Averroes defended philosophy by returning to the true Aristotle. For this purpose, Aristotle's book “On the Heaven,” in which he explained the eternity, uniqueness and movement of the universe, occupied a place of special importance. But the Aristotelian philosopher had a hard time holding his own in the face of contradictions within the book and with respect to Aristotle's later works. In his early Compendium, later Paraphrase, and final Long Commentary of De Caelo, Ibn Rushd continued the efforts of the Hellenistic commentators in order to integrate all the elements of his doctrine into a unified system, to harmonize his early cosmology with his later Metaphysics – the early doctrine of natural movement of the elements, and of the self-moving star-souls (a Platonic element), with the doctrine of potency and actuality and the theory of the First Mover – and to uphold his models of homocentric planetary spheres against the mathematical paradigm of Ptolemaic astronomy. By insisting throughout on demonstrative arguments based on rational principles, he asserted the philosophers' claim to irrefutable truth.

Ibn Rušd devoted a certain number of works to Aristotle's Prior Analytics. In a series of opuscules written over a period of twenty years and following upon his Middle Commentary on Aristotle's Prior Analytics, he faced a problem particular to the modal syllogism – that of the mood of the conclusion in mixed syllogisms.

The problem can be stated as follows: At the beginning of the Prior Analytics, Aristotle established a formal deductive principle – that of universal attribution (Pr. An. I.1.24b26–30). Applied to the modal syllogism, this principle is inadequate as stated. It is too general to be applied in a univocal manner in all modal syllogisms. To preserve a sense of coherence in Aristotle's declarations, the commentators had to interpret it. Presenting the interpretations of the commentators, primarily al-Fārābī and Alexander, on the basis of al-Fārābī's Large Commentary on Aristotle's Prior Analytics, Averroes criticizes them. Applied according to Alexander's interpretation, the principle of universal attribution is valid only for modal syllogisms one of whose premises is necessary and the other assertoric; according to al-Fārābī's interpretation, it is verified only when the minor premise is possible. Averroes proposes two preliminary solutions. Either this formal deductive principle must be applied differently according to the modal differences of the minor premises in mixed syllogisms (first solution) or would be used in two ways, generally or in keeping with each mood (second solution). These solutions are not satisfactory, for they call into question the unity and universality of the principle of universal attribution as established by Aristotle. What is the utility, Averroes asks, of a principle which does not hold for all modalities or does not apply to all the premises when the Pr. An. ought to furnish formal and universal principles of deduction? And why did Aristotle define the principle of universal attribution without distinguishing its application according to each of the three modal premises? Returning at the end of his career to a literal exegesis of Aristotle's propositions and without harkening back to the earlier solutions, he proposes a theory of making the terms modal (fourth solution) in order to save Aristotle's declarations with respect to the principle of universal attribution and the mood of the conclusion of mixed syllogisms (Pr. An. I. 9.30al5–20). Though formally inadequate, this solution, which had a continued history, proposes a new way of looking at the classification of modal propositions.

This article claims that Averroes wrote his Middle Commentary on the De anima after he composed both his Short and Long commentaries. A close comparison of the two texts proves that he had the Long commentary before him when composing the Middle. This has implications both for the development of Averroes' doctrine of the intellect, and for understanding Averroes' style of composing commentaries.

What follows is a detailed study of Averroes's Decisive Treatise based on a new English translation of the text. It seeks to reveal the steps of the exposition, the quality of the reasoning used therein, and the general goal. The study adheres closely to the framework established by Averroes at the outset: namely, that this is an inquiry conducted from the perspective of what is permitted by the divine law of Islam. And it takes seriously the proposition that one can seek for an intelligent and intelligible connection between that law and the results reached through philosophical investigation. Thus, Averroes's ultimate conclusion – that the divine law of Islam and philosophy or wisdom are in basic agreement – is seen to make sense insofar as both seek to provide for the well-being of all members of the community. It makes sense, that is, as an understanding of what governance entails.