The desiderative power has been established as that which moves animals. The cognition pertaining to progressive animal motion needs further attention since some animals are extremely simple while others are quite complex. Aristotle has just emphasized that there can be no desiderative power without phantasia and referred to calculative and sensitive phantasia (433b28–30). What if there are animals so simple that they completely lack phantasia, as was suggested in iii 3.428a9–11? What would be the implications for desire and animal motion? And what is calculative phantasia? Does the distinction of sensitive and calculative phantasia call into question the way phantasia was defined in iii 3? Aristotle must confirm that calculative phantasia does not interfere with that earlier account. Moreover, he should show that calculative phantasia fits with the view that desiderative power moves the animal: such phantasia is not moving the animal without involvement of desire.

What is it that moves the incomplete animals (τῶν ἀτελῶν), where by “incomplete” is meant lacking the full range of senses (433b31–434a2)? The animals under consideration have merely the contact senses, touch and taste (ἁφή in 434a1 may apply to both), but none of the distance senses that complete the possible sensitive component of animals. Such animals without distance senses, it will be seen in 434b24–27, do not have progressive motion. Might these animals also lack phantasia, and if so can they have appetite?