Socrates and Plato discussed the nature of afterlife in the “Phaedo” dialogue. Among four arguments he proposes in the dialogue there is a so-called affinity argument, which later transformed into one of the basic paradigms of western religious philosophy and world-view. The affinity argument concerns immortality of soul.
Socrates speaks of soul as of immortal substance and contrasts it to body, which is mortal. Although after death the body seems to exist in the form of corpse, it can no longer be considered a human. The soul, in contrast, is invisible and intelligible being, which is an essential element for life of the body, and which continues to live when the body does not longer function.
Body is a sensible reality and soul is ideal reality. As soul can not be observed by humans, it is a part of divine reality, which is to guide and to rule a body by virtue of its kinship to Heaven. Another function of soul is ability to observe intelligible world, which can not be perceived by senses like vision or hearing. For this reason soul is a better and supreme part of person while body is rude and weak.
Basic objections against affinity argument have been based exactly on the parallel with Heaven – Iyre. Simmias noticed, that soul bears harmony of Iyre, and in case Iyre is destroyed the soul will perish.
Then Simmias compares body to Iyre and says that body and soul are integral parts of an organism, so it would be logical to assume that death of the body would mean death of soul. To this another Socrates’ student Cebes supports Simmias’s argument by saying that he is ready to admit that soul enters the body upon birth, but he doubts that soul can survive after physical death.
To support his position Cebes used an example of weavers and cloaks. A weaver can make a cloak which will exist after his death, on the other hands, many of cloaks made by a weaver are lost before his death. Soul is paralleled to cloaks and weavers to bodies.
This means that some souls can survive after death of the body, but sooner or later they will be dissolved so he proposes to "...rather not rely on the argument from superior strength to prove the continued existence of the soul after death." (Phaedo, 87a)
Upon careful evaluation Socrates’ argument appears to be prevailing and the argument by Cebes seems to be baseless. They actually have much similar in premises: soul exists, it can be separated from body, most often upon death and soul can exist after the body is dead.
Their only factual difference is that for Socrates the soul is immortal by nature and Cebes ascribes bodily features to soul and thinks that it is same mortal, as body. Cebes’s argument is, however, baseless, for in order for a soul to enter into body it needs to have a source.
In case it was a part of body, it would not exist without body. And as it can, it must have some outside origin. Socrates’ mentions Iyer and explains the contradiction what Cebes fails to do.
Phaedo (1999), edited by David Gallop. Oxford, Oxford Paperbacks, 144 pages