Quick Answer
Al-Ghazali attacks twenty philosophical doctrines by showing they fail the philosophers' own standard of proof, and along the way produces an analysis of causation that Hume would reach six hundred and fifty years later. He explicitly exempts mathematics and logic from the quarrel, which makes the popular claim that this book killed Islamic science difficult to sustain.
Key Takeaways
- The method is internal. He does not appeal to scripture against the philosophers. He argues that their conclusions do not follow from their premises by their own criteria.
- Three of twenty cross into unbelief: the eternity of the world, God's ignorance of particulars, and the denial of bodily resurrection. The other seventeen are a lesser charge.
- The fire and cotton argument is the landmark. Causal connection is not logically necessary, and we never observe the causing itself.
- He warns against attacking science on religious grounds, saying it damages religion by making faith look like ignorance.
- The Islamic decline story is not supported by historians of Islamic science, and the astronomy that followed him fed into Copernicus.
🕑 15 min read
What the Book Is
Abu Hamid al-Ghazali wrote Tahafut al-Falasifa, usually rendered as The Incoherence of the Philosophers, around 1095, when he held the most prestigious teaching chair in the Islamic world at the Nizamiyya in Baghdad.
The structure is twenty discussions, each taking one doctrine of the falasifa, the Muslim philosophers working in the Aristotelian and Neoplatonic tradition. Sixteen concern metaphysics and four concern the natural sciences. His principal target is Ibn Sina, known in the Latin West as Avicenna, whose synthesis was then the dominant intellectual system in Islamic lands.
Note the timing against his life. This is the work of the established public theologian, written before the crisis that ended his teaching career and sent him into eleven years of withdrawal and Sufi practice. The books from that later period, including The Alchemy of Happiness, sound like a different man, and in an important sense they are.
On the title: tahafut carries a sense of collapsing, falling apart, one thing bringing down the next. It is a structural image rather than a term of abuse. His claim is not that the philosophers are stupid but that their edifice does not stand up under its own weight.
The Book He Wrote First
Before attacking the philosophers, al-Ghazali summarised them, and the sequel is one of the better ironies in intellectual history.
Maqasid al-Falasifa, the Aims of the Philosophers, sets out Avicennan logic, metaphysics and physics accurately and without objection, so that his readers would understand the system before he took it apart. He says plainly that the refutation follows.
The book reached Latin Europe in the twelfth century, translated in Toledo, and it arrived without the sequel. Medieval European readers therefore encountered al-Ghazali as Algazel, an able expositor of Avicennan philosophy, and cited him as an authority within the school he had written the book to demolish. It took a long time for the misunderstanding to be corrected.
There is a lesson in it about how texts travel, and it belongs beside every other case in which a work arrives in a new culture with its frame removed.
The Method
The thing that makes this book philosophically serious rather than merely polemical is what al-Ghazali refuses to do.
He does not quote the Quran against the philosophers. He does not appeal to consensus or to authority. He accepts their standard, which is demonstrative proof in the Aristotelian sense, and argues that on that standard their metaphysical conclusions are not demonstrated at all. They have offered probable arguments and claimed necessity.
He is also careful about what follows from this. Showing that an argument fails is not showing that its conclusion is false. Through much of the book he is establishing that the philosophers cannot prove what they assert, which leaves the questions open rather than settling them in the other direction.
That is a modest and powerful position, and it is why the book has been read by people with no interest in defending Islamic orthodoxy.
The Three That Cross the Line
Al-Ghazali distinguishes carefully between error and unbelief, and the distinction had legal weight.
Seventeen of the twenty positions he classes as heretical innovation, which is a serious charge and not a capital one. Three he holds to be incompatible with Islam.
The eternity of the world. The philosophers held that the cosmos has always existed, proceeding necessarily from God as a consequence follows from a premise, with no first moment. Al-Ghazali argues this removes creation, makes God a cause rather than an agent, and leaves no room for will.
God's knowledge of particulars. On the Avicennan account God knows universals, the eternal structure of things, and does not know particular changing events, since knowing changing things would make the knower change. Al-Ghazali's objection is direct: a God who does not know what you did is not the God of any recognisable religion.
Bodily resurrection. The philosophers allowed survival of the rational soul and denied the resurrection of bodies. Al-Ghazali holds this to contradict explicit scriptural teaching in a way the other positions do not.
