Chuang Tzu and Hui Tzu were taking a leisurely walk along the dam of the Hao River. Chuang Tzu said, "The white fish are swimming at ease. This is the happiness of the fish." "You are not fish," said Hui Tzu. "How do you know its happiness?" "You are not I," said Chuang Tzu. "How do you know that I do not know the happiness of the fish?" Hui Tzu said, "Of course I do not know, since I am not you. But you are not the fish, and it is perfectly clear that you do not know the happiness of the fish." "Let us get at the bottom of the matter," said Chuang Tzu. "When you asked how I knew the happiness of the fish, you already knew that I knew the happiness of the fish but asked how. I knew it along the river."

(Tchuang Tzu)