Full Idea
In the thinking soul, images play the part of percepts, and the assertion or negation of good or bad is invariably accompanied by avoidance or pursuit, which is the reason for the soul's never thinking without an image.
Gist of Idea
In moral thought images are essential, to be pursued or avoided
Source
Aristotle (De Anima [c.329 BCE], 431a15)
Book Reference
Aristotle: 'De Anima (On the Soul)', ed/tr. Lawson-Tancred,H.C. [Penguin 1986], p.208