Taboo language is the type of expression which is generally considered "socially unacceptable" (at least in more formal situations) and which most people use only as expletives when under stress - a use Steven Pinker in The Stuff of Thought refers to as "cathartic" - though some make much more regular use of them - as anyone who has watched Gordon Ramsay's cookery programmes on TV will know.
Also called "swear words" they are usually connected with bodily excretions, sex or religion, and - but come on, you all know the ones I'm talking about (and if you don't, have a look here). All languages seem to have them, but what "counts" as an offensive expression may be very different from language to language or culture to culture - as this article from the BBC points out.
What interests me here is not so much what they are, but whether and when they are deemed acceptable and how they are treated in the media when they are not deemed acceptable.
First of all, they're on a scale. At the "mild" end in contemporary English are words like bloody. No-one would really be shocked these days at hearing something like It's bloody raining - just when I bloody well wanted to go out; Bloody hell! or the ironic Bloody marvellous!
However, it hasn't always been like this. Wikipedia reports : Considered "respectable" until about 1750, it was heavily tabooed during c. 1750–1920, considered equivalent to heavily obscene or profane speech. Public use continued to be seen as controversial until the 1960s, but since the later 20th century, the word has become a comparatively mild expletive or intensifier.
That certainly accords with my memories of the 50s and 60s when it was seen as much more "shocking". True, I was a child at the time and even today children might well be told off for using even the milder type of swear word. They're words often seen as for "adult" use only. However, there's no question that bloody has definitely changed over the last 60 years in its capacity to shock.
That's true too of words slightly further up the scale - those words that most of us don't use "all the time" but may well do under stress. I was alone at home the other day and knocked a hardback book off the shelf (It was the collected poems of Yeats if anyone's interested). It fell, corner first, onto my bare foot, and I let out a cry of Sh**
And look what I've done. Even though I'm writing about these words, I haven't printed it out - just given enough to let you guess the word and then added asterisks. What is acceptable in spoken English when under pressure is still generally avoided in writing.
But how acceptable is it even in spoken English? I was alone - what if I'd been surrounded by other people? Depending on how well I knew them and our relationship I might well have changed the pronunciation - shit becomes shite - or instead said Sugar! drawing out the initial /ʃ/ phoneme so that there was no doubt what I was thinking but then replacing it with another word. According to the Oxford Dictionaries website, this use of sugar dates back to at least 1883. And it's not just English that uses this sort of replacement expression - see the link for examples from a range of European languages. In English the replacement expression has sometimes become an expletive in its own right - who would have guessed that Jiminy Cricket! is actually a replacement for Jesus Christ! And What the Dickens...?! a replacement for What the Devil... Not me, certainly.
Some words, at the far end of the scale are so "unacceptable" that there are even euphemisms to describe them - The F-word and The N-word being the most obvious.
Much more interesting though is what happens in the media. Let's take TV first. Taboo expletives are often used in reality shows - and what happens? They're neatly covered by a bleep. I'm currently watching a show called Alaska : The Last Frontier about families living self-sufficiently in the extreme weather conditions found in Alaska. They wade through snowdrifts, ford icy rivers, find their cattle have been attacked by bears, fight off wolves - well, the occasional bleep is surely to be forgiven. Having a book of poetry fall on your foot is nothing in comparison.
But what about in fiction? Think of any TV crime series, or thriller - whether a film or a novel. All sorts of dreadful things happen to the protagonists - they get shot, beaten up, are involved in car crashes - but does an expletive ever leave their lips? Never. And it's not only the "heroes", the "baddies" don't swear either. There's nary a bleep to be heard. All fictional characters are obviously far more self controlled than the rest of us. Had that ever occurred to you as you watched NCIS or whatever your favourite series is? Probably not. We accept the unreality of the scripted language as easily as we accept the unreality of the plot.
The only exception I can think of to this is Star Trek - the Klingons used some great expletives and insults - but as no-one knew what they meant, there were unlikely to be shocked letters written to the producers. However, QI'vah is apparently one of the strongest, foulest expletives in the Klingon language, so next time you're talking to the school director and can't say what you really want to, try it. Just make sure s/he's not a Trekkie first.