volume 10, no. 7 july 2010 PSR Michael Della Rocca Yale University © 2010 Michael Della Rocca <www. philosophersimprint. org/ 010007/> “Has not everybody made use of this principle upon a thousand occasions?” —Leibniz to Clarke 1 P lease don’t let me start. The beginning is so seductive that once I get going, it’s hard for me to stop. And even when I am relentlessly pursuing this line of thought, as I am wont to do, a part of me really wants to stop because I know that this pursuit can win me few friends and allies. And where does this line of thought lead? Straight to the Principle of Suicient Reason, the PSR, that for- lorn principle according to which, for each thing (object, state of af- fairs, or whatever) that exists or obtains, there is an explanation of its existence, there is a reason that it exists. 2 I can see now how it will go because I have rehearsed it all be- fore. I begin with certain extremely natural and well-nigh undeniable claims concerning explicability, concerning whether certain things can be allowed to be inexplicable. Then, on this uncontroversial basis, I seek gradually to ratchet up the pressure on you to accept the PSR, to embrace the view that no fact is inexplicable — or so the oft-rehearsed progression goes. I then build on these moves to mount a more direct argument for the PSR that, perhaps, makes the pressure to accept the PSR extremely diicult to resist. But I know in advance how quixotic my attempt will be, for it is quite an understatement to say that the PSR has fallen on hard times and that pleas on its behalf now almost universally fall on deaf ears. This is so for many reasons. First of all, previous attempts to argue for the PSR have been remarkably inefectual. 3 Second, there have been 1. In Leibniz, Philosophical Essays, translated by Roger Ariew and Daniel Garber (Indianapolis: Hackett, 1989), p. 346. Versions of several paragraphs in the irst half of this paper appear also in Della Rocca, Spinoza (New York: Rout- ledge, 2008), chapter 8. 2. Alternatively, if we focus on truths instead of things or states of afairs, we might say that, for each truth, there is an explanation of its truth. 3. See, e. g., Leibniz, Confessio Philosophi, in Leibniz, Confessio Philosophi: Papers Concerning the Problem of Evil, 1671–1678, translated by Robert C. Sleigh, Jr. (New Haven: Yale University Press, 2005), p. 33. See also the discussion in Robert Adams, Leibniz: Determinist, Theist, Idealist (New York: Oxford Univer- sity Press, 1993), p. 68. Imprint Philosophers’