I examine Spinoza’s use of the term quatenus. It is, I argue, an operator working in the context of a broader logical theory and blocking certain inferences that, according to critics such as Pierre Bayle, lead Spinoza’s metaphysical system into absurdities. I reconstruct this crucial theory from some treatises on logic to which Spinoza had access. I then show how a later logical theory—that of the Port-Royal Logic—does not permit Bayle’s troublesome inferences to be blocked by the use of terms like quatenus. Most likely, Bayle was thinking in terms of the later theory, Spinoza in terms of the earlier.