Long ago, a certain Chuang Tzu dreamt he was a butterfly— a butterfly fluttering here and there on a whim, happy and carefree, knowing nothing of Chuang Tzu. Then all of a sudden he woke to find that he was, beyond all doubt, Chuang Tzu. Who knows if it was Chuang Tzu dreaming a butterfly, or a butterfly dreaming Chuang Tzu?

Clearly there's a difference.