Towards the end of this illuminating book, Larry Siedentop describes a fourteenth century battle between two Christian monastic orders. The Dominicans and the Franciscans were mendicant orders, begging monks who had abandoned the comforts of the cloisters to preach among the poor.

Dominicans emphasised the role of rationality and 'correct' doctrine; Franciscans highlighted the importance of moral equality and human agency, emphasizing the 'spirit' rather that the 'letter' of faith. Dominicans were deeply influenced by Thomas Aquinas, perhaps the greatest of theologians, and the driving force in the reintroduction of Aristotelian ideas into Christian thought. Franciscans worried that such borrowing from Aristotle's theory had corrupted Christian belief.

One way to think about Inventing the Individual is as an attempt to restore the Franciscan spirit to both intellectual history and the Christian tradition. Siedentop rewrites the story of Western liberalism not merely to establish it as a Christian project, but also to infuse it with the Franciscan view of faith, politics and human nature.

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The conventional view of liberalism is as a product of modernity, a philosophy that developed through the Renaissance and the Enlightenment primarily in opposition to religion. On the contrary, Siedentop insists, liberalism is "a child of Christianity". The liberal concept of the individual was invented by theologians. And secularism is "Christianity's greatest gift to the world".

The critical historical cleavage for Siedentop lies not between modernity and premodernity, but between the Ancient world and Christianity. Thanks largely to the Renaissance, we tend to see the Ancient world as the source of modern humanism. In fact, Siedentop observes, Ancient Greece was a deeply religious society built upon an unshakeable belief in natural inequality. The Greeks possessed no concept of the individual, separate from the family or the city, nor a notion of free will.

Christianity revolutionised this worldview. At its heart were two claims: those of moral equality and human agency. God had created humans as equals, and as rational agents with free will. These two ideas, Siedentop suggests, were first formulated by St Paul, possibly the "greatest revolutionary in human history". Siedentop traces the development of these concepts through the Christian tradition, from Augustine, who with Aquinas stands as the most influential of its theologians, through to the medieval philosophers who helped fashion canon law, asserting that "'experience' is essentially the experience of individuals", and that "a range of fundamental rights ought to protect individual agency", so establishing the foundations of liberalism. Only the "anti-clericalism" of subsequent centuries has, Siedentop insists, obscured the roots of liberalism in Christianity.

Inventing the Individual is beautifully written and rigorously argued. Siedentop usefully challenges the conventional narrative about the development of the Western intellectual tradition. But the story he tells in reframing that narrative is itself deeply problematic. Consider the issue around which Siedentop builds his whole account: the tension between the Ancient belief in natural inequality and the Christian idea of moral equality. Christianity certainly played a major role in developing notions of equality and universal visions of humanity. Yet, ideas of hierarchy and inequality remained central to the Christian tradition. "It is in the natural order of things", Augustine preached, "that women should serve men, and children their parents, because this is just in itself, that the weaker reason should serve the stronger." It was given by nature for the lower orders to serve the upper orders.

Siedentop regards such claims as remnants of an ancient way of thinking. Yet, so central have such ideas been to Christian thought that it seriously distorts the history of that tradition to dismiss them as lightly as Siedentop does.

Siedentop disregards, too, the distinctiveness of modern notions of equality. Christian equality was tied to religious belief; hence the long and fractious debates about whether non-Christians were equal, or even possessed souls. The crumbling of belief in a God-ordained order helped, in the sixteenth and seventeeth centuries, to develop a new, radical, inclusive form of egalitarianism. Having dispensed with God, there was, as the historian Jonathan Israel has put it, no "meaningful alternative" to grounding morality in a "generalised radical egalitarianism extending across all frontiers, class barriers and horizons." The new egalitarians drew upon radical strands of Christian thought. But they transformed the very meaning of equality.

Like the best books, Inventing the Individual both teaches you something new and makes you want to argue with it. Its real strengths lie, however, more in raising questions than in providing answers.