As dons at Cambridge vote on a new protocol on constraints to free speech, we mark this month the 500th anniversary of the public burning of Martin Luther’s books outside the west door of Great St Mary’s, the university church at Cambridge.

After the 1517 publication of his famous 95 Theses, raging against the Church’s sale of ‘indulgences’ that purported to pardon sin in exchange for money, Luther had been denounced by Pope Leo X in a papal Bull. This accused him of (among other things) saying things that were ‘offensive to pious ears’. Luther then burned the papal Bull on 10 December 1520, giving further offence. He was excommunicated the following year.

Make no bones about it: Martin Luther intended to offend. He was not just advancing a reasoned case against Catholic practice — though he did — but also turning his protest into a campaign that would catch fire. It would have been entirely possible for the professor of moral theology at the University of Wittenberg to have made his arguments with quiet courtesy, ruffling a few episcopal feathers but attracting no public interest. But he wanted to stir things up.

Luther could (in the language now recommended to Cambridge dons 500 years later) have worded his case with ‘respect’ towards opponents. The Wittenberg professor made no such concession. His language is neither respectful nor polite, nor even tolerant. In Thesis 10 he accused priests of acting ‘ignorantly and wickedly’. In his 28th thesis he accused priests who sold indulgences of ‘greed and avarice’.Thesis 32 claims that such priests face eternal damnation. Attempting to buy divine pardon for money (he says in Thesis 45) will earn ‘God’s wrath’. They are ‘the enemies of Christ’, he adds in Thesis 53. ‘Let him who speaks against [my] truth concerning papal indulgences’ (Thesis 71) ‘be anathema and accursed’. Luther goes on (Thesis 72) to accuse these preachers of ‘lust and licence’. To believe their priestly teachings (Thesis 75) ‘is madness’.

And so on. No need to labour the point. This was a man intent on disrespect. By insulting church practice, by (indirectly) implicating the Pope, and by lashing out against not just a theological claim, but against the virtue, good faith and probity of those priests who made it, the aim was to insult, incite and outrage. He meant to provoke churchmen who took a different view. The fury he sparked was not a collateral consequence of the argument he made, it was central to his purpose. Luther was not even ‘tolerant’ (the word preferred by the dons campaigning against the censorship that ‘respectful’ implies). He was angry. Angry not only with an idea, but with the individuals who promoted it. He meant to wound them personally.

Was this simply because Luther was vindictive by nature? Absolutely not. We’ve no window into his nature, but it is plain to scholars of his era that he had wanted to start a popular movement for reform. Hence his fiery language, his personal indictments, his burning of the Papal Bull. This was a man with a strong argument, passionately held, and a canny sense of how to set his cause alight. By his intemperate, intolerant, dis-respectful language, Martin Luther lit the fuse that led to a conflagration in European theology: the Reformation was surely one of the most significant events in the history of our continent. And it began, as it had to, with language that in the words of the Pope was ‘offensive to pious ears’.

The battle of ideas, were it no more than a battle of ideas, could perhaps have been conducted throughout human history with unfailing respect, tolerance and civility. On a more cerebral planet, no voice might ever need to be raised. But on this planet battles of ideas are shot through — you may even say ‘polluted’ — by other forces, other motives, other power struggles. Sometimes the ideas are little more than hostages, proxies, in deeper and more covert battles. Sometimes the ideas do matter, but they come bearing weapons that are not intellectual.

Prominent among what can contaminate a superficially simple battle of ideas is the issue of authority. For centuries the Church was able to frighten and coerce and (more insidiously) command a kind of awe that discouraged even private dissent or question. I sense that among many of its followers Islam still does the same today. Among Jewish denominations, the ultra-Orthodox seem to exert this power over followers. Unthinking deference to Catholic teaching is fading, but still evident in parts of the world.

A dominating religion is but one example of doctrinal authority that may not at first be easy to confront head-on. But it can be twitted. Insult and abuse, personal invective, scorn and ridicule are vastly important among the means of obliquely challenging a ruling dispensation, and loosening its command around the edges. Voltaire knew that. John Wilkes too. Likewise (say) Christopher Hitchens. Rob these men — or rob today’s leading cartoonists — of their impudence and you rob them of their agency.

Allied to authority is intimidation. In ages like ours, certain dominating ideas can exert a similar power to chill potential dissent through something close to fear. The wilder extreme of the ‘trans’ movement (and I do mean movement, not trans people, for whose thoughts and feelings nobody can be spokesman) has had success through social media in frightening off all but the brave from publicly questioning some of its claims. One of the ways it does this is through the passive-aggressive means of taking offence — like the ‘pious ears’ offended by Luther. But if we are to challenge folly we must needs offend it: challenge will be taken as disrespect, discourtesy, ‘intolerance’. So be it.

We who believe in free speech will probably win the battle for the right not to ‘respect’ some opinions or those who hold them. But let’s not settle for compromises like ‘tolerance’ or ‘courtesy’. Luther showed neither. Had he had better manners, we’d never have heard of him.