What is common sense?

As the driver attempted to manoeuvre a Ukip election bus out of a car park next to Portsmouth railway station, it slammed into the station canopy and juddered to a halt. On the side of the double-decker was painted in large letters: The Common Sense Tour. It was one of the funnier images to emerge from a UK election campaign characterised by vicious attack and counter attack: if "Don't crash a bus" counts as common sense, Ukip had broken one of its pledges to the electorate before voting had even begun.

The party continued to hammer home the idea of common sense throughout the campaign. While a smaller minibus painted with the slogan Here Comes Common Sense zoomed around Britain, Ukip candidates used the phrase to frame arguments on everything from immigration to breastfeeding in public. But opposing voices used it too. Dr Eamonn Butler from the Adam Smith Institute announced, "Ukip's crackdown on unskilled immigrant labour breaks with evidence, common sense and moral decency." Welsh Lib Dem peer Baroness Randerson described her party's policies as "oozing with common sense", while red and blue MPs rushed to congratulate the common sense of the voters who elected them. "It's been an overwhelming victory for common sense," said Labour's Mike Kane, MP for Wythenshawe and Sale East, while Chris Heaton-Harris, Conservative MP for Daventry, told the media: "I've always believed in the common sense of the British people." But 19.3 million people chose to vote for non-Conservative candidates, while 21.3 million voted for parties other than Labour. Were those people equipped with common sense?

"Like all pieces of asinine political rhetoric," says Hopi Sen, former head of campaigns at the parliamentary Labour party, "[the term common sense] can have a particular meaning and also serve as a symbol of your overall message. But it's hard to know in which sense it's being used, so it can be both meaningful (to those you hope to persuade) and meaningless (to everyone else)." Dictionary definitions explain that common sense is a universal, unarguable agreement on matters of knowledge, judgement and taste. But for 400 years, politicians have applied it to issues of great complexity and nuance, simplifying arguments in a way intended to align their views with those of the average voter – and, in the process, neutralise dissenting voices.

Writers of the late Roman Republic were the first to invoke the term 'common sense' in the way we use it today. Sensus communis hominum denoted a shared sensibility, a collection of thoughts and ideas that couldn't possibly be called into question. 400 years earlier, Aristotle had put forward the idea of koinē aisthēsis, a faculty within the brain that enabled us to automatically perceive the nature of objects around us; but in the mid-17th century Descartes rejected that hypothesis and pondered the more Roman idea of le bon sens. "Good sense is the best distributed thing in the world," he wrote in Discours de la Méthode, "for everyone thinks himself to be so well endowed with it… it provides evidence that the power of judging well and of distinguishing the true from the false is naturally equal in all men. I have never presumed that my mind was in any respect more perfect than that of ordinary men."

As British essayists and commentators began to pick up on this idea of common sense in the early 18th century, it edged its way into political debate. The Spectator, a daily publication that appeared between 1711 and 1712, used the term divisively, to proclaim that the Whigs were correct, while the Tories were not. Other parties noted its popular appeal and made hay with it. A Tory-bankrolled weekly entitled Common Sense: or, the Englishman's Journal, first published in 1737, used it to launch stinging and effective criticisms of the First Lord of the Treasury, Robert Walpole. By this time, the phrase had become, according to Sophia Rosenfeld in her book Common Sense, "a pivot around which even violent disagreements can turn."

Critics were quick to point out the inherent emptiness of the phrase. Voltaire condemned le bon sens as "raison grossière" (crude reasoning), while Samuel Johnson railed against the author of Common Sense: or, the Englishman's Journal, for "sheltering himself in perfect security" behind the title of the magazine. As a rhetorical tool, the term seemed – and still seems – somehow unassailable. "You can't argue with it because it's argumentum ad populum, or appealing to popular wisdom," says Sam Leith, an expert on rhetoric and author of the book You Talkin’ to Me? "If one of us is saying, 'It's just common sense, everyone knows X,' by and large the audience will tend to agree with you. If you argue against that, you're not just taking on the person's argument; you're alienating the whole audience by telling them that they're too stupid to realise that your argument is right."

The power contained within the phrase was fully unleashed in 1776, when Thomas Paine published his Common Sense; Addressed to the Inhabitants of America on the Following Interesting Subjects. The pamphlet, outlining in simple, straightforward terms why the 13 American colonies should break away from British rule, was concise, straightforward and had a huge impact. It became the bestselling publication in America, was read widely across Europe and completely changed public opinion in relation to the question of independence. It also propagated two crucial ideas: that political campaigning should be shorn of ambiguity and complexity, and that good government is founded on common sense.

These two ideas have lost none of their potency. The Common Sense Firearms Licensing Act is currently making its way through the Canadian parliament and looks likely to become law this summer. The Conservative bill, aiming to relax gun controls, would appear to be the only piece of legislation ever to feature the words 'common sense' in the title; but it's been heavily criticised, not only by gun control advocates but also by members of the National Firearms Association, who believe it will have the opposite effect of increasing gun control. It's a nuanced and highly charged topic. Attaching the 'common sense' tag to the bill was evidently an attempt to boil down complex arguments into self-evident truths, but while it's been a vote-winner for Canadian Conservatives, is this simplistic use of language appropriate?

"Most ethos appeals – particularly in politics – are along the lines of, 'I'm one of you'," says Leith. "For example, 'I don't know much about X, but I was brought up by my dad to believe Y'; which I think is a disgraceful thing for a politician to say, but it's so powerful. There's another specialist appeal which says, 'I know more than you about this, and that's why you should trust me', which really should be the way it works in a direct democracy. But the idea of a politician trying that seems increasingly absurd."

