The first point is that even the naughtiest words are controlled by ordinary grammar. For example, you can say "I missed the fucking bus", but not "I missed the fuck bus". But simply letting off steam requires "Fuck!", not "Fucking!" All this makes good grammatical sense if "fuck" is a verb and "fucking" is an adjective.
Naughty adjectives are just like other adjectives: you have to glue them to a noun. They toe the grammatical line and salute when spoken to. In fact, if anything they're more tightly controlled than other adjectives are, because they can't stand after is.
For example, although a big book is a book which is big, a fucking mess isn't a mess which is fucking. The same goes for all the other adjectives - "bloody", "shitty" and so on.
That fact is worth thinking about. Even at the point where we're feeling most controlled by pure emotion and kicking hard against the rules of society, we're actually following the rules of grammar in a very meek and mild way.
Like any well-behaved verb, "fuck" has imperative forms (fuck you, fuck me, fuck this, fuck off), a derived noun (fucker) and two derived adjectives (fucking, fucked). And so on - all very instructive if you're looking for evidence that grammar really matters. Just imagine the social consequences of not knowing the grammar of swearing!
There's even more to the grammar of naughtiness than that. There's one bit of English grammar where the grammar demands something more or less naughty:
* What the hell am I supposed to do about it?
* Where the fuck did I put it?
And so on.
Welcome to interrogative pronouns! Any interrogative pronoun can be spiced up by a dash of emotion - who on earth, why in heaven's name, where the devil, and so on. Some of these are not particularly naughty, but you can always go over the top with "the fuck". (Ok, this isn't a verb; English verbs can turn quietly into nouns - think of "I had a walk".) This corner of English grammar is well-known by all of us, but unexplored.
We're not saying it's appropriate for all classrooms, but it is a reminder that language carries feelings as well as thoughts. And you could always do a censored version using less naughty words.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VISchool, Bury St Edmunds, Suffolk