Is everything that can be imagined real?

A couple of days ago, I went to see the Mythic Beasts special exhibition at the Canadian Museum of Civilization. It's a fascinating collection of artifacts and stories from around the world.

Now, I have previously written about beasts like unicorns that (probably) don't exist. What about the unicorn's cousin, Pegasus?

How can we talk about Pegasus? To what does the word 'Pegasus' refer? If our answer is, 'Something,' then we seem to believe in mystical entities; if our answer is, 'nothing', then we seem to talk about nothing and what sense can be made of this? Certainly when we said that Pegasus was a mythological winged horse we make sense, and moreover we speak the truth! If we speak the truth, this must be truth about something. So we cannot be speaking of nothing.

The quote—or perhaps it's a paraphrase—is from the Wikipedia entry for philosopher W.V. Quine. In the philosophy of language, this is known as the problem of empty names, and I stumbled on it yesterday by chance. But it reminded me of a curious quote I'd seen at the entrance to the exhibition: