Fallibilism is one of the most important modern ideas. By fallibilism I mean the idea that no idea is in principle immune to revision. It is among the most important methodological principles for natural science. As Ann Druyan said, science “is forever whispering in our ears, ‘Remember, you’re very new at this. You might be mistaken. You’ve been wrong before.’” Many of the claims a Newtonian physicist would once have confidently made, have been shown to be false by Einsteinian and quantum physicists.

As it turns out, this crucial idea has important roots in Muslim thinkers who might reasonably be called fundamentalist.

Many identify William of Ockham as the founder of fallibilism. Natural-law theorists often bemoan Ockham’s influence, as Rod Dreher does in The Benedict Option. But the idea has much deeper and longer roots in the Muslim world. It goes back to conservative scripturalist Muslim jurists who stressed the Qur’an as the source of all reasoning about goodness in the world – and the fallibilism of human reason by comparison. This fallibilist idea goes back to relatively early Muslim fundamentalist thinkers like al-Ash’ari, but reaches its fullest flowering in the work of al-Ghazālī.

Abu Hamid Muhammad ibn Muhammad al-Ghazālī – al-Ghazālī, or just Ghazālī, for short – considered himself an opponent of philosophy, reasserting the authority of God’s scriptural revelation over the merely human activity of philosophy. Only that revelation, not anything merely natural, can tell us what is right and wrong. For God’s power is so great that he can do anything he wants; he is a will and not an intellect, and could make murder right and truthfulness wrong if that was his wish.

Such scripturalism must sound dogmatic to us. But it has an unexpected logical consequence, when applied – as Ghazālī does – beyond the ethical world to the physical world. If God can do absolutely anything he wants – contrary to the Aristotelian natural law theorists like ibn Sīnā, whom Ghazālī took as his philosophical foe – then there is no necessity in the natural world. For ibn Sīnā or ibn Rushd or Thomas Aquinas, we can deduce the nature of God from the nature of the world – and vice versa. At some level things have to be as they are; we know God wouldn’t have wanted it any other way.

But for Ghazālī that is not the case. There is no necessity in the world; to say that there was, would be to limit God’s power. So we must admit that there can be phenomena in the natural world that must surprise us. There are no laws in nature, only observed regularities and causal patterns. And those regularities and patterns are not necessary: “the connection between what is habitually believed to be a cause and what is habitually believed to be an effect is not necessary” (Incoherence of the Philosophers 170) Such a view – often known as occasionalism – is not so hard to square with the continued overturning of established certainties that characterizes modern natural science.

And indeed, I think it influenced our modern Western thinking about science. If Ghazālī’s thought here is sounding to you like David Hume’s, there is a reason. Hume was an avid reader of Nicolas Malebranche, a Cartesian rationalist known as the most famous occasionalist in Western tradition. Malebranche, having studied theology at Sorbonne, was well versed in the medieval scholastic debates that preceded him; those debates, including debates on occasionalism, owe a lot to Ghazālī. Whether Malebranche read Ghazālī’s work directly is not entirely clear, but he would have encountered Ghazālī’s ideas second- or third-hand in the many Christian works that came to respond to them. Especially: ibn Rushd quoted Ghazālī’s occasionalist arguments at length in order to refute them, and the widely read Thomas Aquinas incorporated those refutations of ibn Rushd (known to him as Averroës) at length into his own thought. While Aquinas’s anti-occasionalist position was official church doctrine, another Christian named Nicholas of Autrecourt had argued for occasionalism, to the point that he has been called the “fourteenth-century Hume” – and a 1969 article by Harry Wolfson argues that Autrecourt must have been familiar with Ghazālī’s arguments.

In short, Malebranche’s occasionalism very likely has its roots in Ghazālī at least indirectly, and Hume gets it from Malebranche. That great enemy of religious dogmatism turns out to owe one of his better ideas to a thinker who can rightly be called fundamentalist. And in turn, of course, Kant claims that Hume “woke him from his dogmatic slumber”; before reading Hume, Kant had thought that there was a necessary order to the phenomena of the material world. From then on, Kant recognized that any attempt at certain knowledge would have to be a priori, for empirical knowledge could always be refuted.

For that matter, William of Ockham himself had read ibn Rushd. When Ockham expresses skepticism about the necessity of causality, and his example – that the pattern of fire always burning combustible material does not mean fire is the cause of the burning – is one that appears directly in ibn Rushd’s quotations from Ghazālī. So Ockham’s fallibilism too seems to go back to Ghazālī – a thinker whose voluntarism Ockham shares.

Ockham, Hume, Kant – these thinkers together have played an enormous role in recognizing the fallibilism crucial to a natural-scientific project. The role of earlier Muslim thinkers in creating that fallibilism often goes unsung.