Chuang Tzu 2.11

The Penumbra asked the Shadow, saying, "Formerly you were walking on, and now you have stopped; formerly you were sitting, and now you have risen up—how is it that you are so without stability?" 

The Shadow replied, "I wait for the movements of something else to do what I do, and that something else on which I wait waits further on another to do as it does. My waiting—is it for the scales of a snake, or the wings of a cicada? How should I know why I do one thing, or do not do another?" 

"Formerly, I, Kwang Kâu, dreamt that I was a butterfly, a butterfly flying about, feeling that it was enjoying itself. I did not know that it was Kâu. 

"Suddenly I awoke, and was myself again, the veritable Kâu. I did not know whether it had formerly been Kâu dreaming that he was a butterfly, or it was now a butterfly dreaming that it was Kâu. 

"But between Kâu and a butterfly there must be a difference. This is a case of what is called the Transformation of Things."