Aristotle viewed the human person as a "rational animal" composed of an inseparable body and soul. He defined the soul as the principle of life, with three levels - the vegetative soul responsible for nutrition and growth, the sensitive soul responsible for senses and movement, and the rational soul unique to humans and responsible for reason, intellect, and will. Aristotle's concept of self was that the soul gives form to the matter of the body, and together they make up the human person.