Phaedo

At one point in the dialogue Phaedo [pronounced Fay-doe], Socrates has to meet an objection that Simmias poses to the notion of immortality of the soul.

Simmias is at first reluctant to state his doubts. After all, Socrates will take the hemlock soon, and one does not quarrel with the self-consoling thoughts of a man about to die! But Socrates encourages him, and Simmias says that the preceding discussion has proven the duality of body and soul to his (Simmias') satisfaction. But...here comes a big "but".

"One might also make the same case about harmony and a lyre and its strings, that on the one hand, harmony is something invisible and without a body ... whereas the lyre and its strings are physical and corporeal and composite and earthy and are akin to the mortal."

From this duality is does NOT follow, Simmias points out, that the harmony will survive the death of the lyre. If someone cuts the strings, the music ends.

"If then the soul happens to be a particular harmony, it is clear that, when our body is slackened or stretched without measure by diseases and other evils, the soul ... must in fact immediately be destroyed, even if it be most divine...." [Sounds like John Searle's view of the mind-body problem, BTW.]

How does Socrates respond? It takes some time -- the dialogue moves in zig-zags, not straight lines. When we in time we come back to this issue of the lyre and harmony, Socrates says that some harmonies are more harmonious than others. Harmony, then, is a matter of degree. This is not the case with the possession of a soul. If I understand the point here, Socrates/Plato is arguing that "possession of a soul" is a binary matter. No one person is more ensouled than another.

"All the souls of us living are equally good, if indeed, souls are, by nature, the same as this itself: Soul."

Thus, the analogy fails, and Simmias lays aside his own objection to immortality.

Contemporary philosopher Anderson Brown translates that argument into 21st century lingo, in a lively way.

Brown sees Plato as saying that we don't simply find material things and discover that you can pluck them and get music. We create material things for that purpose. A manufacturer created the lyre, stringing it together just so, in order to allow it to carry a harmony. Thus: harmony precedes the lyre. Harmony inspired the lyre. So the duality of harmony and lyre is one in which the intangible side of the dualism both precedes and survives the tangible side. It supports Socrates' contention, rather than weakening it.

I don't really see in Phaedo what Brown sees, but he seems to have given a lot more thought to it than I have, so I'll take it for granted this is there somewhere.