 In this passage, Spinoza follows the late medieval Jewish philosopher Hasdai Crescas in rejecting the Aristotelian ban on actual infinity (see Melamed 2014). For Spinoza (and Crescas) the existence of an infinite regress of causes is perfectly legitimate. Yet, if all the items in this infinite chain are contingent beings (i.e., “things which do not exist necessarily by their own  nature”[7]),  the chain itself remains a contingent being, and there must be a reason which explains its instantiation in reality. The ultimate reason for the instantiation of such an infinite chain of contingent beings must, claims Spinoza, be a being whose existence is not contingent (for otherwise, the chain will remain merely contingent and its instantiation in reality would not be sufficiently explained). Thus, Spinoza allows for an infinite regress of causes (or explanations) as long as the entire infinite chain is grounded in a  being which exists by virtue of its mere essence.