*****WARNING*****
I think I'll have to reread tonight's material, having had a quite seriously wrong picture of psychic harmony in mind as I was reading. The translation in the Cooper edition (Grube's) consistently, when Socrates and his interlocutors are thinking through the consequences of the soul's being a harmony, refers to a harmony
of elements. Now, 'element' usually translates
stoikheion, which is often a very specialized, technical term--Aristotle, at
Met. Γ (1014a), lists uses of the term, and it is quite clear that its range is far narrower than simply 'constituent' or 'part.' A central--perhaps, depending who you ask,
the central--use of the term is for the letter of a word; also, it is no accident that Euclid's treatise is the 'ΣΤΟΙΧΕΙΑ', because the term also (it seems) standardly referred to an important basic proof that was used as a component of other, more complex proofs.
The point is that to say that something is composed out of, or arises from relations between and among,
stoikheia is quite different to say that something is a composition or a relation or product of a relation,
simpliciter. Yet I haven't found any place where what Grube renders 'harmony of elements' actually translates the Greek
stoikheion. I haven't checked all the instances--there are plenty!--but what I've seen in the Greek is either
pragma or a pronoun.
There is one particularly interesting and important sentence, at 92b, where the pronoun Grube is translating with 'these elements' in fact seems to refer to 'the εἶδος and σῶμα of a person.' I haven't looked at the sentence carefully enough to be sure of that, but that would be (i) pretty interesting and (ii) not at all in the range of what is usually meant by 'element.'
So, if you haven't done the reading yet, I'd recommend spending a little extra energy trying to remain neutral, when Socrates speaks of harmony, on the questions of (i) what the harmony is a harmony
of and (ii) what kind of composition or relation the harmony
is.
*****END WARNING*****
One other note: when Simmias says at 92a that he would be 'very surprised' if he ever changed his opinion, the verb there is an optative of θαυμάζω, which I think is an important verb in Plato. If I recall correctly, in the Platonic statement that 'philosophy begins in wonder,' the 'wonder' is a form of θαῦμα.
Anyway, in our translation it appears that Simmias would be surprised if he changed his mind about
one thing, but Socrates has just listed a
set of statements. What exactly is Simmias saying he would be surprised about? (The abandonment of the whole view, or of some specific thesis?) Similar questions apply to Cebes.
In short: I'm just not sure what the dialectical function of those comments is.