Quick Answer
Ibn Rushd was a judge, and the Decisive Treatise is a legal ruling: he asks whether Islamic law permits the study of philosophy and concludes that it requires it. It is ninety minutes of reading, it answers al-Ghazali at the root, and the double-truth doctrine attached to his name in Europe is the opposite of what he wrote.
Key Takeaways
- It is a fatwa, not a philosophical essay. He argues from scripture and legal analogy, ruling on a question of law from inside the law.
- The verdict is obligation. For those capable of demonstration, studying philosophy is not merely permitted but required.
- Three audiences, three kinds of argument. Demonstrative, dialectical and rhetorical, all addressed simultaneously by the same scripture.
- He never held the double truth. His own sentence: truth does not contradict truth but is consistent with it and testifies to it.
- The elitism is real, and an honest reader should sit with it rather than explain it away.
🕑 14 min read
What It Is
Abu al-Walid Muhammad ibn Rushd, known in Latin Europe as Averroes, wrote the Fasl al-Maqal around 1179. The full title translates roughly as the Book of the Decisive Treatise Determining the Connection Between the Law and Wisdom.
It is short. Modern editions run to a few dozen pages, usually printed with a companion piece called the Epistle Dedicatory and sometimes with a longer work on the methods of proof.
Ibn Rushd was born in Cordoba in 1126 into a family of jurists. His grandfather and father had both served as chief judge of the city. He held judicial appointments in Seville and Cordoba, served as physician to the Almohad caliph, and produced the commentaries on Aristotle that made his name in three civilisations.
On the timing: this arrives roughly eighty years after al-Ghazali's Incoherence of the Philosophers, and Ibn Rushd had read it closely. He wrote a full point-by-point reply, the Incoherence of the Incoherence. The Decisive Treatise is the shorter and prior argument: before defending any philosophical conclusion, establish that the inquiry is lawful.
A Ruling, Not an Argument
The single most important thing to understand about this text is its genre, and most summaries skip it.
Ibn Rushd does not open by defending philosophy. He opens by posing a question in the standard form of Islamic jurisprudence: what is the status, under the Law, of the study of philosophy and logic? Is it permitted, prohibited, recommended, or required?
Those are the legal categories a Muslim jurist works with, and the question as posed can only be answered by legal methods. So Ibn Rushd proceeds as a judge. He cites scriptural texts as evidence, applies analogical reasoning of the kind used to derive rulings on new cases, and reaches a verdict.
This is a substantially stronger position than philosophy defending itself. A philosopher arguing that religion should permit philosophy has already conceded that religion is the authority and philosophy the petitioner. Ibn Rushd instead speaks as the authority, in its own language, and delivers a ruling that binds.
The Case From Scripture
The evidence he assembles is Quranic, and the move is elegant.
The Quran repeatedly commands reflection on the created world. It tells its hearers to consider, to look, to take heed, to reflect on the heavens and the earth and what is in them. Ibn Rushd takes these commands seriously as commands.
If reflection on created things is commanded, then reflection carried out properly is commanded. Reflection carried out properly means reasoning validly from what is observed to what follows, and the discipline that studies valid reasoning is logic. The tools of demonstration are therefore required equipment for obeying an explicit instruction.
He adds a further step that answers the obvious objection. The Greeks developed these tools. Does using them import something foreign into Islam? His answer is that a tool is judged by whether it works, in the way a Muslim may use a knife made by a non-Muslim to perform a lawful slaughter. What matters is whether the instrument is sound.
The conclusion is stronger than toleration. For a person with the capacity for demonstrative reasoning, the study of philosophy becomes obligatory, and neglecting it is a failure to obey a command. Ibn Rushd has taken the charge that philosophy is a foreign intrusion and converted it into a religious duty, using only materials his opponents accept.
Three Audiences
The framework doing most of the work in the treatise is a division of people by what actually persuades them.
The demonstrative. A small group capable of following strict proof from certain premises to necessary conclusions. They assent because a thing has been shown.
The dialectical. Those who reason from probable or widely accepted premises rather than certain ones. Ibn Rushd places the theologians here, and it is not a compliment.
The rhetorical. The great majority, persuaded by vivid images, examples and eloquence rather than by argument at all.
His claim about scripture follows: the Quran is remarkable precisely because it addresses all three at once. The same passage offers an image to one reader, a probable argument to another, and material for demonstration to a third. A text that could reach only philosophers would have failed as revelation to a whole community.
