Occasionalism and Divine Causality: The Critique of Necessary Natural Causes

Can we ever truly know that fire causes burning, or do we merely assume it from habit? What does that uncertainty reveal about the foundations of our reasoning? And if the greatest minds of two entirely different civilisations, separated by six centuries and a vast cultural ocean, arrived at the same unsettling doubt independently, what does that convergence tell us about the limits of human inference?

Abu Hamid al-Ghazali, the eleventh-century Persian theologian, jurist and mystic, is one of those thinkers who rewards patient reading in a way that few others do. His reputation in the medieval Islamic world was formidable, and his work The Incoherence of the Philosophers remains one of the most ambitious and rigorous exercises in philosophical critique that the pre-modern world produced. His target was the Aristotelian-inflected rationalism of thinkers such as Ibn Sina, who held that the natural world operates through necessary causal connections built into the very natures of things. Al-Ghazali found this claim philosophically presumptuous and theologically dangerous, and he set out to dismantle it with a precision that still commands respect.

The centrepiece of his critique is an example that has become famous in the history of philosophy: the relationship between fire and cotton. When fire is brought into contact with cotton, the cotton burns. This is something we observe repeatedly and reliably. But al-Ghazali asks a question that is deceptively simple. Do we actually observe fire causing the burning? Or do we observe only the two events occurring together, and then assume, on the basis of repeated experience, that the first produces the second? His answer is unambiguous. We observe conjunction. We observe sequence. We do not observe necessity. The necessity, he insists, is something the mind projects onto the world, not something it reads off from it.

This is a distinction of enormous philosophical importance. Al-Ghazali is pointing out that there is a gap between what the senses actually deliver and the conclusions our reason draws from that delivery. The cotton burns every time fire touches it, and so we come to regard the connection as necessary, as something that could not be otherwise. But that sense of necessity is a product of habit and expectation, not of direct observation. Nothing in the experience of fire and cotton actually shows us the mechanism by which one produces the other. We see what follows what; we do not see what compels what.

For al-Ghazali, embedded as he was in the Asharite tradition of Islamic theology, this insight had a specific theological upshot. If natural necessity cannot be demonstrated from observation, then the regularities of nature do not belong to nature itself. They belong to God. On the occasionalist account that al-Ghazali develops and defends, every event in the physical world is a direct act of divine will. Fire does not burn cotton because burning is built into the nature of fire. Fire is in the presence of cotton, and God wills the burning to occur. The conjunction is real. The necessity is divine. What looks like natural causation is, in truth, continuous divine activity, moment by moment sustaining and directing the world.

This position has sometimes been dismissed as a retreat into mysticism, but that reading is unfair and philosophically lazy. Al-Ghazali is not abandoning reason; he is disciplining it. He is insisting that reason must not claim more than experience can support. To assert that fire necessarily causes burning is to go beyond what observation warrants, and to import a metaphysical claim, namely that causal power is inherent in natural objects, that has not been earned through argument. His scepticism is rigorous, not merely pious.

The parallel with David Hume, writing in Scotland in the eighteenth century, is one of the most striking episodes of convergence in the history of ideas. Hume argued, with his characteristic lucidity and relentless consistency, that we never perceive causal power directly. We perceive one event followed by another, and after sufficient repetition, the mind develops a habit of expectation. We come to feel that the second event must follow the first, but that feeling of necessity is a feature of our psychology, not of the external world. Hume called this custom or habit, and he used it to show that our most confident causal beliefs rest on a foundation that is psychological rather than logical.

The resonance with al-Ghazali is not coincidental in the sense of being mysterious. Both thinkers were responding to a confident rationalism that overclaimed. Both noticed the same gap between observed sequence and inferred necessity. Both insisted that the mind does work that it then misattributes to the world. The difference lies in what each thinker placed on the other side of that gap. For Hume, the gap opened onto a kind of naturalistic humility: we are creatures of habit, and our causal reasoning is reliable enough for practical purposes, even if it cannot be philosophically grounded in necessity. For al-Ghazali, the gap opened onto God: the only genuine cause, the only true necessity, the sustainer of every regularity we confidently call natural.

What al-Ghazali teaches us, whatever our own theological commitments may be, is something of lasting value about the relationship between habit and knowledge. We are all, in our daily reasoning, inclined to treat regularities as necessities. We infer freely from past experience to future expectation, and we are right to do so, since the world is orderly enough that this serves us well. But the inference is not logically guaranteed. It rests on an assumption, namely that the future will resemble the past, that nature is uniform, that conjunctions we have observed will continue, and that assumption is itself not derived from observation but brought to it.

Perhaps that is the most important question al-Ghazali leaves us with. If our deepest confidence in the workings of nature rests on habit rather than demonstrated necessity, how carefully should we hold our most settled convictions? And what does it mean for the life of the mind to reason well, knowing that even our best tools carry this hidden limitation?