 In arguing for (1), Spinoza relies on two implicit and related premises. One is the  principle of sufficient reason (PSR) and the other involves his account of causation. Put roughly, the PSR states that every fact has a reason for obtaining; in slogan form, there are no brute facts. Most relevantly for our purposes, if something existed for no reason at all, the fact that it exists would be inexplicable, a violation for the PSR. And for parallel reasons, if something did not exist and there was no reason for its non-existence, the fact of its non-existence would also be a violation of the PSR. As Spinoza puts it, “For each thing there must be assigned a cause or reason, both for its existence [if it exists] and for its non-existence [if it does not exist]. For example, if a triangle exists, there must be a reason or cause why it exists; but if it does not exist, there must also be a reason or cause which prevents it from existing, or which takes its existence away” (Ip11d). Thus, according to the PSR, there must be reasons why each existing substance exists and also reasons why non-existing substances do not exist.