A decade ago, Stephen Colbert, the American political commentator and satirist who will soon become host of ABC’s Late Night Show, popularised the term truthy.

We are all subject to confirmation bias – a tendency to find, or interpret, facts to support opinions we already hold.  But truthiness takes us further.  A statement is truthy if we know it to be valid independently of any fact.  Truthiness is the knowledge that comes when conviction is prized over information.  And, as Colbert has explained, there is a profound egoism about truthiness.  Truthy statements are valid not because I feel they are true, but because I feel they are true.

The concept of truthiness evolved in the era of George W. Bush.  Even before Colbert, Ron Suskind (New York Times magazine, October 17 2004) reproduced an account (widely attributed to Karl Rove, the president’s strategist) of the distinction between ‘the reality based community’, which believes that ‘solutions emerge from judicious study of discernible reality’, and the new political world Rove sought to create in which ‘when we act, we create our own reality’.

In his fine book Enlightenment 2.0 philosopher Joseph Heath notes an effusion from former (and prospective) presidential candidate Rick Santorum. The Republican hopeful described in some detail how half of all elderly patients in the Netherlands are euthanized and its fearful residents seek medical treatment outside the country.  Heath observes that Santorum ‘seemed not to recognise that the Netherlands was a real place, where people might hear what he said, and hope to set the record straight’.   But without success – a spokesperson explained to a Dutch reporter, without retraction or apology, that the former senator ‘says what’s in his heart’.

But truthiness is not confined to the right of the political spectrum.  A lengthy article in the magazine Rolling Stone provided a graphic description of a horrific gang-rape of ‘Jackie’, a student at the University of Virginia.  Jackie allowed two years to elapse before telling the story to a visiting reporter.  After the account was published, the Washington Post sent its own reporter, who established, as did the police, that few of the ‘facts’  of the incident checked out.  Rolling Stone withdrew the piece, and the dean of Columbia Journalism School undertook an investigation of the journalistic and editorial failings which had allowed the unsubstantiated account to be published.

But for Jessica Valenti, a Guardian columnist,(8 December 2014) ‘it doesn’t matter.  Jackie is now another woman who is not believed’.  She goes on ‘I choose to believe Jackie.  I lose nothing by doing so, even if I’m later proven wrong’.   Ms Valenti does have something to lose, just as former Senator Santorum does:  her credibility. And the respect of those who still think that opinions should be based on facts and that the sincerity of a false belief does not justify unfounded allegations against others.

There was a time in Britain when statements and information provided by government, if not necessarily correct, would normally be the product of honest endeavour to get it right.  When I began research at the Institute for Fiscal Studies, it was hard work to persuade people that our figures were as reliable as official ones:  today they would laugh at the suggestion that government figures might be more credible than those of the IFS.

Another political satirist, P J O’Rourke, recognised the central role of truthiness in a political campaign in a tongue-in-cheek brief written for the Supreme Court.  ‘In modern times, “truthiness” – a truth asserted “from the “gut” or because “it feels right” without regard to evidence or logic – is also a key part of political discourse’.   He went on to say that ‘it is difficult to imagine life without it’.  Sadly, as the current election campaign shows. he is right.