unmoved mover, and if he is not the unmoved mover, then the motion that defines this world has no ultimate explanation. God must be the “sufficient causal reason for all movement.”17 Calling God “pure act” (or pure actuality or pure active potency) may sound weird, über philosophical perhaps. Point taken. But we need not be afraid of such phrases; they are über helpful, as it turns out. Such phrases communicate, says Aquinas, that God “cannot acquire anything new.”18 His perfection does not increase