This past year, the Oxford Dictionaries chose “post-truth” as its word of the year in a nod to the idea that objective facts “have become less influential in shaping public opinion than appeals to emotion and personal belief.” Indeed, the ideas of truth, fact, “alternative facts,” and “fake news” have become major preoccupations of the political moment. It’s led to a rise in fact-checking as a profession, but not all fact-checks are equal. Just ask Peter Canby, a stalwart of the legendary fact-checking department of The New Yorker since 1978.

In a wide-ranging conversation that took place in a packed classroom of the Columbia Journalism School Monday night, Canby recounted how fact-checking has changed over the years under three different New Yorker editors: William Shawn, Tina Brown, and David Remnick. In that time, the team has doubled, and now at least half of New Yorker fact-checkers speak a second language, including two who speak Russian and another fluent in Arabic. The pace of the work has also increased alongside digital technology. “We couldn’t possibly turn around the pieces that we have on the timeframe we have without the internet,” says Canby.

People who have never been involved in journalism, in fact-checking, think the world is divided into facts and opinions, and the checkers just deal with facts.

In the early days of his tenure, fact-checking was a more restricted and editorially delineated process than it is now. The story that changed the game, Canby says, was a Janet Malcolm piece about the Sigmund Freud Archives that went all the way to the Supreme Court after its subject disputed quotations that were attributed to him. “The Supreme Court opinion, which Justice Kennedy wrote, basically said that the magazines were responsible for quotations in a way they hadn’t previously been seen to be,” says Canby. At that point, fact-checkers became even more important to the editorial process. “We started getting notes, and tapes, and transcripts from our writers, and that enabled us to look at the fabric of the interviews that people do with their subjects.”

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Aside from the bread-and-butter work of verifying names and dates, New Yorker fact-checkers are expected to think for themselves and make complicated editorial judgements. “People who have never been involved in journalism, in fact-checking, think the world is divided into facts and opinions, and the checkers just deal with facts,” says Canby. “For us the bigger complexity is what we think of as fact-based opinions….The way you construct an argument, if there are egregious missing ingredients to it, then it’s something we bring up.”

They all had cell phones. Our fact-checkers would call them up, and they would say, ‘Sorry, we’re in combat. Can you call us back later?’

For each story that goes to print, Canby’s staff will endeavor to speak to every person mentioned, even if they’re not quoted. That includes in stories that take the form of a memoir. As Canby says, “It’s their memory, too.” They give subjects a chance to fix errors, but not rewrite the interview. This can sometimes get contentious for fact-checkers, who might get pushback from Washington power players and business people who are no longer happy with what they said. (Pro tip: Reading back quotes is a surefire way to have a subject ask to rewrite them. Canby gives subjects the substance of what they said, but never reads quotes verbatim.)

Canby describes the fact-check of a recent story by Luke Mogelson about a SWAT team of Iraqis who had suffered at the hands of terrorists, and their efforts to retake Mosul. A staff fact-checker worked in concert with a freelance checker to call the 42 people mentioned in the 17,000-word piece. “They all had cell phones,” says Canby. “Our fact-checkers would call them up, and they would say, Sorry, we’re in combat. Can you call us back later?”

The most extreme checking Canby recalls was for a 30,000-word story by Lawrence Wright about the Church of Scientology, an organization renowned for being extremely litigious. Canby assigned two dedicated fact-checkers to the piece, one of whom spent six months working on it. After the Church of Scientology refused to respond to questions unless they were emailed, the fact-checker compiled a list of 938 questions.

They came one day with 47 binders, four lawyers, and two publicists and we had an all-day showdown.

“They came one day with 47 binders, four lawyers, and two publicists and we had an all-day showdown with the two or three checkers, David [Remnick], our lawyer, their lawyers, and Larry Wright, and Larry’s editor Daniel Zalewski,” says Canby. “We went through the 938 questions, and a lot of them they’d go, ‘right,’ ‘wrong,’ ‘not right,’ which would be not useful. But over the course of the day, enough information was dropped that it put us on to all kinds of other sources, other ideas.”

Not everyone contacted for fact-checking will respond so thoroughly. In recent dealings with the White House, a checker got Hope Hicks to take questions, but then she never responded. In another instance, Steve Bannon replied to a query from a checker with a blank email. That’s not unique to the Trump administration. “One of the checkers who tried to reach Dick Cheney in the early years of the Bush administration walked away from her desk at lunch, and she went back, and she had a voicemail that said, Hi, this is Dick Cheney. That’s it. That’s as far as that one got. So it’s an established pattern.” Nevertheless, Canby says fact-checkers shouldn’t make assumptions. “We think it’s very important, even if you know you’re not going to hear from the White House,” he says, “to act as if you’re going to hear from them.”

Nowadays, Web stories, social media, special projects, and even cartoons get some level of fact-checking treatment. One of Canby’s favorite mistakes ever made in The New Yorker was a cartoon of a penguin sitting on a living room couch and telling its hosts that it preferred to be known as an Arctic-American. “Some biologist wrote in and said, There are no penguins in the Arctic,” he says.

And sometimes the benefits of fact-checking go further than the purpose for which they’re intended. One the great fixes of recent times, according to Canby, was when a fact-checker pointed out to the subject of a story who was planning to get married on the summer solstice, that the date that they had chosen for their wedding was not actually the solstice. They changed the date. Canby says, “That made me very happy.”

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Shelley Hepworth , formerly a CJR Delacorte Fellow, is Technology Editor at The Conversation in Australia. Follow her on Twitter @shelleymiranda.