Truthiness, according to the American comedian Stephen Colbert, who coined the word in a pilot episode of his hit TV show back in 2005, is "the truth that you feel in your gut regardless of what the facts support".
The phenomenon is the subject of a study by Victoria University PhD student Eryn Newman and her colleagues.
They found that people are more likely to believe something is true if a photograph appears alongside the story, suggesting that photos help "conjure up images and ideas about a claim more easily than if the claim appeared by itself"'.
As Newman says, "When it's easy for people to bring information to mind, it 'feels' right".
Indeed, "truthiness" requires a strong sense of one's own rightness. It's what we have when we can't be bothered with evidence or principles. As Colbert quips, "truthiness and empirical evidence don't mix".
Nowhere is "truthiness" more evident than in the welfare debate.
Last week, while Labour leader David Shearer reprised a lame anecdote about a roof-painting sickness beneficiary in an attempt to appeal to middle New Zealand, Social Development Minister Paula Bennett was demonstrating how truthiness can drive public policy as well as public opinion.
Defending a proposal to drug test beneficiaries despite lack of evidence, Bennett told Radio New Zealand: "I just don't feel that we need to trawl through evidence and give that much kind of evidence to something that is just so obvious."
The policy change had been signalled earlier by Bill English, who said employers had complained that young people couldn't be employed because they couldn't pass drug tests.
How big a problem is this? Who knows? When the Council of Trade Unions asked Bennett's ministry for evidence, it found there'd been "no advice, briefings, papers or reports in the last 12 months", nor any sign of "the much vaunted complaints from employers about beneficiaries failing drug tests".
Bennett said she was acting on information from "the visits, from face to face meetings, I don't know, from some of the international research I've seen ..."
It's unfortunate that the merits of the proposed policy change aren't as blindingly obvious to Ministry of Health officials. As Radio New Zealand reported last week, a Health Ministry document indicates the proposal to cut benefits for job seekers who fail drug tests could cost up to $14 million a year, rather than the $6 million the Government claims it will save.
It also warns that the policy may have unintended consequences on people's health and overall welfare, for example, by driving some recreational users on to harder drugs that stay in the body for shorter periods, so as to avoid positive tests.
How might we judge the difference in opinion? Without the kind of hard evidence Bennett thinks is unnecessary, it seems we're expected to trust her gut.
It's not only the Ministry of Health that lacks Bennett's talent for, I don't know, just knowing, but also the Human Rights Commission.
Last week, the director of Human Rights Proceedings, Robert Hesketh, released Bennett's response to the privacy complaint taken by Natasha Fuller, a beneficiary whose personal details she made public three years ago. Fuller had publicly criticised the cutting of access to a training incentive allowance from which Bennett, when a DPB mum, had benefited. Hesketh said the matter had been resolved "to the satisfaction of all parties".
I doubt that, though I'm not surprised that Fuller had had enough after three years.
As Bennett's letter made clear, Hesketh considered she had breached Fuller's privacy. Bennett didn't accept Hesketh's view; it was just "his opinion", she said later.
Nor did she apologise for breaching Fuller's privacy, though her letter recorded her "regret" and "acknowledgment of the personal cost that the resulting public debate" had caused her.
"I was personally shocked and concerned by the unpleasant, hurtful and personal comments some members of the public made about Ms Fuller ..."
But Bennett isn't shocked or concerned enough to rule out any future privacy breaches should she find herself needing to throw another beneficiary under the bus to score a political point.
As others have pointed out, this is in stark contrast to the code of conduct of Work and Income, over which Bennett presides, which states that people have the right to have their information "kept private and confidential".
But here is where we're supposed to let the matter lie. Is there a principle at stake, or does is it all just come down to Bennett's rock-solid belief in her own rightness?
Given Bennett's defiant tone and refusal to acknowledge wrongdoing or responsibility, it was hard not to agree with Speaker Lockwood Smith's description of her in Parliament last week as showing "less discipline than a 3-year-old child".
Bennett may have good political instincts; I don't doubt that she cares about the plight of the vulnerable and disadvantaged. But social welfare deserves a more principled and less "truthy" approach.