  Aristotle devotes a great deal of attention to perception, discussing both the general faculty and the individual senses. In both cases, his discussions are cast in hylomorphic terms. Perception is the capacity of the soul which distinguishes animals from plants; indeed, having a perceptive faculty is definitive of being an animal (De Sensu 1, 436b10–12); every animal has at least touch, whereas most have the other sensory modalities as well (De Anima ii 2 413b4–7). In broad terms at least, animals must have perception if they are to live. So, Aristotle supposes, there are defensible teleological grounds for treating animals as essentially capable of perceiving (De Anima ii 3, 414b6–9, 434a30–b4; De Sensu 1, 436b16–17). If an animal is to grow to maturity and propagate, it must be able to take in nourishment and to navigate its way through the world. Perception serves these ends.