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Leibniz is known for his principle of sufficient reason (PSR), the claim that everything has a complete explanation. But what, according to Leibniz, grounds the PSR itself? While it is generally thought that Leibniz grounds the PSR in his logic, I argue that Leibniz grounds the PSR in his theodicy. God creates the best possible world, and a world in which the PSR is true is better than a world in which it is false. I also examine three other alleged grounds of Leibniz’s PSR. These include the nature of necessary and sufficient conditions, the nature of truth, and the world’s harmony. I argue that these alleged grounds, though not without their merits, are ultimately unsatisfactory as grounds of Leibniz’s PSR. I then conclude by suggesting a new way of understanding the relation between the PSR and another one of Leibniz’s principles, namely the principle of the best.

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Leibniz’s principle of sufficient reason (PSR) is the claim that everything has an explanation. But is Leibniz committed to the necessity or to the contingency of his great principle? I argue that Leibniz is committed to its contingency, given that he allows for the absolute possibility of entities that he claims violate the PSR. These are all cases of qualitatively indiscernible entities such as atoms, vacua, and indiscernible bodies. However, Leibniz’s commitment to the contingency of the PSR seems to stand in tension with his inference of the PSR from his theory of truth. I argue, however, that this apparent tension can be satisfactorily resolved. When it comes to his modal views on the PSR, Leibniz’s position is entirely consistent.

“Clarke, Leibniz, and du Châtelet on the Existence of a Necessary Being”

A common argument for the existence of a necessary being is this: there must be an explanation for the series of contingent beings, but that explanation cannot appeal to any of the contingent beings themselves, so it must appeal to a necessary being (sometimes identified as God). I examine three early modern versions of this argument as advanced by Clarke, Leibniz, and du Châtelet. I argue that only Leibniz’s version survives a famous objection by Hume, which is that the non-existence of a real whole renders the necessary being without any explanatory function.