1. There are two kinds of existences: (a) the visible world that we perceive with our senses, which is human, mortal, composite, unintelligible, and always changing, and (b) the invisible world of Forms that we can access solely with our minds, which is divine, deathless, intelligible, non-composite, and always the same (78c-79a, 80b).

2. The soul is more like world (b), whereas the body is more like world (a) (79b-e).

3. Therefore, supposing it has been freed of bodily influence through philosophical training, the soul is most likely to make its way to world (b) when the body dies (80d-81a). (If, however, the soul is polluted by bodily influence, it likely will stay bound to world (a) upon death (81b-82b).)

iii. The Affinity Argument (78b-84b)

http://www.iep.utm.edu/phaedo/#SSH3biii