The pastoral rule he derives is that each class should be taught in its own mode. Give a rhetorical hearer a demonstration and you will not persuade them; give them an allegorical reading of a passage they hold literally and you may destroy their faith without putting anything in its place.
Allegory and Its Limits
The hardest question in the treatise is what happens when a demonstrated conclusion appears to contradict the plain sense of scripture.
Ibn Rushd's answer rests on a principle he states directly, and it is the sentence to carry away from the book: truth does not contradict truth but is consistent with it and testifies to it.
Both revelation and demonstration come from the same source. Two things that are both true cannot really conflict. So an apparent conflict is a signal that something has been misread, and since a valid demonstration cannot be set aside, the reading of the text must be adjusted. The passage is to be interpreted allegorically, by ta'wil.
He puts real limits on this. Only those trained in demonstration may perform it. Some passages are not subject to it at all. And the interpretation, once reached, is not to be published to those who cannot follow the reasoning behind it.
The Uncomfortable Part
That last restriction deserves a paragraph of its own rather than a defence.
Ibn Rushd holds that certain understandings should be withheld from most people. His reason is never that the understandings are false. It is that the recipients lack the equipment to hold them, and that handing them over does damage. He is explicit that publishing allegorical interpretations to the general public is harmful and that those who do it are responsible for the harm.
Modern readers should not smooth this over. It is a claim that a religious community is properly stratified by intellectual capacity, and that the truth a person receives should be calibrated to what they can bear. It sits badly with any commitment to open inquiry or to equal access to knowledge.
Two things can be said in fairness, and neither dissolves the objection. The first is that Ibn Rushd's motive is pastoral rather than contemptuous. He has watched theologians publicise disputes that unsettled ordinary believers without giving them anything better, and his concern is for those people. The second is that his position was not eccentric. Al-Ghazali held a version of it, and so did a great deal of the philosophical tradition in three religions. What has changed is not that the argument was refuted. It is that a different value, the presumption that adults are entitled to whatever is true, eventually displaced it.
The Commentaries That Made His Name
The Decisive Treatise is the argument about whether the work may be done. The work itself was enormous, and knowing its shape explains why Europe cared so much.
Ibn Rushd commented on nearly the whole Aristotelian corpus, and he did it at three levels of depth. There are short epitomes that summarise a work's doctrine. There are middle commentaries that paraphrase and clarify, aimed at an educated reader who needs the argument made plain. And there are long commentaries that quote Aristotle passage by passage and then expound each section at length, which is where his own positions emerge most fully.
The project had a specific motive. Ibn Rushd believed Aristotle had been distorted by the Neoplatonic material that had accumulated around him in Arabic, above all through Ibn Sina, and that the task was to recover what Aristotle had actually said. He is a restorer by intention, working against several centuries of accretion.
That aim is what made him indispensable in Latin Europe. Thirteenth century masters receiving Aristotle in translation needed someone to tell them what the text meant, and Ibn Rushd had produced exactly that, at three levels of difficulty, across the whole corpus.
The irony sits at the centre of his reputation. A man remembered in Europe chiefly as a commentator on someone else was, in his own community, a chief judge, a court physician, an author of medical encyclopaedias, and an independent philosopher who wrote the book under review here entirely in his own voice.
Practice: find your three audiences
Ibn Rushd's division travels well beyond religion. Take something you understand well and try explaining it three ways: as a rigorous argument for someone who wants the proof, as a plausible case for someone who wants a reason to accept it, and as an image for someone who needs to feel why it matters. Most people can do one of the three and assume the other two are dishonest. His claim is that all three are legitimate and that using the wrong one is the actual failure.
The Doctrine He Never Held
In thirteenth century Paris, a body of teaching called Latin Averroism developed among masters of the arts faculty, associated above all with Siger of Brabant, and it acquired a reputation for holding that something can be true in philosophy and false in theology.
That position, the double truth, was condemned at Paris in 1277 in a sweeping list of propositions, and the name attached to it was Averroes.
He did not hold it, and this treatise is where you can check. His entire method depends on truth being single. The whole apparatus of allegorical interpretation exists precisely because he refuses to let two contradictory things both stand. If revelation and demonstration seem to conflict, one of them has been misread, and the work is to find out which.
