Canonical defenders of the principle of sufficient reason (PSR), such as Leibniz and Spinoza, are metaphysical foundationalists of one stripe or another. This is curious since the PSR—which says that everything has a ground, cause, or explanation—in effect, denies fundamental entities. In this paper, I explore the apparent inconsistency between metaphysical foundationalism and approaches to metaphysical system building that are driven by a commitment to the PSR. I do so by analyzing how Indian Buddhist philosophers arrive at foundationalist and anti-foundationalist (...) positions motivated by implicit commitments to different versions of the PSR. I begin by introducing the Buddhist principle of dependent origination (pratītyasamutpāda) as a proto-PSR that is restricted to causal explanation. Next, I show how Vasubandhu’s Sautrāntika Abhidharma metaphysics is shaped by a qualified commitment to both causal and metaphysical grounding versions of the PSR. I then reveal how Nāgārjuna’s Madhyamaka metaphysics is driven by an unrestricted and exceptionless commitment to causal and metaphysical grounding versions of the PSR. Finally, I consider how Nāgārjuna’s account may put him in a unique position to respond to a common contemporary objection to the PSR from necessitarianism. I conclude by addressing a competing interpretation on which Nāgārjuna is best understood as an anti-rationalist rather than an uber-rationalist, as I characterize him. (shrink)