advances the principle and pronounces on its implications for theology and metaphysics. “Now, by that single principle, viz.  that there ought to be a sufficient reason why things should be so, and not otherwise, one may demonstrate the being of a God, and all the other parts of metaphysics or natural theology” (L-C, 16).  Leibniz elsewhere expresses PSR more fully as the principle “…that no fact can be real or existent, no statement true, unless there be a sufficient reason why it is so and not otherwise,…” (1714, paragraph 32). He illustrates PSR by citing the example of Archimedes who observed that if there be a perfect balance, and if equal weights are hung on the two ends of that balance, the balance will not move. Why? Leibniz answers: “It is because no reason can be given, why one side should weigh down, rather than another” (L-C, 16). It was perhaps unfortunate for Leibniz to use this example. For it enabled Clarke to charge him with treating an agent no differently from a balance: just as the balance cannot move without a greater weight on one side, and must move downward on the side with the greater weight, so the agent cannot choose without some motive to choose, and must choose in accordance with the strongest motive. But, Clarke argues, this is to deny the agent any power to act in the absence of a motive, and to deny the agent any power to act in opposition to the strongest motive. It is, in Clarke's view, to deny that there are any genuine agents at all. For it is the nature of an agent to have the power to act or not act. A balance has no such power; it is simply acted upon by whatever weights are placed upon it. As Clarke concludes in his fifth and final reply: