The single most striking fact about the list of famous people who have appeared at the Oxford Union down the years - the only striking fact, really - is that it is a list of famous people. Beyond that, the list appears to obey no logic, no organising principle. In parts, it reads as if the 184-year-old university debating society were a truly significant international political forum, but then just when you think you detect some kind of pattern (Ronald Reagan, Richard Nixon, Yasser Arafat, Pervez Musharraf), someone will crop up to confound it (Michael Winner).
The Union combines a nearly unique global stature with the priorities you might expect from any group of students in their late teens and early 20s, and, as a result, strange juxtapositions ensue: on any given evening, His Holiness the Dalai Lama might be visiting - but then again, so might Johnny Ball or Westlife.
A month before Monday night's nationally controversial debate on free speech - which saw the debating chamber invaded by demonstrators protesting at the inclusion of the Holocaust denier David Irving and Nick Griffin, chairman of the British National Party - the Union's featured event was a secondhand bike sale. And yet the Griffin/Irving debacle was featured on almost every TV news bulletin and, yesterday, in almost every national newspaper; one even dedicated the whole of its first three pages to the event.
It was the latest in a string of reminders of the Union's strangely unclear status: an institution that celebrities of all kinds, including world leaders, are flattered to be asked to visit, and yet, simultaneously, a vaguely preposterous black-tie social club not taken particularly seriously even by most Oxford students. A vintage example of this dissonance occurred earlier this year, after the academic Norman Finkelstein was disinvited from a debate on the Middle East in circumstances that remain almost completely baffling. (All that is certain is that the debate was poorly conceived, with Finkelstein, a vocal critic of Israel, debating against three other vocal critics of Israel.) The hawkish American law professor Alan Dershowitz, livid that Finkelstein had been invited in the first place, inserted himself into the affair, writing a thundering editorial in the Jerusalem Post. "This is an obituary for the Oxford Union," he wrote, portentously, "which claims to be one of the most famous and distinguished debating societies in the world [but] has become a propaganda platform for extremist views, primarily of the hard left."
You might agree with this statement; you might disagree with it. But either way, you might be moved to observe that it was odd for Dershowitz to be writing in the Jerusalem Post in such momentous terms about an institution that, a few years previously, had played host to Kermit the Frog.
The truth is that the Oxford Union does not figure very prominently in the life of the average Oxford undergraduate. A majority of students join it when they arrive at the university, but the majority of those rarely attend. "A very small and largely deranged minority run the place, and think it's all hugely important," argues one former editor of the Oxford Student newspaper, who asks not to be named. "I suppose the wider world is forced to care because there are sometimes interesting speakers, who sometimes say interesting or incendiary things, lulled into a false sense of security by the old boys' club atmosphere, and the vast quantities of wine they're fed before they speak."
But if most students care little about the Union (it isn't a students' union in the sense that this is meant at other universities - Oxford has one of those, too), the rest of the world certainly does, and always has done. The Union's outsized role in British national life was never more in evidence than on the famous night of February 9, 1933, when students voted 275 to 153 in favour of the motion "that this house will in no circumstances fight for its King and Country". Hitler had become chancellor of Germany just 10 days earlier, and the vote provoked uproar. "There is no question but that the woozy-minded communists, the practical jokers, and the sexual indeterminates of Oxford have scored a great success in the publicity that has followed this victory," roared the Daily Express. Churchill called it an "abject, squalid, shameless avowal", and some historians argue that it exerted a significant influence on Hitler's assessment of the British population's willingness to fight. The row blew over quickly in Britain, the Israeli commentator Amnon Rubinstein has observed - "one of many manifestations of civic and democratic society in action. But Hitler, totally unfamiliar with the vagaries of free societies, attached great significance to that silly vote, and saw it as another proof that the democracies were weak, decadent, and lacking the will to fight the might of Nazi Germany."
The Union was still being taken extremely seriously 50 years later when Andrew Sullivan, now a US-based blogger and columnist, was its president. Aged 19, Sullivan managed to persuade the American defence secretary Caspar Weinberger to debate against the historian and leading anti-nuclear campaigner EP Thompson - only to have the Thatcher government persuade Weinberger to pull out. ("I was pissed [off], but what could I do?" Sullivan later said. "I was pro-Thatcher, but I was equally pro-debate.")
And there are still plenty of people willing to argue for the Union's ongoing relevance today. "Some people suggest it's an elitist talking shop for which there's no room in the modern educational system, and the answer to that is no," insists Alan Duncan, the conservative MP and shadow secretary of state for business. "The other question is whether the nature of political discourse is changing such that it's now so shallow and media-driven that debate about philosophical issues hardly ever takes place. That's partly true, but that doesn't mean the Union has no purpose - it's thriving, not struggling, in that climate."
When Duncan was 18 and involved in the Union, shortly before he became its president, he met the British fascist leader Oswald Mosley. "I didn't know much about him. I met him, and I started to understand. Some on the fascist left might say I should never have met him," he adds, addressing this week's controversy, "but if I hadn't, my education would have been the poorer. Education is about teaching people how to think, not teaching them what to think, and I don't think the mob should have the right to insist that students should have to adopt hand-me-down opinions."
The expansion of higher education and the gradually diminishing role of Oxbridge in British national life might prompt the thought that the Union, these days, is living on little more than its historical reputation. (For a demonstration of the awkwardness its members have sometimes displayed in trying to adapt to the 21st century, readers with a taste for schadenfreude are invited to search YouTube for clips of the hip-hop artist Dizzee Rascal performing there live last year.)
But this week's scenes outside the Union's 19th-century redbrick buildings, not to mention the intense media coverage, could hardly be ignored. Whatever myth about the Union the debaters and demonstrators were in thrall to on Monday night, it was the same myth that had drawn everyone from Desmond Tutu to Diego Maradona to Jerry Falwell to Michael Jackson, surreally, in 2001 - a myth sufficiently that is sufficiently powerful to have become a self-fulfilling prophecy: the Oxford Union matters because the Oxford Union matters.
The 1933 King and Country motion might not quite have sparked the second world war, but if you squint, you can almost see in Alan Duncan's presidency of the debating society evidence of the Union precipitating at least one British political earthquake. "We had a televised debate on devolution for Scotland and Wales, the Sunday before the referendums were held, which ended up bringing down the Callaghan government," he says. "The Union's debate was the most cogent, well-watched forum on the issue. I'm not quite claiming that I single-handedly brought down Callaghan and brought in Margaret Thatcher. But it was my part in his downfall".