What is striking is how narrow he draws the line. Seventeen positions on which he thinks the leading philosophers of his civilisation are wrong, and he classes them as errors within the community. Three where he says the boundary has been crossed. A modern reader arriving expecting a blanket condemnation of philosophy finds a man doing careful triage, and the triage is itself a philosophical act.
Fire and Cotton
The seventeenth discussion is why this book is read in philosophy departments that have no interest in Islamic theology.
Al-Ghazali takes the plainest possible case. Fire touches cotton, the cotton burns. Everyone says the fire caused the burning. He asks what exactly is observed.
What is observed is the fire, then the burning. Observation gives you the sequence and the conjunction. It does not give you the causing, because there is no separate thing called causing available to be seen. And no contradiction arises from imagining the contact without the burning, which means the connection is not logically necessary in the way that a conclusion follows from premises.
His theological point is that God is the agent, acting directly or through angels, and that the regularity we observe is a habit of divine action rather than a necessity built into fire. But the analysis of what observation delivers stands independently of the theology.
David Hume made this argument in the eighteenth century and it became the foundation of modern philosophy of causation. Whether he knew al-Ghazali's version through the Latin tradition is disputed and probably unresolvable. What is not disputed is that the argument is here, in Arabic, around 1095.
Al-Ghazali is also alert to the obvious objection, that if causal connection is not necessary then nothing can be relied on and knowledge of nature is impossible. His answer is that God's habit is constant and can be known, so that the regularity science depends on is preserved while its metaphysical necessity is not. Scholars continue to argue about how far he personally held full occasionalism as against deploying it to show what his opponents could not prove.
What He Explicitly Exempts
Anyone repeating the claim that this book is an attack on science should read its introduction, because al-Ghazali addresses the point directly and with some force.
He states that logic and mathematics are not in dispute, that the philosophers' demonstrations in those fields are sound, and that no religious question turns on them. He goes further and warns religious people against attacking the philosophers on those grounds.
His argument for the warning is worth having in full. If a religious authority denounces a mathematical or astronomical result as impious, and an educated person knows that the result is demonstrably correct, that person will not conclude that the mathematics is wrong. They will conclude that religion depends on ignorance, and they will hold the authority responsible for teaching them so. Al-Ghazali says the harm done to religion by that manoeuvre is greater than any harm the philosophers do.
That passage, written around 1095, is a better statement of the problem than most that have been produced since. It does not say religion and science never conflict. It says that picking a fight you will lose on ground you do not understand costs you the credibility you need for the ground you do. Nine centuries later the same manoeuvre keeps being attempted with the same results, which suggests the argument is harder to hear than it is to state.
The Argument About the Eternity of the World
The first discussion is the longest in the book and it is where al-Ghazali is at his most inventive, so it is worth following one exchange in detail.
The philosophers argued that the world must be eternal. God is unchanging and perfect, so nothing new can arise in him. If the world began at a particular moment, God must at some point have moved from not creating to creating, which requires a change in him, and there could be no reason for that moment rather than any other, since one moment of empty time is indistinguishable from another.
Al-Ghazali's reply is to attack the assumption buried in the objection. The argument treats time as a container that was already running before the world began, so that God is imagined waiting inside it. But if time is itself created along with the world, the question of why God waited until that moment has no content, because there was no earlier interval in which the waiting could have happened.
He then presses the philosophers with a problem of their own. On their account the world proceeds from God by necessity, as a consequence follows from a premise. If so, God's will does nothing, and a God whose will accomplishes nothing is not the God either party claims to be defending.
Two things about this exchange are worth noticing. Augustine had reached a comparable position on created time some six hundred years earlier in a Christian context, which al-Ghazali is unlikely to have known. And the modern discussion of whether asking what came before the beginning is a well-formed question runs on the same track. The vocabulary has changed completely and the move has not.
Practice: separate cannot prove from is false
Al-Ghazali's whole method rests on a distinction most arguments collapse. Take a claim you disagree with and separate two questions: has the person given a valid proof, and is the claim true. They come apart constantly. A bad argument can have a true conclusion, and refuting the argument leaves the question open rather than settling it your way. Practising that separation for a week will make you a better reader of every controversy you meet, and it is the discipline that makes this book more than polemic.
