Chuang Tzu and Huih Tzu were crossing The Hao river by strolling over a dam built across it.

Chuang said
“See how the free the fishes leap and dart,
that is their happiness.”

Hui replied
“Since you are not a fish,
how do you know what makes fishes happy?”

Chuang said
“Since you are not I,
how can you possibly know that I do not know what makes fishes happy?”

Hui argued
” If I, not being you, cannot know what you know,
It follows that you not being a fish cannot know what they know.”

Chuang 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 term of your question you evidently know
that I know what makes fishes happy.”

“I know the joy of fishes in the river
Through my own joy as I walk along the bank.”