At TED, Richard Dawkins told a marvelous story I’ve never heard before.

We’re now so used to the idea that the Earth spins, rather than that the Sun moves across the sky, it’s hard for us to realize what a shattering mental revolution that must have been. After all, it seems obvious that the Earth is large and motionless; the Sun, small and mobile.

But it’s worth recalling Wittgenstein’s remark on the subject. “Tell me,” he asked a friend, “why do people always say it was natural for man to assume that the Sun went round the Earth, rather than that the Earth was rotating?”

His friend replied, “Well, obviously because it just looks as though the Sun is going round the Earth.”

And Wittgenstein replied, “Well, what would it have looked like, if it had looked as though the Earth was rotating?”