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The TERM, "PRINCIPLE OF SUFFICIENT REASON" (hereafter, PSR) was coined by Leibniz, and he is often regarded as its paradigmatic proponent. But as Leibniz himself often insisted, he was by no means the first philosopher to appeal to the idea that everything must have a reason.* 1 Histories of the principle attribute versions of it to various ancient authors.2 A few of these studies include, or at least do not exclude, medieval philosophers; one finds the PSR in Abelard, another finds it in Aquinas. '1 And while Leibniz retains pride of place in these histories, Spinoza is sometimes said to precede him "in appreciating the importance of the Principle and placing it at the center of his philosophical system."4 In this paper, I shall argue that the same should be said of the Islamic philosopher Avicenna. Writing six hundred years before his early modem counterparts, Avicenna routinely and consistently appeals to the PSR in generating his metaphysical system. The paper aims first to establish that Avicenna deserves a position of prominence in histories of the PSR (§1), and then to consider how he addresses certain challenges to the PSR, especially the threat posed by necessitarianism (§11).
Some contemporary philosophers argue that the PSR entails necessitarianism and thus conflicts with the intuition that things could have been otherwise.5 That the PSR entails necessitarianism is judged to count against the PSR. To consider Avicenna's response to this threat is important: it not only helps us understand the nature and extent of his commitment to the PSR but also helps us assess the PSR itself. I will argue that Avicenna disputes the veracity of the intuition that things could have been otherwise by showing that it may be rooted in ignorance of the determining causes of some events. I will also argue that Avicenna's modal ontology calls into question the view that the PSR entails necessitarianism.
The paper's initial aim-namely, to establish that Avicenna deserves a position of prominence in histories of the PSR-is important for three reasons. The first of these is historical accuracy. The PSR is sometimes said to be "as old as philosophy."6 7 It has played a supporting role in several major philosophical systems. Its truth, its implications, and its pemiciousness remain a...