Philip Roth didn't mince his words when he was asked about Donald Trump. "I found much that was alarming about being a citizen during the tenures of Richard Nixon and George W Bush," the novelist told the New Yorker magazine in January. "But, whatever I may have seen as their limitations of character or intellect, neither was anything like as humanly impoverished as Trump is: ignorant of government, of history, of science, of philosophy, or art, incapable of expressing or recognizing subtlety or nuance, destitute of all decency, and wielding a vocabulary of seventy-seven words that is better called Jerkish than English."

Roth is not alone in thinking that Trump’s limited vocabulary indicates a low intellect and a lack of education. Running the 45th president’s speeches through the Flesch-Kincaid Grade Level assessment, an American readability test, analysts found his vocabulary to be at the level of an average fourth-grader, or nine-year-old, in the US educational system. Mind you, several of his rivals in last year’s Republican primaries were only marginally better.

There is a long tradition in US politics of candidates modulating their language to appear more down to earth, and of world political leaders deliberately dumbing down so as not to appear elitist. Trump, though, is different. His bludgeoning repetition of the same aggressive words – “bad”, “sad”, “failing” – along with a couldn’t-care-less approach to grammar and syntax, point not just to a nine-year-old but to a pretty unpleasant, thuggish one.

The media critic Jack Shafer nailed the Trump rhetorical style during the presidential election campaign. "Flattening the English language whenever he speaks without a script, Trump relies heavily on words such as 'very' and 'great', and the pronouns 'we' and 'I', which is his favourite word. As any news observer can observe, he lives to diminish his foes by calling them 'losers', 'total losers', 'haters', 'dumb', 'idiots', 'morons', 'stupid', 'dummy' and 'disgusting'."

But Shafer cautioned against treating this vocabulary as a marker of low intelligence. “Trump’s professional history indicates a skill at dealing and deceiving, inspiring and selling,” he wrote. “The role Trumpspeak has played in Trump’s surging polls suggests that perhaps too many politicians talk over the public’s head when more should be talking beneath it in the hope of winning elections.”

It’s not just the words Trump uses but the way he puts them together. When the president is speaking without a script – his preferred mode of address – the results can be quite something. When he said in the third presidential debate that Iran should write us a letter of thank you, just like the really stupid – the stupidest deal of all time, a deal that’s going to give Iran absolutely nuclear weapons,” - it may have looked ludicrous on paper, but it resonated verbally with his supporters.

Geoffrey Nunberg, a professor at the University of California, Berkeley, noted in the Los Angeles Times that Trump's repetitions and digressions come off as "spontaneous and genuine" to people listening at a rally. Nonsequiturs aren't troubling if you already get the point. Like most people who attend political rallies, Trump's audience came there to connect, Nunberg said, because "they were already convinced".

When Trump is forced to submit to the teleprompter a quite different rhetorical style comes into play.

"Then, in 2016, the earth shifted beneath our feet," the president told the joint session of Congress in February, describing the triumphant progress of his campaign. "The rebellion started as a quiet protest, spoken by families of all colours and creeds – families who just wanted a fair shot for their children and a fair hearing for their concerns. But then the quiet voices became a loud chorus, as thousands of citizens now spoke out together, from cities small and large, all across our country. Finally, the chorus became an earthquake, and the people turned out by the tens of millions."

Here, presumably under the influence of Steve Bannon and Stephen Miller, Trump appears to be channelling out-takes from the cheesier end of the disaster-movie genre through a filter of blood-and-soil nationalism. It's not pretty – "the chorus became an earthquake"? – but it's not really Trump, either. Tellingly, it's one of the few occasions when the president's behaviour has been hailed as presidential.

As many observers have noted, the effectiveness of Trump’s language is rooted in its unmediated authenticity. Leaving aside the question of how a billionaire who lives in a golden tower with his supermodel wife embodies authenticity, there is no doubt that much of Trump’s appeal resides in the fact that many of his supporters believe he manages to cut through the polished bullshit of mainstream elites to speak, if not from the heart, then at least from the gut. “The secret of success is sincerity. Once you can fake that you’ve got it made.”

The quote has been attributed to many authors, but is it applicable to Donald Trump? Is he faking it? The question is separate from whether he is telling the truth or even whether he knows what the truth means.

Over four decades in the limelight, first as a brash Manhattan property mogul, then as a fixture on the gossip pages, and then as a reality-TV star, Trump always found a way of getting noticed.

At the age of 70 he is unlikely to pretend to be anything other than what he is. Everything is on the surface. Trump has the unusual quality of appearing to be a man with no interior life whatsoever. Crucially, he seems never to have experienced shame.

All of this has allowed him to break some deep-seated American taboos and social conventions. The US is quite a puritanical society, so when Trump says that the country is “going to hell”, or that he doesn’t “give a damn” about various things, or that he’s going to “bomb the shit out of Isis”, he is using language that would have been beyond the pale for most of his predecessors.

For Trump’s supporters, however, the language marks him as the disruptive agent of change they were searching for. The same may even be true of the “grab them by the p***y” tape, which many wrongly thought would put an end to his electoral chances.

And then there’s Twitter. It is hard to conceive of a communications tool better suited to Donald Trump’s strengths. The brevity enforced by the platform’s 140-character limit means he is forced to condense and distil in a way that never happens when he speaks. The use of hashtags has allowed him to elevate playground insults – #littleMarco, #crookedHillary – into viral memes retweeted by millions.

Now, with White House mouthpieces jousting with journalists over whether the president's use of quote marks – he's getting fonder of them all the time – means he shouldn't be taken literally, it is hard to avoid the conclusion that we're all being dragged into a hall of mirrors, one where every banal word, casual insult or blatant untruth is to be parsed for meaning.

What should be clear by now is that, when it comes to Trump’s language, there is no meaning beyond the shallowest.