On the streets of Istanbul, Muslim girls march in defiance of the Turkish state. They are demanding the right to wear a headscarf when they go to school. I don't feel I have to comply with what the state says. This is my faith - and I want to live by my faith.

Zeliha

In most countries, the issue would be trivial, but not here. In Turkey the official orthodoxy of the state is Kemalism - the secular nationalism introduced by Turkey's founding father, Mustafa Kemal Ataturk, when he created the modern state in the 1920s.

But, although the state is secular, the people are overwhelmingly Muslim. So the headscarf has become a highly charged symbol of the collision between Kemalism and Islam.

Seventeen-year-old Zeliha was turned away by riot police when she tried to go to school in her headscarf. So why does she not simply obey the state and leave the headscarf at home?

"I don't feel I have to comply with what the state says. This is my faith - and I want to live by my faith,"  Zeliha said.

Vibrant and secular

So how should we understand the headscarf affair? What does it tell us about modern Turkey?  They're using the headscarf as a provocation. They're politicising the whole thing - and the Turkish people are not comfortable with that

Sabri Yirmibesoglu, retired general:

In many ways, Turkey is a vibrantly modern and secular country where Ataturk's legacy appears, on one level, to be alive and well. The guardians of that legacy - the high priests of Kemalism - are the Turkish generals.

Sabri Yirmibesoglu, himself a retired general, defends the view that it is wrong for women to wear headscarves in government schools or in government departments.

"In Turkey it is not forbidden to cover your hair or your body. But the Turkish public gets upset when this is done in the public sphere - and in public education - and when the headscarf is used as a political symbol."

Fighting radical Islam

Secularism, though, is not confined to the Turkish military. Mehmet Ali Birand is one of Turkey's best-known liberal commentators.

So doesn't he believe that girls like Zeliha have a point when they claim the democratic right to wear a headscarf?

The issue of headscarves has become the focus of the secular-Islamic struggle.

"Well, she had a point before 11 September. But I don't think that she has as strong a point as before. There is a fight between moderate Islam and radical Islam.

"The fight is not between the United States, and it is not between the Christian world or the Western world and Islamic countries. No, this war is within us," Mehmet Ali Birand said.

To understand why the headscarf issue exercises such passions, it is necessary to look back at the beginnings of modernity in Turkey.

These origins precede Ataturk and his secular nationalism and go back, in fact, to the period of the Tanzimat - the reforms introduced by the Turkish sultans in the middle of the 19th century.

These sultans realised that Europe had outstripped the Muslim world in military power and scientific achievement.

In response, they began to overhaul the ramshackle bureaucracy of the Ottoman Empire and modernise the education system.

The reforms also achieved something lasting which would change the face of Turkey once and for all and create profound social and political divisions.

Islamic revival

But, even if Ataturk owed a debt - an unacknowledged debt - to the reforming sultans, there is no doubt that the reforms introduced in the 1920s and 1930s were far more radical than anything that had gone before.

Mustafa Kemal Ataturk founded Turkey as a secular, western leaning state

He changed the way Turks dress, the language they spoke, he gave women the vote and, above all, he pushed religion to the sidelines, most notably in the field of education.

But then came the Islamic revival in Turkey, which found its political expression in the 1970s and 1980s with the emergence of the Refah - or Welfare - party.

It began as an urban working class movement and then grew to affect a group of people the Kemalists had always seen as theirs - the middle class.

Kemalists began to panic.

The Refah party - and its leader Necmettin Erbakan - built up support because Turks were fed up with the mainstream parties of left and right, which they saw as corrupt and self-seeking.

Cutting Islamists to size

In 1996 Erbakan became the country's first Islamist prime minister. For the Kemalists, it was an earthquake. But Erbakan overplayed his hand and, after only a year in office, he was pushed out as a result of sustained pressure from the generals.

The Islamists want the very young children to be educated... with a tremendous amount of hatred against whatever looks European, looks secular.

The crackdown did not stop there. The authorities have done their utmost to cut the Islamists down to size.But their critics are not convinced by their new-found moderation.

Nur Vergin, professor of sociology at Istanbul University, thinks it is purely tactical. She believes that if the Islamist groups are left unchecked, they will poison the minds of the 8,000 boys and girls at Istanbul's Islamic schools.

"What does the religious teacher teach them? I'll tell you what, because I have examples. For example, a girl of nine, born in Istanbul - her parents have the means of sending her to school, but she doesn't know how to read - she cannot read yet.

"But she knows that, if you put nail polish on your nails, you'll go directly to hell. This is very serious. They want the very young children to be educated in that direction - with a tremendous amount of hatred against whatever looks like European, looks like secular. Little Taleban, you know," Nur Vergin said.

That word. Taleban, is a sign of just how polarised this country has become. Islamists and Kemalists are not just hostile to one another - each feels deeply threatened by the other.

Issue of identity

So has this polarisation reached the point of an identity crisis? Students at Istanbul University have mixed views.

"Turkey doesn't have an identity crisis. A minority group, a small group of people, are living in line with the principles of Islam. But the majority of the Turkish people are Western-oriented, and they have a Western education," one student said.

Another student said "Yes, I do think that there is an identity problem in Turkish society, which comes from the educational system, giving us the Eastern values on the one hand, and on the other hand, the same education system is giving us the Western values. So it's mixed up."

Three quarters of a century after the founding of the modern state, Turks have grown used to Kemalism.  But many - perhaps most - consider that Islam is part of who they are.

For now, the Kemalist model of modernity is dominant - not because everyone accepts it - but because the elite which does has managed to impose it on those who do not.

But can that continue indefinitely?

Since Ataturk's death, his brand of secularism has come under periodic challenge. Many say there is no reason to believe it won't come under challenge again.