Why do some people refer to themselves in the third person?

Republican presidential candidate Donald Trump quite often refers to himself as "Trump" - instead of using the words "I" or "me". It's an eccentric habit that delights his critics, though he's just the latest in a long line of politicians to talk this way. What does it say about him?

"Nobody would be tougher on Isis than Donald Trump," the billionaire property mogul said when he announced his 2016 presidential bid.

"You wouldn't even be hearing about immigration if it weren't for Donald Trump," he told NBC, claiming that other presidential contenders would not have been bold enough to mention the subject if he had not led the way.

"Trump was able to get something. I don't know what the hell it was, but it doesn't matter. Because I'm off that subject," he said in an interview with CNN last month, referring to President Obama's decision to release his birth certificate in 2011. (Trump and other "birthers" had voiced doubts that Obama was born in the US - a precondition for becoming president.)

It's not a new habit. In 2009, Trump said that year's Miss Universe finalists were more beautiful than in previous years, adding: "In the old days, you got what you got. Now, Trump picks them. It makes a big difference."

In fact, he's so renowned for using the third person that collections of Trump quotations often quote him as saying: "Love him or hate him, Trump is a man who is certain about what he wants and sets out to get it, no holds barred. Women find his power almost as much of a turn-on as his money." In reality though, these are not his words, but words used by the author Marian Salzman when she listed him in 2005 as a top 10 "ubersexual".

Trump's critics mock him mercilessly for this habit.

"Weird the @realDonaldTrump refers to himself in the third person. Not just voters who see him as an out of body experience. #DonaldTrump," says @SandraEckersley.

"How adorable that Donald Trump continues to refer to himself in the third person. Kinda like Kanye West. And Gollum," says @ChandiB, in a reference to a sinister creature in JRR Tolkien's The Hobbit.

Business Insider's Nicholas Carlson drew attention in 2012 to a tweet in which Trump wrote "congratulations Donald!" as he celebrated the success of the Apprentice - a reality TV show in which he sets contestants competing for a job in his company a range of challenges.

"What kind of person refers to himself in the third-person? What kind of person would congratulate himself?" wrote Carlson.

"But then you remember that the answer to both those questions is: a kind of person like Donald Trump."

Curiously, Trump is not the only candidate in this election to use the third person about himself. Bernie Sanders, the 73-year-old left-winger bidding for the Democratic nomination, is another.

His Twitter feed is full of tweets announcing what "Senator Sanders" has been or will be doing. This usually appears to be a case of a press officer using his account, but has provoked some puzzled responses.

A recent Sanders interview on NPR, in which he said, "Bernie Sanders gets very, very nervous when he hears Republicans, who apparently just can't get enough of war" also prompted some criticism.

"Speaking of self in third person is a bit troubling. Suggests exaggerated sense of self, or English royalty. Which is he?" tweeted @PHLoving.

But many of those who commented may have been unaware that the interviewer had asked what "President Bernie Sanders" would do, making an answer in the third person quite natural.

It's "pretty rare" for Sanders to speak this way, according to Neal Goswami, head of the Vermont Press Bureau.

"I have heard him reply to the odd question from reporters by saying something like 'Bernie Sanders doesn't say that' - but I've never heard it in a speech or when he's talking to voters," he says.

For some this will trigger a sense of deja vu. Twenty years ago Bob Dole was pilloried for the same third-person habit as he ran against Bill Clinton.

"If you had to leave your children with Bob Dole or Bill Clinton, I think you'd probably leave them with Bob Dole," was one example that led to jokes on Saturday Night Live.

Bob Dole ran against Bill Clinton in the 1996 US presidential election

"Bob Dole Needs to Put the 'I' in Identity," was the headline of one column in the LA Times. The columnist, Scott Harris, quoted a pundit who noted that "Bob Dole always refers to himself in the third person, as if he's someplace else."

The technical term for it is illeism from "ille", the Latin for "he", and history provides many examples, from Julius Caesar - who wrote a history of his Gallic campaigns as if he were an objective observer rather than a protagonist - to Charles de Gaulle and Richard Nixon, basketball megastar Le Bron James and Mikhail Gorbachev. In Gorbachev's case it was one of the linguistic habits that led his rival, Yegor Ligachev, to say he was behaving like an "enlightened monarch".

Sesame Street's Elmo was another fan

Toddlers are often illeists, before they fully grasp the use of "I" and "me", so fictional characters portrayed as young children or simple-minded adults sometimes speak like this. Examples include Sesame Street's Elmo and Jimmy from the sitcom, Seinfeld.

But why would someone like Trump or Sanders become an illeist?

Psychotherapist Kim Schneiderman, author of Step Out of Your Story: Writing Exercises to Reframe and Transform Your Life, says thinking about yourself in the third person has been shown to be healthy, and something that many successful people do naturally. What's less normal is going from thinking to talking about yourself in the third person.

"Bernie Sanders and Donald Trump are both very successful, confident individuals - though in very different ways. Their confidence might explain why they would be comfortable outwardly referring to themselves this way," says Schneiderman.

"Also, people in the public eye are performers and thus develop personas. If Trump and Sanders speak about themselves in the third person, perhaps they are actually speaking about their personas."

In Trump's case, he is also a brand.

"This is a man who has his picture up on his walls and his name plastered on the tallest buildings in Manhattan.

"Trump talking about himself in the third person reflects his perception of himself as being a larger-than-life character in the world stage," suggests Schneiderman. "Which, aside from the fact that he has an inflated ego, he happens to be."

Elizabeth Ossoff, an expert in political communication at St Anselm College, also sees Trump as a special case, partly because he is so prolific in his use of the third person.

But her advice to politicians is not to overuse the technique, as in her view people tend to find it "off-putting", and un-presidential.

"The use of the third person creates an unwelcome distance. We Americans want our presidents to be regular people but not too regular. We still put them up on a pedestal but want them to be humble about it since we put them in office. It's an odd contradiction at times," she says.

It can't be all that off-putting though. Trump and Sanders are still doing pretty well in the polls.

Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.