The philosophical discussion begins as Socrates remarks that a true philosopher ought to welcome death, though suicide is not legitimate. Cebes is puzzled by what seems to be a contradiction-- that those for whom death would be a blessing cannot take their own lives, but must wait for their lives to be taken from them--and asks Socrates to articulate this view. Socrates explains that we are the possessions of the gods, and so have no right to harm ourselves. Cebes replies that this is a satisfactory answer as to why we should not commit suicide, but he is still unclear as to why a philosopher should welcome death. Cebes reasons that if our lives should be devoted to the service of the gods, the most perfect of masters, we should also be grateful for this service and saddened by the prospect of being released.
Socrates answers that his light-heartedness in the face of death comes from the certainty that he will find even better gods and friends in the afterlife. He accompanies this remark with the conviction that there is an afterlife which is good for those who have been good in this life, and bad for those who have been wicked. According to Socrates, true philosophers spend their entire lives preparing for death and dying, so it would be uniquely odd if they were to be sad when the moment of death finally arrived.
Death, Socrates explains, is the separation of the soul from the body. Socrates also has Simmias' agreement that philosophers distance themselves as much as possible from bodily pleasures--food, drink, sex, fancy clothes, etc. Rather, philosophers are only concerned with the well-being of their souls, and want to free the soul as much as possible from associations with the body. Our senses are imprecise and may deceive us, Socrates asserts, so the best kind of wisdom comes from reason alone, when distanced as far as possible from the distractions of the body.
Socrates, with Simmias agreeing, asserts that there exist such things as justice itself, goodness itself, beauty itself, and so on. These things cannot be detected by the senses, but only through the efforts of the unaided intellect. Any inquiry into justice, goodness, or whatever else will only be productive if we have a clear idea of what these things are in and of themselves. Our quest for the truth will be much aided by death if at that point our soul is completely separated from the contamination of the body. Throughout their lives, philosophers, in their search for truth, have attained a state as close to death as possible, trying to distance the soul as much as they can from the needs of the body. Therefore, death should only be seen as a help to philosophers, giving them even greater separation between soul and body.
Socrates also points out that only a philosopher who does not fear death can truly be said to possess courage and self-control. If everyone but philosophers fear death, the only reason a "brave" non-philosopher would face death would be through a fear of something worse than death. Similarly, a non-philosopher practicing self-control would only be doing so in order to indulge a greater pleasure that follows from the act of self-control. These people would be exchanging pleasures for pleasures, pains for pains, fears for fears. The philosopher exchanges all these things for wisdom, the only thing of true value. This pursuit of wisdom will cleanse the philosopher of all the impurities of bodily life and its passions, preparing him for an exalted afterlife among the gods.
In this one section of text we are introduced to a number of ideas that have served as the foundation for much philosophical thinking and debate for the past 2400 years. Foremost among these ideas is Plato's introduction of the Theory of Forms, sometimes translated as the Theory of Ideas. The theory proposes that abstract concepts, such as courage or justice or beauty or goodness, exist as immaterial and unchanging ideas. For example, instances of beauty in the world are only imperfect reflections of the Form of Beauty, and are beautiful only insofar as they participate in this Form. The Form of Beauty itself, on the other hand is perfectly and unalterably beautiful. We know the Form of Beauty through reason alone, and any discussion of beautiful objects without an understanding of this Form is doomed to failure.