DN 23 describes a series of debates between a monk and a prince, with the prince subscribing to something akin to a materialist position. In one of the sutta’s many similes, the prince describes an experiment he claimed to have performed which seemingly disproved the existence of a soul.
“Suppose they were to arrest a bandit, a criminal and present him to me, saying, ‘Sir, this is a bandit, a criminal. Punish him as you will.’ I say to them, ‘Well then, sirs, place this man in a pot while he’s still alive. Close up the mouth, bind it up with damp leather, and seal it with a thick coat of damp clay. Then lift it up on a stove and light the fire.’ They agree, and do what I ask. When we know that that man has passed away, we lift down the pot and break it open, uncover the mouth, and slowly peek inside, thinking, ‘Hopefully we’ll see his soul escaping.’ But we don’t see his soul escaping. This is how I prove that there’s no afterlife.”
What I find interesting here is the monk’s response. Instead of arguing that the prince’s assumption that future lives require the existence of some atta which transmigrates, he seems to accept that there is something that transmigrates and merely refutes that that soul must be something visible to people:
“Well then, chieftain, I’ll ask you about this in return, and you can answer as you like. Do you recall ever having a midday nap and seeing delightful parks, woods, meadows, and lotus ponds in a dream?”
“I do, sir.”
“At that time were you guarded by hunchbacks, dwarves, midgets, and younglings?”
“But did they see your soul entering or leaving?”
“No they did not.”
“So if they couldn’t even see your soul entering or leaving while you were still alive, how could you see the soul of a dead man? By this method, too, it ought to be proven that there is an afterlife, there are beings reborn spontaneously, and there is a fruit or result of good and bad deeds.”
How should we understand this? What is this “soul” that both interlocutors take for granted if there is a life after this one?