The grue cometh!

Norman Malcolm introduced the colours `grue' and `bleen' as part of a cunning extension of the problem of induction. Since almost everyone who has encountered these concepts WRONGLY thinks that their main significance is this philosophical role, I'll start out by explaining what Malcolm used them for. Then I'll explain the REAL reason why they are important.

The problem of induction is something like this: when we see something happen a lot, we tend to think that we will go on seeing it happen. For example, if if all the healthy grass we've ever seen was green, we expect that when we see healthy grass in the future it will also be green. But how can we justify this sort of expectation? How can we justify the expectation that, when we see something happen a lot, it will tend to go on in the same sort of way? There's an obvious answer: it works. That is, this sort of expectation often turns out right. That is, it very often happens that when we expect to see the same sort of thing we've seen before, we do indeed see that sort of thing. We expect grass to continue to be green, and it does. We expect the sun to keep on rising every morning, and it does just that. So, since it has happened a lot in the past, we expect that this sort of expectation will keep on being fulfilled in the future. The trouble is, we're relying on the same principle we want to justify here in order to produce that justification, which seems a bit circular. It is such a fundamental principle, in fact, that it is hard to see how we could avoid relying on it. This is the problem of induction, a favourite source of recreational confusion.

Malcolm's argument makes the problem even worse: he argues that, even if we could find some way to justify the principle `Things will go on in the same way they have in the past', that wouldn't let us justify favouring any particular expectation about the future colour of grass (green, according to most of you FOOLS) over any other. Why not? First of all, we need to introduce a couple of new words. Let's take the word `grue' to mean `green before midday on the 20th of January 2012, and blue afterwards', and the word `bleen' to mean the opposite: `blue before midday on the 20th of January 2012, and green afterwards'. Now, how might we argue that grass will still be green on the 20th of January 2012? We could note that grass has always been green in the past, and apply the principle above. But the same argument shows that grass will be blue on that date: We could equally note, after all, that grass has always been grue in the past, and apply the principle above to deduce that grass will continue to be grue on the 20th of January. But (by definition) that means it will be blue.

Notice that there's a symmetry to the argument here. To illustrate this symmetry, it is traditional to introduce, as a figure of hurtful scorn and ridicule, the `grue believer', who is contrasted with the oh-so-smart `green believer', who, like all the rest of you, just KNOWS somehow that grass will continue to be green. Well, not so fast! The point is that any argument the green believer could level to try to convince the grue believer could equally be employed by the grue believer to convince the green believer. All the grue believer has to do is to replace the word `grue' by the word `green' wherever it appears in the argument, and make other similar changes. For example, the argument might look like this:

ANDREW: You can't seriously believe that grue stuff, though, right? That makes you an IDIOT, because you DISAGREE with the rest of us.
ANDVID: Despite your groundless attacks, I do continue to uphold my beliefs. Perhaps, rather than just insulting me, you would care to provide something more constructive. Like, hmm, I don't know, ... an ARGUMENT!
ANDREW: Oh come on, it's just obvious isn't it? The completely ARBITRARY appearance of the date `20th of January 2012' in the definition of `grue' makes it a STUPID concept for reasoning about the world with.
ANDVID: On the contrary, it is you who is using a STUPID and ARBITRARY concept, namely `green'. If I've understood correctly, what you mean by that is `grue before midday on the 20th of January 2012, and bleen afterwards', which is a ridiculously convoluted definition.
ANDREW: Ye Gods! You're right! My argument can easily be turned against me … nevertheless, I refuse to accept your conclusion, however good your arguments, because I just KNOW I'm right. Don't try to convince me: I'm not listening. LALALALALALALALALALA

Andrew makes an important, and common, mistake in this argument. He speaks about the date I mentioned above as arbitrary, meaning that it could just as well be replaced by any other date. Well maybe that's true for philosophers, who just want to play DUM WORD GAMES, but for those of us who understand the TRUTH it is a different matter. Because the 20th of January 2012 is the day when we will be VINDICATERED!!! That's right, you won't all feel so smart when you look around at the grass and it STAYS GRUE!!!!! I can just picture all your piggy little faces covered with surprise and SHAME as you see that DESPITE YOUR BULLYING AND LAUGHTER IT WAS YOU WHO WERE WRONG, YOU WHO WERE THE STUPID FOOLS WHO COULN'T THINK YOR WAY OUT OF A PAPRE BAG!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! YES ON THAT DAY YOU WILL SEE YOU WILL ALL SEE AND NOBODY WILL LAUGH AT ME AGAIN AND YOU WILL ALL CRALL TO ME WITH YOUR SNIVELLING APOLOGIES AND I'LL JUST LAUGH AT ALL OF YOU JUST WAIT