Book II, chapter 2 of Aristotle’s On the Soul (De Anima), where he is dividing the powers of the “soul” and naming what makes a living thing a living thing. He distinguishes the “nutritive” power from “sensation”, and gives “touch” as the primary form of sense. The treatise was the standard text on the soul for the scholastics. It stands under this term as the place where “animal” is defined by sensation.
Read in contextThis is the originative power the possession of which leads us to speak of things as living at all, but it is the possession of sensation that leads us for the first time to speak of living things as animals; for even those beings which possess no power of local movement but do possess the power of sensation we call animals and not merely living things.
The primary form of sense is touch, which belongs to all animals. just as the power of self-nutrition can be isolated from touch and sensation generally, so touch can be isolated from all other forms of sense. (By the power of self-nutrition we mean that departmental power of the soul which is common to plants and animals: all animals whatsoever are observed to have the sense of touch.) What the explanation of these two facts is, we must discuss later. At present we must confine ourselves to saying that soul is the source of these phenomena and is characterized by them, viz. by the powers of self-nutrition, sensation, thinking, and motivity.