The scene is from Plato's dialogue "Phaedo". Phaedo who was present with Socrates on the day of his execution, narrates the events of that day to his friend Echechrates.
Socrates is condemned by the Athenian to be poisoned to death, on the false charges brought by the trio Anytus, Meletus & Lycon. But, Socrates is not at all worried about death, and converses calmly with his friends on various topics. The conversation inevitably moves onto topics like death, life after death, soul, etc.
Seeing that his friends are surprised at his calmness, Socrates says that "...he, who has the spirit of philosophy, will be willing to die; but he will not take his own life." Death is preferable to life because the true state of man is his soul, and his body and the soul's attachment to the body is only a temporary corrupted state. A man is not supposed to take his own life because, his life is not his own property but that of the gods. The philosopher prefers the true knowledge and wisdom of the uncorrupted soul to the illusions and sufferings of the body.
Having given the Soul a higher plane of existence than the Body, Socrates proceeds to clear the confusion of his friend Cebes that the Soul may perish along with the Body, by giving a set of arguments to prove the immortality of the Soul:
i) Cyclical Argument: Like asleep-awake, hot-cold, odd-even, etc. opposites generally have a tendency to follow each other. Death & Life being opposites follow each other. From life to death and death to life runs the cycle.
ii) Recollection Argument: Many times one kind of information or knowledge may indirectly trigger the recollection of other kinds of information or knowledge. Also people tend to have knowledge about topics which they were unaware of before being questioned about (a priori knowledge). This kind of knowledge is nothing more than recollection, which is possible only due the fact that the knowledge was there in the Soul beforehand.The Soul is not a clean slate (Tabula Rasa) at birth, but has knowledge from its previous births, which could be recollected.
iii) Affinity Argument: The soul resembles that which is invisible, immortal and divine, and the body resembles that which is visible, mortal and earthly. The soul is related to the divine whereas the body is related to the corporeal. Hence the soul and its existence is not limited to the body to which it is temporarily attached.
iv) Absolute Form Argument: Every phenomenon on Earth is an corrupted subset of an absolute and perfect form of itself. The beautiful is a limited representation of the divine absolute beauty, worldly knowledge is a limited representation of divine absolute knowledge, etc. Similarly, the physical life of the body is a limited representation of the "Absolute Form of Life" the soul. Hence soul is immortal.
Everyone around are captivated by the logic of these arguments. But two people Simmias and Cebes are doubtful. Their objections are as follows:
Simmias:- The harmony (music) of the lyre perishes before the lyre itself. How can the soul (the harmony) continue to exist when the body(the lyre) is destroyed?
Cebes:- The Soul may not perish with the body, but that doesn't mean its immortal. A weaver may weave many coats and outlive most of them, but the last coat he weaves shortly before his death outlives the weaver. Similarly, the soul may outlive many bodies, but can get gradually worn out and finally its last body will outlive the soul.
The listeners are dumbstruck. Both are powerful objections in front of which the earlier arguments of Socrates looks invalid. However Socrates takes the arguments one by one and defends the immortality of the Soul.
Before going into the details of Socrates' defense of the Soul's immortality, it may be worthwhile to understand the exact nature in which Socrates understood the term "Soul". Socrates had a materialistic view of the Soul. For him and for most people of those times, heaven and supernatural were physical places. The soul was a material entity just like the body, the only difference being that it has a higher plane of existence, is divine, and immortal.
The following were the arguments Socrates brought forth against Simmias:
i) In case of lyre and harmony, the lyre always influences the harmony and its never the other way around, but the soul influences the body through its thought and will. Hence the analogy is not valid. The body follows the soul but the lyre never follows the harmony, hence lyre-harmony is not analogous to body-soul.
ii) There are different degrees of harmony. A harmony can be lesser or greater in degree than others, whereas there is no such distinction for the soul.
iii) Harmony is a compound composed of the sum of its constituent elements. The soul a single entity and is not a compound.
The argument of Simmias has much relevance today. It turns out the empirical evidence and modern Science favors Simmias than Socrates. Benjamin Libet (1916-2007) has shown that conscious volitional acts start with the body and not the mind. The brain activity leading to a thought impulse happens a split second before we actually become aware of it. If so the lyre-harmony analogy of Simmias holds, and Socrates was wrong in saying that the soul leads the body.
Modern science has irrefutably shown the material basis (in the brain) of mental activities like memory, learning, recollection, etc. Hence, most of the faculties of soul that Socrates identified with (like recollecting, correlating, etc.) are dependent on the material brain. Once again it looks like Simmias was right and Socrates was wrong.