Zhuangzi and Huizi were crossing the Hao River by the dam.

Zhuangzi said, “See how free the fishes leap and dart: that is their happiness.” Huizi replied, “Since you are not a fish, how do you know what makes fishes happy?” Zhuangzi said, “Since you are not I, how can you possibly know that I do not know what makes fishes happy?” Huizi argued, “If I, not being you, cannot know what you know, it follows that you, not being a fish, cannot know what they know. The argument is complete!” Zhuangzi said, “Wait a minute! Let us get back to the original question. What you asked me was ‘How do you know what makes fishes happy?’ From the terms of your question, you evidently know I know what makes fishes happy.

“I know the joy of fishes in the river through my own joy, as I go walking along the same river.”