The dialogue takes place in Socrates' prison cell, before he is to be executed by drinking hemlock. In it, he seeks to prove the immortality of the soul, the existence of the afterlife, and immorality of suicide. This has made the piece influential among Christian scholars, although the beliefs in reincarnation and the transmigration of souls are discussed favorably. A great deal of the dialogue is given to discussion of Plato's well-known "theory of forms."
Compared to other Socratic dialogues of Plato, the Phaedo is written in an unusual form, as the entire dialogue is presented within another dialogue taking place after Socrates' death: that between Phaedo (who was present in the cell) and Ephecrates (who, not having been present in the cell, was eager to hear of Socrates' last thoughts before dying). The main characters engaging in the inner dialogue are Socrates, Cebes, and Simmias.
- "What a queer thing it is, my friends, this sensation which is properly called pleasure! It is remarkable how closely it is connected with its apparent opposite, pain. They will never come to a man both at once, but if you pursue one of them and catch it, you are virtually compelled always to have the other as well; they are like two bodies attached to the same head." (61b)