The Principle of Sufficient Reason, the Ontological Argument and the Is/Ought Distinction

Kant's attack on metaphysics consists in large part in his attack on a principle that he names the Supreme Principle of Pure Reason. This principle, it is not often noticed, is the Principle of Sufficient Reason [PSR]. In interpreting this principle as such, I argue that Kant's attack on the PSR (and thereby his attack on dogmatic metaphysics as a whole) depends on Kant's claim that existence is not a first‐order predicate. If existence isn't what Kant calls a real predicate, the PSR is false. While this constitutes a powerful Kantian argument against dogmatic rationalism, it also poses a problem for Kant. For, as I argue, if the PSR is true, Kant's argument that existence isn't a first‐order predicate is false. In this sense, Kant's attack on the PSR is begging the question vis‐á‐vis radical metaphysicians (e.g. Spinoza). Concluding the paper I suggest relying on Kant's 'is'/'ought' distinction in avoiding this circularity, thereby reinforcing the Kantian critique.