The Leibnizian Cosmological Argument reasons from the contingency of the universe as a whole to the existence of a necessary being who provides the sufficient reason for why anything exists rather than nothing. Unlike Thomistic versions that focus on causal series, the Leibnizian argument focuses on explanation: the totality of contingent reality cannot be self-explanatory, since each part of it depends on something else, and the whole inherits the contingency of its parts. The sufficient reason must therefore lie outside the contingent order, in a being whose existence is necessary in itself.
Gottfried Wilhelm Leibniz formulated the argument most influentially in On the Ultimate Origination of Things (1697) and in his correspondence with Samuel Clarke. The argument depends on his Principle of Sufficient Reason, which Leibniz took to govern not only logical truths but also contingent matters of fact. The argument was central to debates over the cosmological inference in early modern philosophy and was attacked sharply by Immanuel Kant in the Critique of Pure Reason, who argued that the cosmological argument illegitimately extends categories of empirical understanding beyond their proper domain. In contemporary analytic philosophy, the Leibnizian approach has been refined and defended by Alexander Pruss in The Principle of Sufficient Reason (2006) and by Joshua Rasmussen, who have developed versions designed to evade modern objections while preserving the inferential structure.
Critics have focused on the Principle of Sufficient Reason itself. The classical objection from Hume — that demanding an explanation of the whole, when each part is explained, may be a fallacy of composition — has been refined by Paul Edwards and Graham Oppy. Peter van Inwagen famously argued that strong versions of the PSR generate modal collapse: if every contingent fact must have a necessary explanation, all contingent facts threaten to become necessary. Defenders have responded with weaker, more carefully restricted formulations of the PSR, generating an ongoing debate about how strong a principle is needed to drive the cosmological inference and how strong a principle is independently defensible.
Among other formulations in the cosmological family, the Leibnizian Argument is methodologically closest to the Contingency Argument, sharing modal categories and the appeal to sufficient reason — indeed contemporary contingency arguments are often described as Leibnizian. It differs from the Kalam version in not requiring temporal beginning. It differs from the Thomistic version in its more explicit and freestanding reliance on the Principle of Sufficient Reason rather than on causal series structures. Ibn Sīnā's burhān al-imkān wa-l-wujūb anticipates the Leibnizian approach by several centuries, operating through the modal categories of contingency and necessity rather than through temporal or causal structures.