For Plato, the soul is a grounded aspect of human nature; it is innate, and based upon an adequate understanding of human actions. Plato, from observing human tendencies, arrives at the conclusion that there must be three separate portions of the soul. This notion is based upon the fact that people are often drawn towards certain actions while they are simultaneously pulled away from them; an alcoholic may desire a drink, but at the same time may want to resist such behavior. This sort of conflict, residing in a single individual, could be interpreted or explained in a number of ways; Plato, however, rests his explanation upon a principle that he believes to be the truth: "It is obvious that the same thing will not be willing to do or undergo opposites in the same part of itself, in relation to the same thing, at the same time. So, if we ever find this happening in the soul, we"ll know that we aren"t dealing with one thing but many." (Plato, BIV, 463d). In other words, Plato believes that a single entity cannot hold two contradictory opinions or aims at the same time. As a result, he divides the soul into rational, irrational, and spirited parts, because a single person often wills things that cannot possibly coincide. .

             One of the many problems that arise from this particular understanding of the soul is that it is not abundantly clear, from the examples Socrates uses, that Plato"s conception of the irrational soul is truly driven by irrational motives. He uses the natural desire to drink as an illustration. Plato contends that when people are driven towards drink through thirst, this thirst is truly an irrational emotion. Socrates states, "Doesn"t that which forbids in such cases come into play-if it comes into play at all-as a result of rational calculation, while what drives and drags them to drink is a result of feelings and diseases?" (Plato BIV, 439c). Glaucon readily consents to this idea; however, it is not quite so obvious that Socrates is correct.