One day Plato came to Socrates asking for a lesson in reasoning. Socrates temporized for a bit and posed him the following question: "Two men slide down a chimney, one coming out clean and the other dirty. Which one takes a shower?" Plato said that of course the dirty one does. At this Socrates shook his head and explained that since the dirty one looked at the clean one and assumed he too was clean, and the clean at the dirty and derove [stet] a similar conclusion, mut. mut., the clean one took the shower. Plato looked confused so Socrates told him, "think about it; come back tomorrow. We'll start again."
Plato returned the following day and said "I'm ready, Socrates.". So Socrates set him the following problem: "Two men slide down a chimney, one coming out clean and the other dirty. Which one takes a shower?" Plato, being no fool, said, "the clean one, Socrates".
Socrates: If the clean one looks at himself, what does he see?
Plato: That he is clean, of course.
S: And if the dirty one looks at himself, what does he see?
P: Soot and the like, I would guess, Socrates.
S: Does a person take a shower if he sees that he is clean?
P: No, Socrates.
S: When does a person take a shower?
P: When he is dirty, or thinks he is.
S: If the dirty person looks at himself, does he think he is dirty?
P: Yes, Socrates.
S: So who takes a shower?
P: The dirty one, Socrates.
Plato professed to be even more confused at this so Socrates repeated his yesterdaily advice that he think the matter over and return the next day. This being done Plato approached Socrates in the agora and asked him for the next problem, saying he had thought thoroughly about the previous day's lesson. So Socrates set him the following problem: "Two men slide down a chimney, one coming out clean and the other dirty. Which one takes a shower?" At this Plato became nearly incensed, saying, "I do not understand, Socrates. Two days you asked me that same question and the answer was the clean man. Yesterday you asked me that question and the answer was the dirty man. If only one of them took a shower, surely there is no third possibility!" Socrates, giving Plato a sympathetic glance, simply asked, "How could two people go down a chimney and one of them be clean and the other dirty?".
At that moment, Plato was enlightened.