The wise Zhuangzi and the clever Huizi were strolling on the bridge over the Hao River.
Zhuangzi said, "Look how the fish are swimming so freely and leisurely in the water. That is the joy of fish!"
Huizi replied, "You are not a fish. How can you know the fish are joyous?"
Zhuangzi said, "You are not me. How can you know that I do not know the fish are joyous?"
Huizi argued, "I am indeed not you, so I do not know what you know. But you are certainly not a fish, so it is impossible for you to know the fish's joy. That is certain."
Zhuangzi concluded, "Let us go back to your original question. You asked me, 'How can you know the fish are joyous?' This question implies you already knew that I knew it when you asked. I know the fish's joy from my vantage point here above the Hao River."