 Each link in this causal chain is preceded by infinitely many causes and is followed by infinitely many effects. Each link also provides at least part of the explanation for the existence of the following link. Is the existence of such an infinite regress consistent with the PSR? Spinoza has no qualms about answering this question in the positive. We may legitimately ask what is the cause of each link in the chain, and the answer would be: the preceding link. Spinoza also thinks that we may—indeed, should—ask what is the cause, or reason, for the existence of the entire infinite chain? He simply thinks that he can provide a clear answer to the latter question as well: God (or the being which is the ground of its own existence). Consider the following passage from Spinoza’s celebrated “Letter on the Infinite” in which he criticizes proofs of the existence of God which rely on the impossibility of an actual infinity of causes and effects.