The argument in Nomad, a thought-provoking but ultimately frustrating book, is simple: Muslims need to be emancipated from Islam. While some argue that the faith needs to undergo a process analogous to the Reformation, Ayaan Hirsi Ali's position is far more challenging. She argues that Islam is simply incapable of genuine reform. Hirsi Ali accuses western multiculturalists of assuming that Muslims cannot evolve. Her own idea of evolution, however, is simply for them to stop being Muslims.

Given her extraordinary life, the simplicity of these ideas is rather disappointing. Her previous book, Infidel, told the story of her childhood in Somalia, her crisis of faith after the 11 September 2001 attacks and her brief career as a Dutch politician. In 2006, she left the Netherlands for good after Rita Verdonk, a colleague of hers in the liberal-conservative VVD party, tried to strip her of her Dutch citizenship and in doing so brought down the centre-right coalition government in which the VVD was a partner.

Nomad, on the other hand, is a slightly disjointed mixture of memoir and polemic. Hirsi Ali describes her new life in America (she now works for the American Enterprise Institute in Washington, DC), and, in a series of intensely moving chapters, her attempts to reconnect with members of her family after the death of her father in 2008. She also uses her own experiences to make a probing critique of Islam - hence the book's subtitle, A Personal Journey through the Clash of Civilisations.

Unlike the American writer Paul Berman, who argues that Islamism is in part a product of the influence of 20th-century western extremist movements, and thus rejects Samuel P Huntington's idea of a "clash of civilisations", Hirsi Ali sees the west and the Muslim world as simple binary opposites. She is imprecise in the way she talks about both.

For example, she makes few distinctions between Holland and the United States, even though the Dutch relationship between religion and the state is quite different from the American. And she somewhat simplistically identifies the west with modernity and sees her life story as a journey through time as well as space. Islam, however, becomes a kind of anachronism that is diametrically opposed to reason.

For Hirsi Ali, the real problem with Islam is not so much the specific verses in the Quran which, for example, encourage violence against women (though she does criticise these), but the status of the entire text as the word of God, and therefore infallible. "Many Muslims do not actually obey every one of the Quran's many strictures, but they believe that they should," she writes. She argues that, unlike the Bible, the Quran has a "read-only lock", which means that believers cannot engage with it critically and thus makes Muslims vulnerable to indoctrination by fundamentalists. To her, therefore, Islam and the Enlightenment are completely incompatible.

Hirsi Ali frequently invokes the Enlightenment, but never fully explains what she means by it. In fact, she is so wide-eyed about the Enlightenment that it sometimes feels as if Hirsi Ali - who celebrates modernity - were writing in the 18th century rather than the 21st. Her position on Islam is as blunt as the stance on Judaism expressed by Stanislas de Clermont-Tonnerre in the French Constituent Assembly in 1791: "One must refuse everything to the Jews as a nation, and give everything to the Jews as individuals."

There is one brief moment in Nomad when she seems, fleetingly, to see the possibility of a compromise between Islam and modernity after all. It comes as she describes her experiences speaking to students on college campuses in the United States. She says that the auditoriums in which she speaks are often filled with "clever young Muslim girls", born and raised in America, who, unlike her, had "experienced only personal freedom, a liberal edu­cation and economic opportunity". These girls could become "the standard-bearers of a new, more modern Islam" that would fuse Muslim traditions with "western openness".

The interesting question is what such a "modern" Islam might look like. But Hirsi Ali does not try to explore it. Instead, she expresses disappointment at the way that these girls seem to defend Islam from what they perceive as her "colonial feminism", instead of speaking out against "institutionalised Islamic misogyny". In doing so she accuses them of having a "black-and-white view of Islam" and lacking "a basic human empathy with other Muslim women" - criticisms that, ironically, are also often made of Hirsi Ali herself.

Nomad
Ayaan Hirsi Ali
Simon & Schuster, 304pp, £12.99

Hans Kundnani's "Utopia or Auschwitz" is published by C Hurst & Co (£16.99)