But since we have, in our work on the soul, treated of imagination, and the faculty of imagination is identical with that of sense perception, though the being of a faculty of imagination is different from that of a faculty of sense perception; and since imagination is the movement set up by a sensory faculty when actually discharging its function, while a dream appears to be an image (for which occurs in sleep whether simply or in some particular way is what we call a dream): it manifestly follows that dreaming is an activity of the faculty of sense perception, but belongs to this faculty qua imaginative.