The anti-caricature campaign started by attacking a newspaper. It then focussed on Denmark as a defender of the freedom of the press, and now it has all of Europe in its sights, which it accuses of having a double standard. The European Union allows the Prophet to be denigrated with impunity, but it forbids and condemns other "opinions" like Nazism and denial of the Holocaust. Why are jokes about Muhammad permitted, but not those about the genocide of the Jews? This was the rallying call of fundamentalists before they initiated a competition for Auschwitz cartoons. Fair's fair: either everything should be allowed in the name of the freedom of expression, or we should censor that which shocks both parties. Many people who defend the right to caricature feel trapped. Will they publish drawings about the gas chambers in the name of freedom of expression?

Offence for offence? Infringement for infringement? Can the negation of Auschwitz be put on a par with the desecration of Muhammad? This is where two philosophies clash. The one says yes, these are equivalent "beliefs" which have been equally scorned. There is no difference between factual truth and professed faith; the conviction that the genocide took place and the certitude that Muhammad was illuminated by Archangel Gabriel are on a par. The others say no, the reality of the death camps is a matter of historical fact, whereas the sacredness of the prophets is a matter of personal belief.

This distinction between fact and belief is at the heart of Western thought. Aristotle distinguished between indicative discourse on the one hand, which could be used to reach an affirmation or a negation, and prayer on the other. Prayers are not a matter for discussion, because they do not state: they implore, promise, vow and declare. They do not relate information, they perform an act. When the Islamist fanatic affirms that Europeans practise the "religion of the Shoah" while he practises that of Muhammad, he abolishes the distinction between fact and belief. For him there are only beliefs, and so it follows that Europe will favour its own.

Civilised discourse analyses and defines scientific truths, historic truths and matters of fact relating to knowledge, not to faith. And it does this irrespective of race or confession. We may believe these facts are profane or undignified, yet they remain distinct from religious truths. Our planet is not in the grips of a clash of civilisations or cultures. It is the battleground of a decisive struggle between two ways of thinking. There are those who declare that there are no facts, but only interpretations - so many acts of faith. These either tend toward fanaticism ("I am the truth") or they fall into nihilism ("nothing is true, nothing is false"). Opposing them are those who advocate free discussion with a view to distinguishing between true and false, those for whom political and scientific matters – or simple judgement – can be settled on the basis of worldly facts, independently of arbitrary pre-established opinions.

A totalitarian way of thinking loathes to be gainsaid. It affirms dogmatically, and waves the little red, or black, or green book. It is obscurantist, blending politics and religion. Anti-totalitarian thinking, by contrast, takes facts for what they are and acknowledges even the most hideous of them, those one would prefer to keep hidden out of fear or for the sake of utility. Bringing the gulag to light made it possible to criticise and ultimately reject "actually existing socialism". Confronting the Nazi abominations and opening the extermination camps converted Europe to democracy after 1945. Refusing to face the cruellest historical facts, on the other hand, heralds the return of cruelty. Whether the Islamists - who are far from representing all Muslims – like it or not, there is no common measure between negating known facts and criticising any one of the beliefs which every European has the right to practice or poke fun at.

For centuries, Jupiter and Christ, Jehovah and Allah have had to put up with many a joke. The Jews are past masters at criticising Yaweh – they've even made it a bit of a speciality. That does not prevent the true believers of any confession from believing, or from respecting those of a different faith. That is the price of religious peace. But joking about gas chambers, raped women and disembowelled babies, sanctifying televised beheadings and human bombs all point to an unbearable future.

It is high time that the democrats regained their spirit, and that the constitutional states remembered their principles. With solemnity and solidarity they must recall that one, two or three religions, four or five ideologies may in no way decide what citizens can do or think. What is at stake here is not only the freedom of the press, but also the permission to call a spade a spade and a gas chamber an abomination, regardless of our beliefs. What is at stake is the basis of all morality: here on earth the respect due to each individual starts with the recognition and rejection of the most flagrant examples of inhumanity.

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The article was originally published in French in Le Monde and in German on Perlentaucher on March 3, 2006.

André Glucksmann is a French philosopher who was active in the protest movement of the 1960s and opposed the communist regimes of Eastern Europe. His most recent book, "Le Discours de la Haine" (The discourse of hatred) recently appeared in German as "Hass".

Translation: jab.