Warning: some content may offend, some words have been changed to protect the innocent.

What a naughty boy I am. Back in August, in the second-to-last paragraph of a review of a TV documentary series aimed at adults about dysfunctional British toffs, I did something I almost never do in print: I swore. Writing about the Spencer-Churchill family of Blenheim Palace, Woodstock, Oxfordshire, I said "... when you have family whose present generation is as f***ed up as this, who cares ... ?"

As it turned out a Mr John Parker of this parish did care, but not about how f***ed up the Spencer-Churchill family is. An "author, writer, speaker" from the North Shore, he fired off a thundering email."Mr Dixon uses asterisks for a reason: the word's offensive. So why choose it for a family magazine?," he fulminated. "I can think of three reasons. One, that Mr Dixon wishes to shock. He has failed. Two, he is terminologically challenged. In which case, he could use a thesaurus. Three, that he is a lazy writer. In which case, he could get up earlier - and use a thesaurus. Could you have a quiet word with him, please?"

Oh dear. Putting aside that I am apparently terminologically challenged and - worse - a lazy writer, why did Mr Parker find this word offensive even though he wasn't shocked by it? And how can this particular word continue to be objectionable to him or anyone else given that even if one never utters it, if you don't hear someone saying it on the street on or the TV once a day then you're probably deaf - or dead.

After all there is almost no escaping four-letter words in modern life, at least according to a recent survey done by Online Opinions in Britain. It found that just 5 per cent of Brits got through a day without hearing someone cursing, with over three-quarters of the 1000 people surveyed accepting that swearing was routine in modern society. New Zealand, one suspects, is little different.

Should we be surprised? Of course not. Around 90 per cent of men and 83 per cent of women reportedly swear regularly. And, according to research done by an American cognitive psychologist, Timothy Jay, around 0.7 per cent of the words used by an average person in a day are swear words, rising to as much as 3 per cent in the particularly sweary. Now before you say that isn't much, keep in mind that the number of personal pronouns (for example I, you, he, she, you, they etc) the average person uses in a day is 1 per cent.

We (almost) all swear and we (almost) all swear with lamentable regularity. So even if you didn't read my column back in August like Mr Parker did, then the chances are pretty good that you used or heard the same word without asterisks on that very same Saturday. This would no doubt explain why Mr Parker (or most other people) wasn't shocked. He's heard it all before.

As to his other allegations? Well putting aside what I assume is a facetious suggestion that I'm terminologically challenged, the bigger question is this: is swearing lazy language and therefore a bad thing altogether? This, it turns out, is a questions for the ages.

When in Rome, one might have said something was merda (shit) or called someone a cinaedus (the passive partner in male-male sex). During the Middle Ages, you could truly shock your fellow serfs by shouting "by God's bones!", while a few hundreds years later Queen Elizabeth I appalled her court by peppering her speech with "God's death!".

During Victorian times you could scandalise polite society by using the words "trousers" and "leg" and in the very early 20th century if one used "bloody" one was being bloody offensive.

In New Zealand, according to Victoria University lexicographer Dianne Bardsley, swearing has largely followed British (and Australia) patterns, though occasionally with a Maori twist ("tutae happens", for example, for "shit happens"). In fact there is only one swear word in Bardsley's recently published Book Of New Zealand Words: "buggered", which is used to mean beaten or finished rather than you know what. Our troops in both world wars popularised the word - but not in mixed company obviously. This would be why All Black Peter Jones caused a furore when he described himself, after the team beat South Africa in 1956, as "absolutely buggered" on live radio. As late as the 1970s, then leftwing radical Tim Shadbolt and Aussie feminist Germaine Greer managed to get themselves arrested here for using the really rather mild "bullshit" in a public place.

Swearing (and the offence it can cause) is one of the constants of language, then. This, writes American academic Melissa Mohr in Holy Sh*t, a recently published and highly entertaining history of profanity, is because swearing performs a crucial role.

"It would be disingenuous to deny that swearing is in some way 'bad language'," Mohr writes. "Swear words are offensive, they are vulgar, and they can certainly be overused.

But ... they are the most powerful words we have with which to express extreme emotion, whether negative or positive. They insult and offend others; they offer catharsis as a response to pain or to powerful feelings; they cement ties among members of groups in ways that other words can't.

"To put it another way, language is a tool box and swearing is a hammer. You can try to pound a nail into a piece of wood with the handle of your screwdriver, with your wrench, or your pliers, but it's only your hammer that's perfectly designed for the job."