Averroes Answers
About eighty years later, in Cordoba, Ibn Rushd wrote Tahafut al-Tahafut, the Incoherence of the Incoherence, and it is the other half of the conversation.
The form is unusual and useful: a running commentary that quotes al-Ghazali passage by passage and answers each in turn, so a reader gets both texts interleaved. Ibn Rushd defends the Aristotelian tradition across all twenty issues, and he argues that al-Ghazali has misunderstood the philosophers in places and misrepresented them in others.
His central counter-charge is about method. Al-Ghazali, he says, wrote different things for different audiences, giving the crowd one account and the learned another, and a man who does that has already conceded that the philosophers are right about the crowd.
On causality, Ibn Rushd's answer is that denying necessary connection in nature destroys the possibility of knowledge, since to know a thing is to know its causes. The exchange is one of the great disagreements in the history of philosophy and neither party won it outright.
Did It Kill Islamic Science
The claim circulates widely, including from popular science broadcasters, and it runs roughly as follows: al-Ghazali's attack on causation removed the rational foundation for natural science, Islamic civilisation turned away from inquiry, and a golden age ended.
Historians of Islamic science do not accept this, and the evidence against it is not subtle.
Astronomy after al-Ghazali was not in decline. The observatory at Maragha in the thirteenth century produced work of the first rank, including the mathematical device known as the Tusi couple. Ibn al-Shatir in fourteenth-century Damascus produced planetary models that resolve problems in Ptolemaic astronomy, and those models reappear in Copernicus in forms close enough that historians have argued at length about the transmission. Optics, medicine, mathematics and pharmacology all continued to produce significant work for centuries after 1095.
Ahmad Dallal's summary of the actual effect is the sharpest statement of the corrective: after al-Ghazali, the need to invoke religion to vindicate science decreased considerably. His reason for the decrease is the interesting part: science had stopped needing vindication. George Saliba's work on Islamic astronomy makes the same case from the technical side.
The decline that did eventually occur has causes historians debate, including the Mongol invasions, shifts in trade routes, and later political and economic changes. Attributing it to one book by one theologian is a story rather than a finding.
Which Edition to Read
Michael Marmura's edition in the Brigham Young University Islamic Translation Series is the standard. Parallel Arabic and English, introduction and annotation, and the translation is careful with the technical vocabulary, which matters enormously in a text like this. The second edition is the one to get.
Sabih Ahmad Kamali's translation from the 1950s is still circulating and is serviceable, and it lacks the apparatus.
Ibn Rushd's reply, in Simon van den Bergh's translation, is the necessary companion for anyone who wants the argument rather than one side of it.
On the cheap ebook editions: as with most out-of-copyright philosophical texts, inexpensive digital versions of this book are usually unattributed reprints of older translations, sometimes with the introductions and notes removed. In a work this technical the annotation is a large part of the value. Look for Marmura's name before buying.
Who Should Read It
Read it if you are interested in the philosophy of causation, in which case discussion seventeen is required and is about twenty pages.
Read it if you want to see what a first-rate mind does when it turns on the dominant system of its own civilisation from inside.
Read the introduction even if you read nothing else, for the passage on why attacking science on religious grounds harms religion.
Do not read it as an introduction to al-Ghazali the spiritual writer, who is a different figure and a later one. Do not read it without some Aristotle, since the arguments assume the framework.
Our position: a demanding, honest and unexpectedly modern book that has been blamed for the fate of a civilisation on evidence that does not support the charge. The causal argument alone puts it among the significant works of philosophy in any language, the triage between error and unbelief is more careful than its reputation, and the warning about picking fights with mathematics is one of the shrewdest things anyone has written on the subject. Buy Marmura, read discussion seventeen twice, and read Ibn Rushd afterwards.
For the surrounding tradition, see Sufi mysticism for the current al-Ghazali eventually joined, and Ibn Arabi for the metaphysics that developed in Islamic thought after this dispute.
Hume's argument, six hundred and fifty years early.
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Frequently Asked Questions
What is The Incoherence of the Philosophers?
Al-Ghazali's work of around 1095, in Arabic, attacking twenty doctrines held by the Islamic Aristotelian and Neoplatonic philosophers, principally Avicenna and al-Farabi. His method is to show that their conclusions do not follow from their own premises by their own standards of demonstration.
Who was al-Ghazali attacking?