Whether Siger himself held the double truth is disputed by medievalists, and some think the doctrine was largely constructed by opponents as a charge to condemn. Either way, the attribution to Ibn Rushd is a misreading that travelled for centuries and still appears in summaries of his thought.
Answering al-Ghazali
The two books belong together and are best read in sequence.
Al-Ghazali argued that the philosophers had failed to demonstrate their metaphysical conclusions by their own standard, and that three of their positions crossed into unbelief. Ibn Rushd's long reply contests the arguments one by one.
The Decisive Treatise operates at a different level and is the more fundamental of his two responses. Al-Ghazali's book had the practical effect of making philosophy suspect. Ibn Rushd's reply at this level is that the suspicion itself is unlawful: the Law requires the inquiry, so shutting it down is not piety but disobedience.
He also turns al-Ghazali's own conduct against him. Al-Ghazali wrote at different levels for different audiences, addressing scholars in one register and the general reader in another. Ibn Rushd's point is that a man who does that has already accepted the three-audience theory, and cannot then object to philosophers doing the same.
The Argument About Borrowed Tools
One move in the treatise deserves separating out, because it settles a question that recurs in every tradition that meets another one.
The objection Ibn Rushd is answering runs like this. Logic and demonstration were developed by Greeks, who were pagans. Importing their methods imports something alien into the community, and the alien thing will corrupt what it touches.
His reply is that an instrument is assessed by whether it works. If a previous people worked out how valid inference operates, a Muslim examining their results should check whether the reasoning is sound, and if it is sound, use it. Refusing a correct method because of who discovered it is not caution. It is discarding something true.
He extends this with an argument about cumulative labour. No individual and no generation can rebuild a whole science alone. Geometry took centuries. If each community had to derive everything from nothing rather than inheriting what earlier ones established, no science would ever mature. Building on predecessors is how knowledge works, and the predecessors' religion has nothing to do with the validity of their proofs.
The argument holds up entirely and it has been made badly in a hundred contexts since. A community encountering an outside body of knowledge asks whether accepting it means accepting the worldview that produced it. Ibn Rushd's separation of the tool from the toolmaker is one of the cleanest answers anyone has given, and he gave it in the twelfth century in a legal ruling.
What Happened to Him
The ending is not a happy one, and it explains a great deal about the later history of both traditions.
Around 1195, in a political shift under the Almohad regime, Ibn Rushd fell from favour. He was banished, his teaching was condemned, and some accounts report that his books were burned. He was restored shortly before his death in 1198.
His philosophical influence in the Islamic world largely ended there. The tradition that continued was the one al-Ghazali stood in, and the Aristotelian project Ibn Rushd represented did not find major successors in Arabic.
In Latin Christendom and in Jewish philosophy it was the opposite. His commentaries on Aristotle were translated into Latin and Hebrew and became the standard apparatus for reading Aristotle in the medieval universities. Thomas Aquinas calls Aristotle the Philosopher and calls Ibn Rushd simply the Commentator, arguing against him constantly and relying on him throughout. Jewish thought absorbed him just as deeply through the Hebrew versions.
A Muslim judge from Cordoba, banished at home, became one of the shaping intelligences of Christian and Jewish philosophy for three hundred years.
Who Should Read It
Read it if you have read al-Ghazali and want the other side. Ninety minutes, and the two together are one of the great arguments in the history of thought.
Read it if you are interested in how a religious tradition can make room for inquiry from inside its own commitments rather than by weakening them.
Read Butterworth's edition, which gives the Arabic facing the English in the same series that produced the standard al-Ghazali. Having both on a shelf in matching volumes is a small pleasure and a genuine convenience.
Do not read it expecting the Aristotelian philosophy. This is the argument about whether that work may be done, and the work itself is in the commentaries.
Our position: a short, formally brilliant document that does something rarer than either defending or attacking religion. It rules, in the voice of the tradition, that the tradition requires the inquiry it is suspected of forbidding. The single sentence about truth not contradicting truth is worth the book, the three-audience theory explains more than it should for something so simple, and the restriction on who may be told sits uneasily and should be left sitting uneasily.
For the surrounding material, see The Alchemy of Happiness for al-Ghazali's other side, and Ibn Arabi for the direction Islamic metaphysics actually took after this dispute.
Ninety minutes, and the other half of the argument.
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Frequently Asked Questions
What is The Decisive Treatise?
