 In E1p11d2, Spinoza states explicitly a variant of the PSR: “For each thing there must be assigned a cause, or reason, both for its existence and for its nonexistence”. Similarly, in E1p8s2, Spinoza argues, “if a certain number of individuals exists, there must be a cause why those individuals, and why neither more nor fewer, exist”. Spinoza’s insistence that even the non-existence of things must be explainable is crucial. It allows him, for example, to argue that were God not to exist, his non-existence must be explainable. Since God is a substance, Spinoza argues, his existence or non-existence cannot be caused or explained externally (Spinoza takes substances to be causally independent of each other); hence, were God not to exist, he would have to be the cause of his non-existence, just as a square-circle is the cause of its non-existence. But since God is not a contradictory entity, He cannot internally rule out His own existence, and hence He must exist (E1p11d).