Having completed his Argument from Affinity, Socrates is silent, and a hush falls over the room. Only Simmias and Cebes continue speaking together in low voices. When Socrates prompts them to speak up, Simmias tells Socrates that both he and Cebes have some difficulties with Socrates' argument, but they do not wish to disturb him in his present misfortune. Socrates finds Simmias' reservations amusing, remarking that Simmias must think Socrates has less insight into the future than a swan. When they are about to die, swans sing loudly and sweetly, knowing full well the good fortune that awaits them after death. Socrates too is confident that he will fare well in the afterlife, so he does not consider his present condition to be a misfortune at all. He urges Simmias and Cebes to voice their objections.
Simmias suggests an analogy between the relationship between the soul and the body on the one hand, and the relationship between the attunement of the strings of a musical instrument and the instrument itself on the other hand. Like the soul, the attunement of a musical instrument is invisible, incorporeal and divine, and like the body, the instrument itself is corporeal, composite, and earthly. Just as the attunement of an instrument exists as a result of the instrument itself being held together at the right tension and in the right way, the soul exists in the body through the body's being properly assembled. And if destroying a musical instrument can destroy the attunement of the instrument, why can we not say that destroying a body can destroy the soul that is in it?
Socrates admits he is very impressed with Simmias' argument. Before answering him, though, he asks Cebes to put forth his argument. Cebes says that though he follows the argument that the soul existed before birth, he is still not convinced that it is immortal. Unlike Simmias, he can believe that the soul survives the death of the body, but he does not take this in itself as evidence that it is eternal. He draws an analogy to a tailor and his cloak. A cloak is far more frail and short-lived than a man, and so a tailor will make and wear out many cloaks over the course of his lifetime. But the tailor will eventually die, and his last cloak will outlive him. The same thing, Cebes suggests, could be said about the soul and the body. The body is constantly changing, and, we could say, it is constantly being remade by the soul. But when the soul dies, the body can no longer be remade, and quickly deteriorates and rots. Even though the soul may outlive several bodies, we could still not maintain that it is immortal unless we could somehow show that it suffers no ill effects or deterioration at each death and rebirth.
Both Simmias' and Cebes' objections are taken very seriously by Socrates, and answering them occupies much of the rest of the dialogue. Socrates is also very welcoming and encouraging of objections. He sees them as further fuel for an interesting debate. Here especially, we come to appreciate the literary force of the dialogue form in Plato's writing. Plato does not simply wish to impose his opinions upon us, but rather wants us to think them through and sort them out for ourselves. If we recall the Theory of Recollection, there is a distinction made between our sub-conscious knowledge of Forms that is forgotten at birth, and the re-awakened knowledge of Forms that allows us to give a proper explanation or account of our knowledge. In the Meno in particular, Plato wants to show that it is only through a proper dialectic of questioning that this true knowledge can be brought out. If Plato were to simply explain his theories, then he would not teach us anything. Only through a dialectic method, complete with counter-arguments and objections, can we be brought to consider the matter for ourselves and gain true knowledge of it.
Simmias' objection comparing the soul to the attunement of a musical instrument is closely linked to Pythagorean thought. The Pythagoreans believed in the divinity of music, and in the notion that the motion of the celestial spheres is dictated by perfect harmonies. It is natural, then, for a Pythagorean like Simmias to think of the soul as a harmony. This idea brings in a different view of the soul altogether. In Socrates' account, the soul is something distinct from the parts of the human body, something that enters the body and imbues it life, but that can exist independently of it. For Simmias, the soul is not a distinct entity so much as the force by which all the parts of the body are held together and through which all the parts of the body are related. The soul gives the body life, but has no life independent of the body, in this view. Thus, the soul cannot exist without the body.
Cebes' objection borrows more from Heraclitus. The Heraclitean theory that all is in flux suggests that there is no such thing as enduring physical objects. For instance, my body is slightly different from what it was five minutes ago. According to Heraclitus, this means that my body now is a different body from the body I had five minutes ago. Essentially, Heraclitus applies the principle that you can never step in the same river twice to the whole world, suggesting that at every instant the world is destroyed and remade in a slightly different form. According to Cebes' argument, then, the many bodies that a soul may inhabit are not the bodies of different people spread out over centuries, but the many bodies of one person, each one being remade at every instant.
Plato seems to borrow somewhat from Heraclitus as well, asserting the transience and variance of material objects and insisting that only the invisible and incorporeal Forms are resistant to change. Thus, a Heraclitean argument from Cebes carries a great deal of force. Cebes' interpretation of the relationship between soul and body seems to interpret the soul as being the agent that remakes the body at every instant, causing it to undergo change. But like a tailor who is constantly remaking his clothes, the soul also will slowly wear out and die. In a Heraclitean worldview, not even the soul is immune to change.