There are different classes of men who fall roughly into three groups. The highest of these are those whose religious belief is based on demonstration (burhan), the result of reasoning from syllogisms which are à priori certain; these are the men to whom the philosopher makes his appeal. The lowest stratum contains those whose faith is based on the authority of a teacher or on presumptions which cannot be argued out and are not due to the exercise of pure reason; it is mischievous to put “demonstration” or reason or controversy before people of this type, for it can only cause them doubt and difficulty. Intermediate between these two strata are those who have not attained the use of pure reason—which, with Ibn Rushd, seems to be simply intuition—but are capable of argument and controversy by means of which their faith can be defended and proved; “demonstration” proper is not to be laid before these, but it is right to enter into argument with them and to assist them to rise above the level of those whose belief is based only upon authority.
Most of all, Ibn Rushd opposed the teaching of the mutakallimin or orthodox scholastic theologians, whom he regarded as subverting the pure principles of the Aristotelian philosophy, and of these he considered the worst to be al-Ghazali, “that renegade of philosophy.” His leading controversial work is the Destruction of the Destruction (Tahafat at-Tahafat), which he designed as a refutation of al-Ghazali’s Destruction of the Philosophers.
But it was as a commentator on the text of Aristotle that he became best known to subsequent generations amongst the Jews and the later Latin scholastics; he was the great and final commentator. Strangely, however, Ibn Rushd never perceived the importance of reading Aristotle in the original; he had no knowledge of Greek, and gives no sign of supposing that a study of the Greek text would at all assist a student of the philosopher. The method of his commentaries is the time-honoured form derived from the Syriac commentators: a sentence of the text is given and the explanatory comments follow.
In main substance Ibn Rushd reproduces the psychology of Aristotle as interpreted by al-Farabi and Ibn Sina, but with some important modifications. In man is a passive and an active intellect: the active intellect is roused to action by the operation of the Agent Intellect, and thus becomes an acquired intellect; the individual intellects are many, but the Agent Intellect is but one, though present in each, just as the sun is one, but there are in action as many suns as there are bodies which it illuminates. This is the form of the Aristotelian doctrine as it had been transmitted through Ibn Sina; the Agent Intellect is one, but it is as by emanation present in each, so that the quickening power in each one is part of the universal Agent Intellect. But Ibn Rushd differs from his predecessors in his treatment of the passive intellect, the `aql hayyulani, which is the seat of latent and potential faculties upon which the Agent operates. In all the earlier systems this passive intellect was regarded as purely individual and as operated on by the emanation of the universal Agent, but Ibn Rushd regarded the passive intellect also as but a portion of a universal soul and as individual only in so far as temporarily occupying an individual body. Even the passive powers are part of a universal force animating the whole of nature. This is the doctrine of pampsychism, which exercised so strong an attraction for many of the mediæval scholastics, and has its adherents at the present day; thus James (Principles of Psychology, p. 346) says: “I confess that the moment I become metaphysical and try to define the more, I find the notion of some sort of an anima mundi thinking in all of us to be a more promising hypothesis, in spite of all its difficulties, than that of a lot of absolutely individual souls.” Ibn Rushd regards Alexander of Aphrodisias as mistaken in supposing that the passive intellect is a mere disposition; it is in us, but belongs to something outside; it is not engendered, it is incorruptible, and so in a sense resembles the Agent Intellect. This doctrine is the very opposite to what is commonly described as materialism, which represents the mind as merely a form of energy produced by the activity of the neural functions. The activity of brain and nerves, according to Ibn Rushd, are due to the presence of an external force; not only, as Aristotle teaches, at least according to Alexander Aph.’s interpretation, is the highest faculty of the reason due to the operation of the external one Agent Intellect, but the passive intellect on which this agent acts is itself part of a great universal soul, which is the one source of all life and the reservoir to which the soul returns when the transitory experience of what we call life is finished.
Ibn Rushd’s views do not receive much attention or criticism from Muslim scholars, but the Christian scholastics brought two main arguments against this theory, one psychological, the other theological. The psychological objection is that it is entirely subversive of individuality: if the conscious life of each is only part of the conscious life of a universal soul there can be no real ego in any one of us; but there is no fact to which consciousness bears clearer witness than the reality and individuality of the ego. This did not touch the possibility that the individual soul might be drawn from a universal soul as its source, nor did it disprove that the individual soul might be reabsorbed again in the universal soul, but in so far as Ibn Rushd’s view represented the soul as throughout a part of the universal soul it was argued that this is contrary to experience, which makes it clear that in this present life the ego is very distinctly individual. The theological argument was that Ibn Rushd’s view denied the immortality of the soul, and so was contrary to the Christian faith. This objection deals more specifically with the reabsorption of the soul of the individual in the universal soul; such cessation of separate and individual existence, it was argued, meant that the soul as such no longer existed.
As we have already noted, Aristotle gives a rather narrow range to the highest faculty of reason, confining its activity to the perception of abstract ideas; “as to the things spoken of as abstract (the mind) thinks of them as it would of the being snub-nosed, if by an effort of thought it thinks of it qua snub-nosed, not separately, but qua hollow, without the flesh in which the hollowness is adherent: so when it thinks of mathematical forms, it thinks of them as separated, though they are not separated” (Aristot. de anima. iii. 7, 7-8). Those who followed Alexander Aph. and the neo-Platonists took this “abstract” in a very narrow sense, and in the Arabic commentators these abstractions even become non-substantial beings, as it were disembodied, or rather bodiless, spirits: “in quibusdam libris de Arabico translatis substantiae separatae, quae nos angelos dicimus, intelligentiae vocantur” (S. Thos. Aquin. Quaest. Disp. de anima. 16). Can man know these substantiae separatae by his natural faculties? Ibn Rushd says he can: if otherwise nature has acted in vain, for there would be an intelligibile without an intelligens to understand it; but Aristotle has shewn (Polit. 1, 8, 12) that nature does nothing in vain, so that if there be an intelligibile there must be an intelligens capable of perceiving it. “The commentator (i.e. Ibn Rushd) says in 2 Met. comm. i. (in fine) that if abstract substances cannot be understood by us then nature has acted in vain, because it made that which is by nature understandable in itself to be not understood by anyone. But nothing is superfluous or in vain in nature. Therefore immaterial substances can be understood by us.” (S. Thos. Aquin. Summa. 1, 88.)
As the Agent Intellect enters into communication with relative being it has to suffer the conditions of relativity, and so is not equally efficient in all; it acts on sensible images as form acts on matter, yet the Agent Intellect never becomes corruptible as that on which it acts.
These are in outline the points in the teaching of Ibn Rushd, which show the most marked differences from that of his predecessors, and which afterwards provoked most controversy amongst the Latin scholastics.
Ibn Rushd really ends the illustrious line of Arabic Aristotelians. A few Aristotelian scholars followed in Spain, but with the decay of the Muwahhid power these came to an end. Of those later scholars we may mention Muhyi ad-Din b. `Arabi (d. 638) and `Abdu l-Haqq b. Sab`in (d. 667). The former of these was primarily a Sufi, and shows a strong inclination towards pantheism. `Abdu l-Haqq, the last of the Muwahhid circle, was also a Sufi, but at the same time an accurate student of Aristotle. In modern Islam there is no Aristotelian scholarship, save only in logic, where Aristotle has always held his own.