The Inner Touch presents the archaeology of a single sense: the sense of being sentient. Aristotle was perhaps the first to define this faculty when in his treatise On the Soul he identified a sensory power, irreducible to the five senses, by which animals perceive that they are perceiving: the simple "sense," as he wrote, "that we are seeing and hearing." After him, thinkers returned, time and again, to define and redefine this curious sensation. The classical Greek and Roman philosophers as well as the medieval Arabic, Hebrew, and Latin thinkers who followed them all investigated a power they called "the common sense," which one ancient author likened to "a kind of inner touch, by which we are able to grasp ourselves."