He said:

"Were it not that new states arise within an abiding cause—each state, in uninterrupted succession, becoming the cause of the next—motion could never come to be; for an unchanging cause cannot give rise to a changing effect."

He also said:

"From this you understand that the disembodied intellect is not, by itself, the source of any portion of motion. It needs another faculty in which volition is continually renewed and which shifts particular spatial positions; this faculty is called the soul. Thus, if the abstract intellect is to be a principle of motion, it must do so as a commander, a representer, a desirer, or something similar, but certainly not as the direct mover. Direct causation of motion must belong—through will—to that which is itself liable to change, so that one act of will follows another without interruption. The First Teacher alluded to a principle helpful in this regard when, in his discourse on the soul, he said: ‘To the theoretical intellect belong intellectual judgments, whereas to this other faculty belong particular actions.’"