Not philosophy in general and not the Greeks directly. His targets are the falasifa, the Muslim philosophers working in the Aristotelian and Neoplatonic tradition, above all Ibn Sina, known in Latin as Avicenna, whose synthesis was the dominant philosophical system in the Islamic world at the time.
What are the three doctrines he calls unbelief?
That the world is eternal rather than created in time, that God knows only universals and not particular things and events, and that there is no bodily resurrection. The other seventeen positions he attacks he classifies as heretical innovation rather than unbelief, which is a considerably lesser charge.
What is the argument about fire and cotton?
In the seventeenth discussion al-Ghazali argues that the connection between what we call a cause and what we call an effect is not logically necessary. We observe fire and burning together and never observe the causing itself. He anticipates Hume's analysis of causation by roughly six hundred and fifty years.
Was al-Ghazali against science and mathematics?
No, and he says so explicitly. He exempts logic and mathematics from the dispute and warns that attacking a philosopher's mathematics on religious grounds damages religion, because an educated person who knows the mathematics is correct will conclude that faith rests on ignorance.
Did this book kill Islamic science?
The claim is popular and historians of Islamic science reject it. Astronomy, mathematics, optics and medicine continued at a high level for centuries afterwards, including the Maragha observatory and the work of Ibn al-Shatir, whose planetary models reappear in Copernicus. Ahmad Dallal and George Saliba have documented this in detail.
What is the Maqasid al-Falasifa?
The Aims of the Philosophers, a neutral summary of Avicennan philosophy that al-Ghazali wrote first so that he could then refute it. When it reached Latin Europe separated from the refutation, medieval readers took al-Ghazali for a philosopher of the school he had set out to demolish.
Who replied to it?
Ibn Rushd, known in Latin as Averroes, wrote The Incoherence of the Incoherence about eighty years later. It is a running commentary that quotes al-Ghazali passage by passage and answers him, defending the Aristotelian tradition on all twenty issues, and it is the other half of the conversation.
Which translation should I read?
Michael Marmura's parallel Arabic and English edition, published in the Brigham Young University Islamic Translation Series, is the standard. It carries the Arabic facing the English, an introduction and annotation. Sabih Ahmad Kamali's earlier translation is also in circulation.
Is it difficult to read?
It is technical and demanding. Al-Ghazali writes as a trained philosopher arguing against philosophers, and following the arguments requires some familiarity with Aristotelian metaphysics and with Avicenna's positions. It rewards effort and it is not an introduction to anything.
Is al-Ghazali an occasionalist?
That is debated. He argues in the seventeenth discussion that causal connection is not necessary, which points toward occasionalism, and scholars disagree about how far he personally held the position as against deploying it to show that his opponents cannot demonstrate what they claim.
How does it relate to his other books?
The Incoherence is the work of the professional theologian at the height of his public career. The spiritual crisis that produced his Sufi turn came afterwards, and books like The Alchemy of Happiness and the Revival of the Religious Sciences belong to that later period and read completely differently.
Test the seventeenth discussion on your own kitchen
Boil a kettle and watch it. Then ask al-Ghazali's question honestly: what did you observe? You observed heat, then bubbles. You did not observe the causing, because there is nothing of that description available to be seen. Whatever you conclude about God, the observation is correct and it is the foundation of modern philosophy of science. It costs four minutes and it was first written down in Arabic more than nine hundred years ago.
Sources & References
- Al-Ghazali. The Incoherence of the Philosophers (Tahafut al-Falasifa), trans. M. E. Marmura, 2nd edition. Brigham Young University Press, Islamic Translation Series.
- Al-Ghazali. Maqasid al-Falasifa (The Aims of the Philosophers), translated into Latin in the twelfth century as the work of Algazel.
- Ibn Rushd (Averroes). Tahafut al-Tahafut (The Incoherence of the Incoherence), trans. S. van den Bergh. Gibb Memorial Trust.
- Dallal, A. Islam, Science, and the Challenge of History. Yale University Press.
- Saliba, G. (2007). Islamic Science and the Making of the European Renaissance. MIT Press.
- Stanford Encyclopedia of Philosophy. Entry on al-Ghazali. plato.stanford.edu.
- Internet Encyclopedia of Philosophy. Entry on al-Ghazali. iep.utm.edu.
- Hume, D. (1748). An Enquiry Concerning Human Understanding, for the later parallel argument on causation.