Full context:   Drawing on the words of his teacher Socrates, Plato considered the psyche to be the essence of a person, being that which decides how humans behave. He considered this essence to be an incorporeal, eternal occupant of our being. Plato said that even after death, the soul exists and is able to think. He believed that as bodies die, the soul is continually reborn (metempsychosis) in subsequent bodies; however, Aristotle believed that only one part of the soul was immortal, namely the intellect (logos). The Platonic soul consists of three parts, which are located in different regions of the body: Plato compares the three parts of the soul or psyche to a societal caste system. According to Plato's theory, the three-part soul is essentially the same thing as a state's class system because, to function well, each part must contribute so that the whole functions well. Logos keeps the other functions of the soul regulated.