How can I tell why I do one thing, or why I do not do another?" Once upon a time, I, Chuang Tzŭ, dreamt I was a butterfly, fluttering hither and thither, to all intents and purposes a butterfly. I was conscious only of following my fancies as a butterfly, and was unconscious of my individuality as a man. Suddenly, I awaked, and there I lay, myself again. Now I do not know whether I was then a man dreaming I was a butterfly, or whether I am now a butterfly dreaming I am a man. Between a man and a butterfly there is necessarily a barrier. The transition is called Metempsychosis.

"For I already have been boy and girl, And bush, and bird, and mute fish in the sea,"- Euripides transcribes in Chrysippus: "But nothing dies Of...