Are rainbows real? That is, do they exist unperceived?

The Guinness Book of Records says (or at any rate, used to say) that the world’s longest lasting rainbow was continuously visible over Sheffield for some six hours on 14 March 1994. Here's a picture (I had an office in the Arts Tower at the time which is why I know about it!)

Now, did the Book of Records do some research to check that at every single second from 9am to 3pm, someone or other was perceiving the rainbow? I very much doubt it! I guess that the Book of Records supposed that, to establish the record, it was enough to have grounds for thinking that,at any moment in those six hours, someone suitably placed and lookingin the right direction would have seen the rainbow (it was continuously perceivable, though not necessarily continuously perceived).

And the Book of Records is speaking here entirely in accordance with our ordinary ways of talking about rainbows as continuing to exist unperceived. I see a dramatic double rainbow, go to fetch someone to see it, and when we get back to the window say "oh good, it is still there". And what makes it the same rainbow that is still there at those two different times? Indeed, what makes it the same rainbow that is visible at a given time by differently located people, given that it would look to be in a very slightly different location to them? Nice questions! Presumbably the answers will appeal to something to do with the continuity of what would have been seen over time had we been looking, or the continuity of what would be seen if we moved from one viewing position to another.

Anyway, we certainly do talk of seeing the same rainbow again after a temporal gap, when perhaps no one happens to be looking. We do talk as if rainbows can continue to exist unperceived.

But ok, should we talk that way? Given what we know about the mechanisms by which we come to see rainbows as we do, should we really talk about them sometimes as if they are real persisting things than can exist unperceived?

Well, why not? I'm inclined to be pretty relaxed about this. Talk as you like -- so long as you are not misled!

Rainbows are variously like rabbits, rivers, ripples, holograms, and mirror images, in each case in some ways and not in other ways. In different contexts, we might want to stress different similarities or dissimilarities among such things. Perhaps a small child will be helped a bit to understand what is going on if you say "Rainbows aren't really there you know, there isn't a real coloured arch in the sky". But equally, if the same small child starts to think of rainbows as a kind of waking dream or a private illusion, then we might say "Oh it is really there, I can see it too!".

Which suggests that here (as elsewhere) the dichotomy "real"/"not real" is a crude tool -- and what we (seem to) talk about doesn't in fact sharply divide into two neat categories.

But still, the similarities between rainbows and central cases of "real" things are probably enough to give point to those everyday, Book of Records, ways of treating rainbows as real things that can exist unperceived. So we might as well, to that extent, continue to fall in with our ordinary language practice here.

So long as we do not mislead ourselves ...

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