Perceptual phantasia comes about through perception. This presumably is the ordinary kind of phantasia, which in De Anima 3.3 is said to be a change produced by the actuality of perception (429a 1-2). Rational or deliberative phantasia is a product of the intellect, which represents the course of action that, on the basis of practical thinking, seems best. This, to be sure, is a very special kind of phantasia. There must be exercises of the capacity for this kind of phantasia which involve 206 Conclusion more than just the preservation and re-enactment of sensory impressions. It must, after all, be possible to employ deliberative phantasia creatively and (precisely) imaginatively in envisaging courses of action which very much go beyond one's past experience. However, Aristotle's discussions of animal locomotion strongly suggest that he takes such reason-generated phantasiai to play a crucial role in rational motivation. Desire results in large-scale bodily movement unless it is impeded, but it is arguably only through phantasia that reason can bring about the physiological changes that constitute the material aspect of desire.⁸It is phantasia's role, as Aristotle puts it, to 'prepare desire appropriately' (De Motu Animalium 8, 702a 17-19).
— Hendrik Lorenz
Aristotle's phrase is worth sitting with: phantasia "prepares desire appropriately." Not triggers it, not generates it — prepares it, as one prepares a room. Desire is already there, already a kind of motion in the body; what deliberative imagination does is orient that motion, give it a direction that reason has found worth wanting. The image precedes the wanting, but the wanting was always underway.
This matters because the modern habit is to treat desire as either brute impulse to be managed or as rational preference to be satisfied — two ways of handling it that both skip the intermediate territory Aristotle is mapping. Phantasia is that territory: a faculty that is neither pure sensation nor pure thought, that can reach beyond stored sensory impressions to envisage what has never yet been experienced. The soul, on this account, moves toward things it has first learned to picture. Which means the question is never simply what you want, but what images are doing the preparing — what your imagination has already been staging as worth having, worth becoming, worth surviving toward. Reason does not stand apart from that process and evaluate it from above; reason contributes to it, feeds images into the system, shapes the very physiological changes that will constitute desire as a bodily event.
Hendrik Lorenz·The Brute Within: Appetitive Desire in Plato and Aristotle·2006