In order to address more carefully the question of whether or not the soul coheres as one unit after death, Socrates suggests that his interlocutors ask what sorts of things dissipate and what sorts of things hold together, and then ask of which sort the soul is a member. His answer to the first question is that composite things, made up of many different parts, are liable to break up, whereas incomposite things can suffer no such fate. Thus, he suggests, things that are constant and invariable are incomposite, since they cannot be changed or broken apart.
Socrates goes on to point out that the Forms must be incomposite, since they are constant and invariable, never admitting any kind of alteration. Particular objects in the world, on the other hand, can be said to be composite, as they are in constant variation. Further, Socrates points out, the Forms are invisible, and can only be apprehended by the mind, whereas material things can be sensed by the body. Socrates concludes from this reasoning that there are two classes of things: those that are invisible, invariable, and incomposite, and those that are visible, variable, and composite.
Next, Socrates points out that we are part body, part soul, and makes Cebes concede that the body is classed among the visible, variable, and composite, whereas the soul must be invisible, invariable, and incomposite. Thus, when the soul uses the body as a means to knowledge, it gets access only to the inconstant and variable, and becomes confused. Only when it investigates by itself does it come into contact with those things that are constant, and thus acquires wisdom.
Cebes is then invited to compare these dualities with that of serving versus governing. He is led to agree with Socrates that the soul and the divine are alike in that they govern, whereas the body and that which is mortal are in a subservient position. From this, and the preceding dualities, Socrates concludes that while his body will decay and deteriorate, like all variant things, his soul will live on, like the invariable, incomposite things which it resembles.
Different souls, however, experience different fates after death. Socrates suggests that the soul that has detached itself from earthly cares and has dedicated itself wholly to the life of the mind as found in philosophy will be able to leave this world of inconstancy and decay behind. It will find itself instead among other divine beings, in a heavenly realm of immaterial, invisible, wise souls.
Those whose souls remain attached to earthly cares, on the other hand, will be bogged down by the material objects and desires that contaminate their souls, and will remain on this earth as ghosts until their souls inhabit another body. Each one will be reincarnated as befits the way they have behaved in this life; for instance, a villain might become a wolf, whereas a good citizen who never learned philosophy might become a disciplined animal like a bee or an ant, or even be given another human body to inhabit.