Phaedo recounts that he and the other spectators in the room became very depressed upon hearing Simmias' and Cebes' objections, feeling that Socrates' theories were now very much in doubt. Echecrates expresses sympathy, explaining that Simmias' theory that the soul is some sort of attunement has always attracted him. Nonetheless, Phaedo explains, Socrates managed to boost his and his companions' morale, urging them to continue the inquiry. Phaedo slips back into the narrative after this brief interlude. Socrates warns his friends not to become "misologic" and begin hating arguments. This might happen if one becomes attached to every argument one hears, only to discover later that it is false. Too many disappointments of this kind can lead to sophistry and a conviction that there is no truth, since no arguments are dependable and stable. But to do this would be to blame the arguments for one's own shortcomings, and one would be liable never to come to know the truth about reality. Thus, Socrates urges further consideration of his and his objectors' arguments.
After reviewing Simmias' and Cebes' arguments, he asks if they reject all his previous arguments or only some of them. The two men agree that they only reject some of them, and, prompted by Socrates' questioning, agree that they both still find the Theory of Recollection supremely convincing. But, Socrates points out, Simmias is contradicting himself if he maintains both that the soul is an attunement and that learning is recollection. The Theory of Recollection shows that the soul must have existed before birth, but the attunement of an instrument cannot possibly exist before the instrument is made. Simmias acknowledges this contradiction, and accordingly withdraws his objection. The argument from attunement was based only on an ungrounded kind of appeal, whereas the Theory of Recollection is based upon the Theory of Forms, which is a strong and credible hypothesis in Simmias' opinion.
Socrates provides three more arguments to show that the soul is different from the attunement of an instrument. First, he points out that an instrument can be more or less well-tuned, and so can have more or less attunement. A soul, on the other hand, cannot be even remotely more or less soul than any other soul, and in this way is unlike attunement.
Second, Socrates points out that some souls are good while others are bad, and makes Simmias agree that a good soul may be seen as analogous to an instrument in tune, and a bad soul as to one out of tune. But since an instrument in tune has more attunement than one out of tune, and since Socrates and Simmias have already agreed that no soul has more soul than any other soul, this analogy does not hold. If every soul is an attunement, no soul is in discord, and every soul is equally good.
Third, Socrates has Simmias agree that the soul governs the body, compelling it to move and to act. Contrary to this, the attunement of an instrument depends wholly on the instrument itself and the manner in which it is made. The body, on the other hand, has no ability to affect the soul, nor does the soul depend upon it.
The brief interlude in which Phaedo and Echecrates remark on the weight of Simmias' and Cebes' objections is one of only two breaks in Phaedo's account. By this stage, the reader might have even forgotten that the dialogue records Phaedo's conversation with Echecrates in distant Phlius. This break in the narrative may do a number of things. It allows us to pause for breath, and to consider Simmias' and Cebes' objections. Plato may be trying to give these objections as much force as possible, and so does not want to have them refuted as soon as they are laid out. Both Phaedo's and Echecrates' remarks, and Socrates' own exhortations to his friends not to lose spirit, serve to make the arguments seem more weighty.
Also, this interlude serves to remind us of the complex framing of the narrative and of the fictitiousness of the whole account. Plato frames the story in this way--even making explicit mention of his own absence at Socrates' death--to make it clear that he is not describing the events as they actually took place. Instead, he is using that setting as a powerful backdrop against which he can present some of his own views. In reminding us of this fictitiousness, Plato is also reminding us that we are not reading a story, with the intent to find out "what happened," but rather are reading philosophy, with the intent to think for ourselves and to tease out the truth. In this sense, the interlude also serves as an appeal to closely consider the objections ourselves instead of blindly trusting the opinions of Plato (as conveyed through Socrates).
Socrates gives us four reasons to think that the soul is different from the attunement of an instrument: (1) the soul can exist before the body is made, (2) there are no degrees of soul like there are degrees of attunement, (3) if the attunement argument were correct, it would imply that no souls were better or worse than any other souls, and (4) the soul is master of the body. We should note that Plato clearly has more faith in the Theory of Recollection than in any of his other theories for the immortality of the soul. Simmias' objection is derived from the Argument from Affinity, but this, it seems, cannot stand up to the Theory of Recollection.
A final point of interest is that Socrates' remark, that a frustration with arguments might lead to the position that there is no truth, is a subtle rebuke of the Heraclitean flux doctrine.