The previous chapter emphasized that mind that is part of the soul must be unmixed and separate to think all things. This, it was argued, is consistent with the possibility of thinking, for both mind and its principal object, where these are theoretical knowledge and its object, share the condition of being unenmattered. Aristotle now clarifies just what it is that acts in mind to originate thinking if human mind is primarily potentiality to think all things. All he has to explain is what enters into occasioning this thinking, not to go into detail about the way it arises or to account for the development of concepts or knowledge. He merely has to follow out the implications of his remarks ending the previous chapter. Since theoretical knowledge is the same as the knowable, whereas the external sensible object acts upon the sense to make it operate, the intelligible object may give rise to thinking by way of the knowledge already within the soul. He needs to show that the mind can get itself thinking without seeming an impossible causa sui or self-mover.

Aristotle had said in 430a5–6 that one might consider why we are not always thinking. Divine beings will ceaselessly be thinking, but this does not seem to apply for humans. The reason must be that mind that belongs to soul, as he has established, is potentiality for thinking, and whatever is a potentiality can be or not be (see Metaphysics 1071b13–14, b19).