A short work by Ibn Rushd, known in Latin as Averroes, written around 1179, asking whether Islamic law permits, forbids or requires the study of philosophy. He answers as a judge issuing a ruling rather than as a philosopher making a case, and concludes that philosophy is obligatory for those capable of it.
Why does the form matter?
Because it is a legal opinion, not a philosophical treatise. Ibn Rushd was a working judge, and he argues using the tools of Islamic jurisprudence: scriptural proof texts and analogical reasoning. He is not asking philosophy to justify itself to religion; he is ruling on a question of law from inside the law.
What are the three classes of people?
Ibn Rushd divides people by the kind of argument that persuades them: the demonstrative, who follow strict proof, the dialectical, who reason from probable premises, and the rhetorical, who are moved by images and persuasion. Scripture addresses all three at once, and each should be taught in its own mode.
What is ta'wil?
Allegorical interpretation. Ibn Rushd holds that where demonstrative proof conflicts with the apparent sense of a scriptural passage, the passage should be read allegorically, because both come from the same source and cannot really conflict. He restricts the practice to those trained to do it.
Did Averroes teach a double truth?
No. The doctrine that religion and philosophy can hold contradictory truths was attributed to his Latin followers and condemned at Paris in 1277. His own position is the opposite, stated plainly in this text: truth does not contradict truth but is consistent with it and testifies to it.
How does it relate to al-Ghazali?
Ibn Rushd wrote a full point-by-point reply to al-Ghazali's Incoherence of the Philosophers, called The Incoherence of the Incoherence. The Decisive Treatise is the shorter and more fundamental argument underneath it, establishing that the inquiry is lawful before defending any particular conclusion.
Is the argument elitist?
Yes, by any modern standard. He holds that allegorical readings should be withheld from people unequipped to receive them, and that teaching the wrong method to the wrong audience damages their faith. He offers a pastoral justification and it remains a claim that some truths are not for everyone.
What happened to Ibn Rushd?
He served as judge in Seville and Cordoba and as physician to the Almohad court, then fell from favour late in life, was banished around 1195, and some accounts say his books were burned. He was restored shortly before his death in 1198, and his philosophical influence in the Islamic world largely ended with him.
Why was he so important in Europe?
His commentaries on Aristotle were translated into Latin and Hebrew and became the standard aids to reading Aristotle in the medieval universities. Aquinas calls Aristotle the Philosopher and Ibn Rushd simply the Commentator. Jewish philosophy absorbed him equally deeply through the Hebrew versions.
Which translation should I read?
Charles Butterworth's parallel Arabic and English edition, published by Brigham Young University Press in 2001, is the standard. George Hourani's earlier translation, issued as On the Harmony of Religion and Philosophy, is also widely used and remains valuable.
How long is it?
Very short. The treatise itself can be read in an hour and a half, and modern editions usually print it with the Epistle Dedicatory and sometimes with the Exposition of the Methods of Proof, which together make a fuller picture of his position.
Is it still relevant?
The specific question of whether a religious community may study philosophy recurs in every tradition. So does the harder question underneath it: what a community does when a demonstrated result appears to contradict a sacred text. Ibn Rushd's answer is one of the few that respects both sides of the problem.
Apply the principle to your own contradiction
Find something you hold on authority and something you hold because you have checked it, where the two appear to disagree. Then apply Ibn Rushd's rule: two true things cannot really conflict, so one of them has been misread. Work out which, honestly, without deciding in advance. Most people discover the conflict was between a demonstrated result and a hasty reading of the authority rather than the authority itself, which is exactly what he predicted eight hundred years ago.
Sources & References
- Averroes (Ibn Rushd). Decisive Treatise and Epistle Dedicatory, trans. C. E. Butterworth. Brigham Young University Press, 2001.
- Hourani, G. F., trans. Averroes: On the Harmony of Religion and Philosophy. Gibb Memorial Trust.
- Averroes. Tahafut al-Tahafut (The Incoherence of the Incoherence), trans. S. van den Bergh.
- Al-Ghazali. The Incoherence of the Philosophers, trans. M. E. Marmura. Brigham Young University Press.
- Condemnation of 1277, University of Paris. The list of propositions associated with Latin Averroism.
- Stanford Encyclopedia of Philosophy. Entry on Ibn Rushd. plato.stanford.edu.
- Aquinas, T. Summa Theologiae and the Aristotle commentaries, for his use of Ibn Rushd as the Commentator.
- University of Chicago Press. Publication record for the Butterworth edition.