On Friday, France is marking 100 years since the separation of Church and State. With Islam on the rise in the restive suburbs, French-style secularism is being questioned. Concluding a series on French Muslims, Henri Astier asks whether it can remain a core value of the Republic.
To outside observers, French secular laws can work in mysterious ways.
Muslims are raising funds for new mosques all over France
Consider the country's top two religions. One, bringing together six million faithful, is thriving: converts are joining all the time and prayer halls are springing up.
The other is languishing. The number of preachers has halved in 40 years. With dwindling congregations, places of worship are inexorably closing down.
Yet no public money can go to the first, while millions of euros are spent every year on maintaining buildings the second no longer needs.
The reason is that under the 100-year-old law that founded modern French secularism, the state offered to take over the churches' existing buildings, while cutting all others' ties.
The French Catholic Church - the foundering religion described above - eagerly accepted the offer. Islam - the new, thriving faith - was not there to do so.
Many conclude that the 1905 law is in serious need of updating.
Second largest religion
Five million Muslims (estimate)
1,600 places of worship
35% Algerian origin (estimate)
25% Moroccan origin (estimate)
10% Tunisian origin (estimate)
Concentrated in poor suburbs of Paris, Lille, Lyon, Marseille and other cities
"It should be revised to allow the central government or local authorities to contribute to the construction and the upkeep of mosques or pagodas," Manuel Valls, an MP for the socialist party, told the BBC News website.
Mr Valls, who has written a book entitled La Laicite en face (Looking Secularism in the Face), says such a revision would be only fair.
Above all, it would help counter what he views as a real threat to the Republic: meddling by outsiders from Saudi Arabia and other Muslim countries.
"A change [in the 1905 law] would prevent mosques being financed by foreign powers - notably the Wahhabi kingdom," Mr Valls says.
The socialist MP is not alone. Calls to amend the law on the separation of Church and State are getting louder, and transcend party politics.
Interior Minister Nicolas Sarkozy, a popular conservative, supports reform for much the same reasons as Mr Valls.
But French secularism has deep roots, going back to the 1789 revolution, and any move to chip away at a cornerstone of the Republic will meet stiff resistance.
National Assembly Speaker Jean-Louis Debre, for instance, is one of those who oppose changing the legislation.
"Let us not reopen French civil wars," he recently told the Figaro newspaper.
Muslims leaders say Islam must accept France, not vice versa
Traditionalists like Mr Debre remain very much in the majority - both on the political right and on the left.
Their strength was highlighted last year, when parliament approved a ban on religious signs in French public schools. The legislation mentioned no faith in particular, but its clear target was the Islamic headscarf.
Every single party represented in the National Assembly voted in favour.
Secularism remains an article of faith in France. Even religious groups are careful not to confront it head on. Muslims may oppose the 2004 ban, but not the 1905 law - pointing out that secularist France lived happily for 99 years without a headscarf ban.
"We have no problem with secularism," says Lhaj Thami Breze, president of the Union of Islamic Organisations of France (UOIF).
"Islam must adapt to France, not France to Islam."
The traditionalist retort is that such opinions voiced by all Muslim leaders are a smokescreen.
Political Islam, they argue, is in the ascendant, and represents the biggest challenge to France's secularist tradition since the 19th Century.
The widespread feeling that the theocratic party is rearing its ugly head again in the form of Muslim radicalism explains why the headscarf ban is so popular in France.
A number of prominent Muslims share these concerns, such as Tunisian-born writer Abdelwahab Meddeb.
"The radicals view Islam as the future of the world and the West as the enemy," Mr Meddeb, author of Islam and its Discontents, told the BBC News website.
"The UOIF is part and parcel of this view. They must not be banned, but watched and challenged at every turn."
To most Muslims, however, such concerns are unwarranted.
"A hundred years ago the context was totally different," says Sofiane Meziani, a student from Lille. "The state was battling a powerful Church."
Replaying the 1905 battle today makes no sense, he argues: "Islam has no power in France. So there is no confrontation between Islam and secularism."
The idea that France's secular tradition is not under threat is also central to the reformers' case: changes to the 1905 law, they contend, will not lead to its unravelling.
Mr Valls and others note that it has been amended many times and that it is flexible.
Alsace, which was not part of France in 1905, is under a German-style system that allows public funding of churches.
Adaptation is needed, reformers argue, for simple reasons of pragmatism and honesty.
Mr Valls, who is also mayor of a town with a large immigrant community, has to make decisions involving religion.
He regularly meets religious leaders, and has to rule on issues such as a Muslim section in the cemetery or ensuring that ritual slaughter of animals during festivals is carried out properly.
At the moment he is constrained by legislation and occasionally resorts to "subterfuges to get around it" - such as pretending that a new pagoda is really a museum so he can help finance it.
"Such hypocrisy is wrong," he says. "France should stop pretending the state will have nothing to do with religion and revise the 1905 law to include religions that have arisen in the past century."
Change in the end may come, but Mr Valls and his fellow reformers will have to fight every inch of the way.
Other features in Henri Astier's series on French Muslims: