In 1585, Jacques du Perron presented to the court of the French king Henry III, as a kind of after-dinner entertainment, a formal logical argument for the existence of God. Du Perron, formerly a Protestant, was now well on his way to becoming a cardinal. He was a highly intelligent and rhetorically gifted man and he performed his task well, to the great pleasure of the assembled nobility. Flushed with success, he then turned to his audience and announced that, if they wanted, he could prove the opposite case too. The king was not amused.

Most of us like to believe that we believe what we believe because rigorous reasoning and reliable evidence have led us there. Most of us are wrong. It isn’t that reason and evidence play no role in our religion or lack of it; rather that they are saturated with deeper emotional, social and practical concerns. As Julian Barnes writes in The Sense of an Ending: ‘Most of us… make an instinctive decision, then build up an infrastructure of reasoning to justify it.’ Du Perron was no doubt very devout. Today he may well have been devoutly sceptical. But in neither case is he likely to have been led to his dis/belief through reason alone.

That the emotions matter is well established in the case of religious belief, as Stephen T. Asma’s fine recent study Why We Need Religion explains. But it is less well recognised when it comes to unbelief, and particularly the history of unbelief. Here we are still wedded to the romantic fable of fearless sceptics hacking their way through obscurantist bigotry, armed with nothing more than their trusty sword of reason.

In reality, as Alec Ryrie shows in this short but beautifully crafted history of early doubt, unbelief was (and is) chosen for ‘instinctive, inarticulate and intuitive’ reasons just as much as is belief. Ryrie is a Reformation scholar, but one with a particular interest and expertise in the culture of Protestantism. He adopts this approach in Unbelievers, arguing persuasively that unbelief was as much, if not more, about what people felt as what they thought, in particular a confluence of moral outrage and personal anxiety.

Beginning in the Middle Ages, termed an ‘age of suspicion’ rather than of faith, Ryrie describes medieval sceptics as being like contemporary flat-earthers. They had no evidence to support their position, but practised ‘a stubborn refusal to be hoodwinked by the intellectual consensus of their age’. Scepticism could dwell on the margins of society, particularly alehouses; among the professions, especially physicians; and even, if Machiavelli was later to be believed, among courtiers. But it was scepticism in the form of practical rather than theoretical atheism.

It wasn’t that philosophical ideas were altogether irrelevant, particularly once Lucretius’ bracingly naturalistic De Rerum Natura started doing the rounds. It was that such thinking tacked with the wind, rather than made it. Anticlericalism played a more important role than Epicureanism. As Ryrie writes: ‘Intellectuals and philosophers may think they make the weather but they are more often driven by it.’

Ryrie moves from the Middle Ages, through the swelling army of alleged atheists in the 16th century, to a particularly good chapter on the theatrical atheists of the Elizabethan and Jacobean stage. Always villainous, often incestuous, sometimes penitent, these monsters paraded the social and moral nightmare of godlessness before their audiences.

But this caricature left believers with a problem. For if the atheist ever abandoned his villainy, the faithful would lose the all-important moral high ground. Worse, if unbelievers started behaving in a more Christian way than Christians, they would capture an impregnable moral castle. Given that Christians spent much of the first half of the 17th century killing one another, this is pretty much what happened.

This is the heart of Ryrie’s argument: not that Christianity forged the intellectual weapons that its enemies thereafter used (though, in the development of textual criticism and the scientific method, it undoubtedly did that), but that it forged the moral ones. Early modern belief measured first the Church, then individual Christians, and then the Old Testament against the standards of Christianity — or more precisely, the standards of Jesus Christ — and found them all wanting. This was why so much early unbelief actually looked like further reformation and purification of faith, and why so many notorious infidels — Spinoza, Voltaire, Jefferson, Paine — singled out Jesus for praise. This wasn’t (simply) tactical. Jesus was the foundation of their infidelity.

Unbelievers covers much ground in a short space with deep erudition and considerable wit. The history of doubt is still in its relatively early stages. This is an important and convincing contribution to it.