 Commentators have tried various strategies for finessing the apparent circularity in the PI's account of the diversity in matter. Klever (1988) urges that the key to understanding Spinoza's concept of matter is to see that physical nature is not to be conceived as an infinite extended expanse that somehow is put into motion, but as, fundamentally, matter-in-motion (“moles in motu”). According to Klever, “movement and rest in extension are examples of immediate production by God, whereas the face of the universe with its infinite variations is an example of the mediate effects, which are a product of movement in its turn.” On this interpretation, Spinoza, rather than seeing motion as a received quality of matter, conceives “matter as consequence of motion” (Klever 1988, p. 171). This reading arguably answers Spinoza's call to explain the variety in matter through an attribute that expresses eternal and infinite essence. If God creates extended matter, and then, in a separate act, sets it in motion, the attribute of Extension would not suffice as an eternal expression of infinite essence, since it requires God's additional action in its expression of power.