Swear words, Mohr says, have a fascination as well as power, which is why a nice mother of two like her (who also happens to an authority on medieval and renaissance literature) decided to write a book about them which the prestigious Oxford University Press has chosen to publish it.

"I got very interested in how these words affect people," she says by phone from her home in Somerville, Massachusetts. "Language can do lots of things ... but swearing has this immediate emotional and physiological effect on people. As a nice, inoffensive woman, people rarely swear at me. But when they do it's kind of amazing, it's like 'wow!"' She laughs. "I guess I was interested in how those words got their power."

The power comes from taboo, which makes a history of swearing a history of what mattered to us. "People swear about what they care about, and did in the past as well," Mohr says. "Swearing offers a map of some of the most central topics in people's emotional lives over the centuries."

Her book isn't called Holy Sh*t for a laugh or to boost sales. It's has the title because these two things - the holy and the bodily - have for the most part been what people have found taboo over the last 2000 years. Sometimes, like during the Middle Ages for example, it has been oaths related to the holy which were the most taboo ("by God's bones!"), at other times, in the 20th century for example, it was words related to bodily functions and sex.

"Over the centuries these two spheres of the unsayable - the religious and the sexual/excremental, the holy and the shit, if you will - have given rise to all the other 'four-letter words' with which we swear," Mohr writes. "A history of swearing is a history of their interaction and interplay. Sometimes the holy is the main source of swear words, sometimes the shit, and sometimes the two fields have joined in what we would consider unusual combinations ... as demonstrated by one precocious four-year-old at my son's nursery school, who responded to something his mother said with 'Well, f**k me, Jesus!"'

Swear words, scientists have discovered, aren't, like the rest of language, products of higher brain function, but instead are stored in the limbric system, the "old" part of the brain responsible for emotion, fight-or-flight reactions and the autonomic nervous system, which regulates your heart rate and blood pressure. This is why the most reliable measure of what defines swearing, Mohr tells me, is the physical reaction it causes.

"I would define swearing more narrowly than some people. I would say that a swear word is word that has very strong physiological affects like making your heart race ..."

Or even a word that assists dealing with pain. Researchers at Keele University in Britain revealed a couple of years ago that swearing your head off when you stub your toe or bang your head helps wonderfully. They proved this by measuring the number of seconds subjects could keep their hand in a bucket of icy water when using swear words or neutral words. Naturally swearing helped more than saying something like "fudge".

People who did not swear regularly in their daily lives lasted 140 seconds - twice as long as when they used a neutral word. Conversely those who swore up to 60 times a day could only last 120 seconds when using both swearing and a neutral word.

From which you might conclude this: the higher the long-term use, the higher your tolerance to, if not pain, then the rude words themselves. Though not always ...

I can still remember the shock. The first episode of HBO's terrific Western series Deadwood was the first time I'd heard the c-word used on television. And not just the c-word. I have no problem with profanity but the show's first 55-minute episode was like some sort of world record attempt with three uses of the c-word, 49 uses of the f-word, eight of motherf*****, seven of shit, two of pissing and one each of son of a bitch, bastard and sweet-assed. That's 1.3 curses a minute! Deadwood creator David Milch's defence was simple: context. He told the Guardian that bad language is a form of armour, a way to assert strength and masculinity. "Any society that is poor or lawless or violent uses profanity as a way of protection. Go to any inner-city ghetto from Los Angeles to Glasgow and you will find an excess of foul-mouthed men."

The fictional 1870s hamlet of Deadwood was just that kind of town.

Deadwood wasn't actually the first time the c-word had been used on American television. In what was viewed as some sort of culture landmark, (or lowpoint depending on your view), an episode of HBO's Sex and the City used the word in 1998.

As appalling as the c-word is to many people, it's offensive to fewer people than it used to be. We know this because the Broadcasting Standards Authority (BSA) has been asking people what words they find unacceptable on television and radio since the year that that Sex and the City episode screened in New Zealand, 1999.

Since then, the survey has been carried out three times - mostly recently in March - and while the order of the 31 words on BSA's list has changed little since 1999 almost every word has a significantly lower level of unacceptability now than it did back then. The c-word, still by-far-and-away the most unacceptable word, has dropped from 79 per cent (of people finding it unacceptable) in 1999 to 70 per cent in 2013.

Another common swear word, f***, which is number seven on this list, is unacceptable to just half of people now, but was unacceptable to 70 per cent of people in 1999.

Compared to the last BSA survey, done in 2009, the 31 words and phrases have become more acceptable when used in comedies, drama, reality TV and after 8.30pm.

(Unsurprisingly men and the young are more accepting of strong language as well as those - this may surprise- with high household incomes).

