Chuang Tzu - Once upon a time, I, Chuang Tzu, dreamt that i...

Once upon a time, I, Chuang Tzu, dreamt that i was a butterfly. Flitting around and enjoying myself. I had no idea I was Chuang Tzu. Then suddenly I woke up and was Chuang Tzu again. But I could not tell, had I been Chuang Tzu dreaming I was a butterfly, or a butterfly dreaming I was now Chuang Tzu? However, there must be some sort of difference between Chuang Tzu and a butterfly!