We in the west do seem to be developing an allergy to any form of expertise, widening the gulf between a know-it-all liberal elite and regular, down-to-earth folk. Politicians wield the term 'common sense' in an attempt to exploit that divide, and we see the same strategy used by the British media; right-wing columnists such as Richard Littlejohn and Jeremy Clarkson will "tell it like it is" or "call it as they see it", and we either cheer or hiss, depending on our political hue. The comedian Al Murray, in his guise as the xenophobic, self-contradicting Pub Landlord, has mined a rich seam of gags by satirising this kind of thinking, recycling phrases such as "it stands to reason", "it's staring you in the face" and "it's common sense" as he makes a case for British superiority, or bemoans the confused thinking behind hummus.

"Possibly, in this irreligious age, it's an appeal to a higher power," he says. "If you haven't got a way of cohering things, you can appeal to common sense instead. The last thing we want is some professor telling us how to sort out the country: no, what we want is some common sense solutions. In a technocratic society with all sorts of weird problems and imbalances, the chances are that common sense solutions won't fix the problem. But everyone is guilty of making these reductive arguments as we become more post-ideological."

A flick through this year's election manifestos reveals that the phrase is used six times by parties of the right, and just once by parties of the left. While the slogan was first used by the Whigs in the 18th century as a liberal rallying cry, today it sounds far more potent in the mouths of right-wing politicians. There are exceptions: the book Common Sense, written in the 90s by the late Labour MP Tony Benn, argues for the abolition of the monarchy and the establishment of a secular state. But in recent weeks we've heard David Cameron speak of 'common sense' in relation to the repeal of the Human Rights Act and its replacement with a British Bill of Rights. It's a proposal that many British citizens would describe as having little self-evident justification, but Conservatives see this as sound rhetorical strategy.

"The left has always had more of a systematic ideology," says Garvan Walshe, a former national and international security policy adviser for the Conservatives and a contributor to the blog Conservative Home. "[It's] always had grand plans and schemes and sets of principles. When the left accuses the right of being evil, the right accuses the left of being stupid. And part of the accusation of stupidity is that [Labour] take ideas too far, they're not restrained by experience, by reality. You know – 'They're full of highfalutin nonsense, but we're here to make sure that people have jobs and consumer goods and holidays.'"

The left, meanwhile, counters that this stance is anti-intellectual, that the right has run out of arguments so is falling back on the idea of common sense in desperation. "A lot of the things I would regard as obnoxious on the right," says Sam Leith, "such as entrenched prejudices, idées fixes and idées reçues about the natural order of things, are associated with common sense: 'God didn't create Adam and Steve', and so on. But in an innately conservative system, you have to make arguments that things need to be different. Let's abolish slavery, let's create a minimum wage or whatever. The argument on the right is: 'Why should we do it like that? We've always done it this way and that's the way we do it!'"

One thing is evident: arguments that appear to lack sophistication certainly don't lack appeal. Drew Westen, professor of psychology and psychiatry at Emory University in Atlanta, noted in 2007 how Democrats' 'wonkish rationales' were failing to appeal to American voters; and he wrote a book, The Political Mind, in which he advocated appealing to 'the gut'. Then, in the run up to the 2008 election, he authored a handbook for left-of-centre campaigners which argued that most voters are not persuaded by appeals to reason. "The evidence is clear," he wrote, "that the language on the left needs an 'extreme makeover' so that we stop recycling the tired, poor, and huddled phrases… that lost their appeal decades ago and have little appeal in the political center."

Lynton Crosby, an Australian political strategist and consultant on the Conservative party's successful general election campaign, has been lauded as a master of the simplified, stripped back political message. Campaign strategist Ed Staite, who worked with him on Boris Johnson's mayoral campaign in 2008, says: "He has a great capacity to take some quite complex politics and knuckle them down to one or two sentences, which are then repeated over and over again. There are great examples of this throughout political history; but [appealing to] common sense is just one way to make people think, 'Oh yeah, well, of course I can see that, I couldn't possibly disagree with it.'

This tactic doesn't always work. William Hague's unsuccessful attempt to unseat Tony Blair in the 2001 general election was backed by a Conservative manifesto that solemnly stated: "I trust the British people. I trust their common sense. It's time for common sense." While flattery doesn't get politicians everywhere, it's possible to secure huge numbers of votes (as Ukip has demonstrated) by telling people what they think they already know. The truth, however, is that we don't know. The world is complex, and common sense is nothing more than a clever linguistic tactic. Human sacrifice once seemed like common sense. So did slavery. In some parts of the world, female genital mutilation is still considered as such. Common sense is not only culturally specific, but specific to every individual; to bestow an electorate with 'common sense' is to make assumptions that are incredibly hard to quantify and largely based on lessons from history. And, as Duncan J Watts points out in his book Everything is Obvious, history is only run once. He says: "Common sense is not so much a worldview as a grab bag of logically inconsistent, often contradictory beliefs, each of which seems right at the time but carries no guarantee of being right at any other time."

True common sense – although some philosophers will argue whether it exists at all – can only consist of facts as supremely dull as the ones compiled by Open Mind Common Sense, a project set up by the Massachusetts Institute of Technology in 1999. Its aim was to assemble a set of self-evident truths in an attempt to equip computers with a bit of nous. "Every person is younger than the person's mother." "If you drop paper into a flame then the paper will burn." "People pay taxi drivers to drive them places." Notably absent from the OMCS database is any reference to public breastfeeding. Or gun control. Or, for that matter, how to avoid crashing a double-decker bus in Portsmouth.