Now Socrates launches into the first of five arguments for the immortality of soul.  First, consider the relationship between opposites.  When something changes, it progresses from one opposite state to another.  For instance, something becomes larger from having been smaller.  Something becomes stronger from having been weaker, and faster from having been slower. 

            So is there an opposite to living?  Yes, being dead.  What happens to living things?  They die.  And what, by parity of reasoning, happens to dead things?  They must come to life.  

            Socrates adds a further support for this theory.  If everything changed from opposite A to opposite B, but never from B to A, eventually there would be no As left.  For instance, if people who were awake went to sleep but sleepers never woke up, eventually everyone would be asleep, and no one would be awake.  Similarly, if everything died, but nothing came to life, eventually everything would be dead.  But we observe that life goes on.  So changes of opposites must continue in both directions. 

            Cebes accepts the argument, perhaps a bit too easily.  This argument is an argument from analogy, which provides a plausible grounds for the conclusion, but hardly a rigorous demonstration.  There is a sense in which dead bodies produce maggots, which turn into flies, and so on.  (But the maggots, we now know, arise from eggs laid by flies, not from the dead body itself.)  In any case, Plato needs to establish a much stronger case for the continuity of life and the interplay of life and death.  He here begins a series of arguments in a manner that proceeds from the weaker to the stronger.  He is just getting started in his defense of immortality.