The big question is why we're getting more tolerant. The 2013 BSA report, prepared by the Nielsen market research company, said its survey does not identify the contributors to "this softening in attitude", but "it's possible", it concludes, that "desensitisation is occurring through greater exposure". Well, no shit kidding! The television we watch today - particularly after 8.30pm - is nothing like the television we were watching 20 years ago. There is more sex, more violence, more swearing - more everything.

And of course we all swear more too. Bardsley says our culture's general evolution toward "informality" is mainly responsible for that. "We can now say what we like. I wouldn't say [we swear more because of] declining standards, because I find that a very subjective and even a quite judgmental term. It is simply increasing informality.

"I also think with the frequency of useage, the more we are exposed to something, the more acceptable and so-called normal it becomes."

But here's the paradox: while the new normal means that those naughty four-letter words are becoming less offensive to more people, there are other kinds of words - or phrases or ideas - that have rushed to fill the space.

Racial epithets, while they have always been offensive, have grown in power to outrage.

The n-word, for example, is second on the BSA's list and using it, and words like it, can be illegal. The Human Rights Act 1993 limits freedom of expression about race, with section 61 prohibiting "expression that is threatening, abusive, or insulting, and considered likely to excite hostility against or bring into contempt a person or group of persons on the ground of their colour, race or ethnic or national origins."

One of the frontlines for what is offensive is stand-up comedy. The owner of Auckland's Classic comedy club and long-time comedy guru Scott Blanks says what is offensive in comedy has definitely changed in the last decade.

"Now days in comedy there are words like n***** and Muslim and Holocaust. They are what I call trigger words. Rape is one of the big four-letter words in comedy at the moment," Blanks says. "I don't think swearing has the impact on an audience these days as much as certain topics. Probably the things that rile an audience the most are topics like rape and paedophilia."

Or as, comedian Benjamin Crellin found, highlighting hypocrisy. Crellin, who spent the last eight years working in London, was headlining a new material night at well-known comedy club Leicester Square Theatre a couple of months ago when an audience member, after standing up and loudly objecting to the content of one of Crellin's jokes, threatened him physically before leaving the club. The punter then - can you believe it? - called the police to complain about the joke.

"I went into the joke - ironically it's actually an award-winning joke from 2009; it won me most offensive/progressive gag at the New Zealand Comedy Guild awards- anyway I was halfway through that joke, I didn't quite get to the punchline. It's a joke that compares landmine victims to the victims of paedophile and which one is worse. It's very funny, I'm very proud of it. Anyway I didn't get to the punchline ... this guy just flipped out."

Police spoke to theatre staff soon after. There were, however, no ramifications for Crellin - though he does still sound mystified by the experience.

Another local comedian James Elliott, who also happens to be a lawyer, says there's been an increased tolerance for swearing at the same time as there's been a raise in political correctness around what people will take offence at. "I just read a book by an Australian about the culture of taking offence. You just never know quite where people are going to be on that. So you've got a sort of thinning skin in areas where people will take offence and then a thickening about actual language. It's a slightly inverse relationship."

In the 21st century, he reckons, you've got to be more careful about actual subject matter, about content, than you do necessarily about swear words.

Imagine a world without swearing? Well in 1973 a Yugoslav philologist called Olga Penavin did exactly that, predicting that the positive power of socialism would render swearing extinct. Penavin's reasoning went like this: socialism would lead to utopia, in a utopia there would be no conflict and if there was no conflict there would no need for swear words ... I suppose we can call that another massive fail for socialism, then.

And it is probably just as well too. Although my correspondent John Park and, to a certain extent lexicographer Dianne Bardsley, are of the view that swearing is lazy language, Mohr completely disagrees. Swearing is important to us because it's a safety valve, allowing people to express negative emotions without resorting to physical violence.

"They are cathartic, relieving pent-up emotions in ways other words cannot. Take away swear words, and we are left with fist and guns."

American cognitive psychologist Timothy Jay, in a 2009 paper on swearing, says that from an evolutionary standpoint swearing is an unique human behaviour - and one that developed for a purpose.

"Taboo words persist because they can intensify emotional communication to a degree non-taboo words cannot," Jay writes. "'F**k you!' immediately conveys a level of contempt unparalleled by non-taboo words; there is no way to convey 'F**k you!' with polite speech."

Quite right too. So next time you swear, do so in full and proud knowledge you have history, evolution and simple practicality on your side.

Holy Sh*t by Melissa Mohr ($40 Oxford University Press). The Broadcasting Standards Authority "What Not Swear" is at bsa.govt.nz