THE imprisonment of David Irving for Holocaust denial raises an important question: to what extent does truth need the protection of law? The particular case is highly specific to Austria, whose people felt that the force of law was needed if the past was to be confronted honestly and Nazism placed beyond the limits of acceptable speech. I for one would not wish to second-guess the decision of a country painfully wrestling with its past.

On the more general issue, though, there is a chapter in the history of ideas that deserves to be better known. One of the achievements of early Islam was to rescue the works of Plato, Aristotle and their disciples from oblivion. A key figure in this was the philosopher Ibn Rushd (1126-98), known in the West as Averroës, who made a powerful case for freedom of speech in pursuit of the truth. You should always, he said, cite the views of your opponents. Silencing them is an implicit admission of the weakness of your case.

Rabbi Judah Loewe (1525- 1609), the Jewish sage known as the Maharal of Prague, cites Averroës while making the same point. He adds: “Do not say to your opponent: ‘Speak not, close your mouth.’ If that happens, there will take place no purification of religion . . . This is the opposite of what some people think, namely, that when you prevent someone from speaking against religion, that strengthens religion. That is not so, because curbing the words of an opponent in religious matters is nothing but the curbing and enfeebling of religion itself.”

Within a century John Milton made the same point in his pamphlet in defence of free speech, Areopagitica (1644): “And though all the winds of doctrine were let loose to play upon the earth, so Truth be in the field, we do injuriously by licensing and prohibiting, to misdoubt her strength. Let her and Falsehood grapple; who ever knew Truth put to the worse, in a free and open encounter?”

John Stuart Mill reiterated the argument in On Liberty (1859): “But the peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.”

I find it moving to trace this conversation, extended across seven centuries, in which first a Muslim, then a Jew, then a Christian, then a secular humanist, come together to agree on the importance of free speech and the dignity of dissent. Truth, they believed, is not served by erecting around it defensive walls of legislation. We honour it by surrounding it with spacious lawns of free expression and flowerbeds of respectful debate.

Their view did not always prevail. To this day, religion is seen in a negative light because at times it chose the other way: to impose truth by force. The result in the Middle Ages was a series of staged disputations, forced conversions, excommunications, inquisitions and burnings at the stake. Nothing was served by this: not religion or truth, not freedom or human dignity. It remains a stain on the record of faith.

That Europe eventually found its way to freedom was due in no small measure to the wisdom and courage of figures such as Averroës and Rabbi Loewe, Milton and Mill. They believed that truth is strong enough to defeat its opponents without the help of law, coercion or intimidation. They had the confidence born of faith. Their opponents had the aggression born of fear.

In an age when religion is again in danger of becoming a repressive force, their story is worth retelling. There was a time when Muslim, Jewish, Christian and humanist voices joined in defending free expression as a matter of religious and moral principle. We may yet need them to do so again.

Rabbi Sir Jonathan Sacks is the Chief Rabbi of the United Hebrew Congregations of the Commonwealth