The Raven

(Taken from 101 Philosophy Problems by Martin Cohen)

An imperial Court Philosopher is often asked to prove things, such as a Baron’s wager in an argument to the effect that:

All ravens are black

To do this, he realised he would have to find all the ravens in the world, past, present and, ideally, future, and check that they were black. This, it looked like, would take a long time. Alternatively, he thought of a (cunning way) of finding all the non-black things and checking that there were no ravens among them.

‘Find all the non-ravens and check that they are not black’ instructed the Philosopher to his assistant, speaking loosely (and getting confused), as non-ravens could be black anyway.

The problem still was that even if they did find at the time checking that every raven was indeed black, it was possible that the next raven along might be, say, green.

But the Philosopher decided to try and brazen it out anyway, and returned to the Imperial Court with what he hoped was proof that all ravens were, indeed, black. He announced to the assembled group:

‘My Lords and Ladies, the answer is, simply, we define ravens as being black. In which case even, say, a green raven is not a raven at all, merely a green bird withal the characteristics commonly associated with ravens, except that of its colour. None-the-less, it most certainly cannot (by definition) be a raven! All ravens really are black!’ There was a ripple of applause at this. But then the Keeper of the Imperial Ravens stepped forward holding a ghastly, sick-looking bird.

‘But what,’ the Keeper asked, ‘is a raven with a disease which makes its feathers temporarily go green?’