(Translations from Greek)

As most of you are aware, the Islamic state, which the prophet Muhammad had founded in Madinah in the 7th century A.D., expanded very rapidly in the following years, so that by the middle of the 8th century we find Muslims in control of the lands stretching all the way from Spain in the West to the borders of India in the East.

Now the people living in those conquered areas were for the most part Christians who, particularly in Syria and Iraq, had for some time been students of Greek philosophy and science and had translated many Greek works into Syriac, which was the language they were using at the time of the Muslim conquests. Later during the ninth century, at the command of the Muslim caliphs, they translated these Greek works from Syriac into Arabic and often directly from Greek into Arabic. Among the Greek works which they translated during this period were all the works of Aristotle with the exception of his Politics, Plato's Timaeus, Republic, and Laws, and various works of such neo-Platonists as Proclus, Porphyry, Plotinus, and others. It is through these translations from Greek into Arabic that Muslims became acquainted with Greek philosophical thought.

(The Muslim philosophers)

What we call Islamic or Arabic philosophy is then a continuation and revival of the late Greek philosophical tradition undertaken by people who were nominally Muslims and who used Arabic instead instead of Greek and Syriac. Let me mention a few of the most famous of these Muslim philosophers:

al-Kindi, of Arab descent, died sometime after 870 A.D.

al-Razi, perhaps the most free-thinking of Muslim philosophers, died about 923 A.D.

al-Farabi, of Turkish descent, was known among Muslims as the "second teacher", Aristotle being the first. He was most famous for his works on political theory and died in 950 A.D.

Ibn Sina (Avicenna), who died in 1037 A.D., was probably the most influential of all Muslim philosophers on the later development of Islamic philosophy and theology.

Ibn Rushd (Averroes), a Spaniard who died in 1198 A.D., was known mainly for his commentaries on Aristotle.

al-Tusi, who died in 1273 A.D., is not so well in the West but was very influential in the later development of Islamic philosophy.

I should like to point out here that many of the works of these Muslim philosophers were translated into Latin and Hebrew and had a profound influence on the development of philosophy among Christians and Jews.

Let me now turn to the basic ideas and doctrines which were common to most of the Muslim philosophers without, however, going into any of the differences which existed between individual philosophers.

(Divisions of philosophy)

First of all, Islamic philosophy covered a much wider range of subjects than we would consider to be included within philosophy today. According to al-Khuwarizmi,(1) a tenth century encyclopaedist, philosophy was divided into two major branches: theoretical and practical. Each of these branches in turn consisted of three subdivisions. Thus theoretical philosophy was made up of:

1. Metaphysics or theology, which dealt with non-material things.

2. Mathematics, which had to do with things existing both in the mind and in matter, and included arithmetic, geometry, astronomy, music, and mechanics, and

3. Physics, which dealt with material things, and included such sciences as medicine, meteorology, mineralogy, botany, zoology, chemistry, and finally psychology or the science of the soul.

The three subdivisions of practical philosophy were:

1. Ethics, that is, individual or personal ethics.

2. Economics, which in those days meant household or family ethics, and

3. Politics, which could be said to be the ethics of the city or the state.

Logic, which was the basis for all of these sciences, both theoretical and practical, was sometimes considered a third major branch of philosophy.

A much simpler division of philosophy into six main categories is given by al-Ghazali, an eleventh century theologian who studied philosophy and later wrote a book attacking many of its doctrines. Al-Ghazali divides philosophy into mathematics, logic, physics, theology or metaphysics, politics. and ethics.(2)

In this lecture I shall be speaking mainly about the metaphysics of Islamic philosophy since metaphysics is usually considered its most important subject as well as the subject which comes most into conflict with the Islamic religion. I shall also have something to say about physics and especially psychology, which was considered a subdivision of physics.

(Proof for the existence of a First Cause)

Works on metaphysics usually begin with a proof for the existence of a First Cause or Necessarily Existent Being. To prove the existence of this First Cause, the philosophers divided existence into three categories:

1. Necessary existence, which is predicated of that which does not need a cause for its existence,

2. Possible or contingent existence, which is predicated of things which can conceivably either exist or not exist, but which must have a cause if they are to exist, and,

3. Impossible existence, which is predicated of things whose existence would involve a logical contradiction.

The philosophers then argued that since possible or contingent things are known to exist, they must all have causes which have brought them into existence. If these causes are also possible or contingent, they in turn must have causes. However, since both an endless chain of causes and a circular string of causes are, according to the philosophers, impossible, any series of causes and effects must end with a first cause that itself does not have a cause for its existence. This first cause, then, must exist necessarily, that is, it must be a necessary existent since it exists, but does not have a cause for its existence. It is, as it were, its own cause. They further said that this first cause could not have any of the attributes of things that had causes for their existence, such as composition. It must be absolutely simple and not composed of parts, for if it were composed of parts then it would need a cause to bring the parts together.

(Proof that there is only one Necessarily Existent Being)

Having proven that a Necessarily Existent Being exists, the philosophers then proceeded to show that there can be only one such Necessarily Existent Being. This they did by supposing the existence of two necessarily existent beings. These two beings would be either exactly alike in every respect, or else they would differ from each other. If they were exactly alike in every respect, then there would be no way of distinguishing one of them from the other, and one would have to conclude that they were in fact one and the same being, not two separate beings. If, however, they differed from one another in some respect, then each one could be said to consist of at least two parts. One part in each would be that aspect of each in which they were alike, namely that they were both necessarily existent beings, and the other part would be that aspect in which they differed. Both, then, would therefore be compounded of two parts, and since anything compounded must have a cause for its composition, both, therefore would have causes and could not be necessarily existent beings.

Having shown that there was only one first cause or necessarily existent being, the philosophers went on to show that this First Cause, which they now equated with God, was not subject to change, that He was not subject to extinction, that He was not a body, that He was not located in time or space, and so on. These properties they called negative or privative attributes.

(Positive attributes of God)

The philosophers also ascribed seven positive attributes to the First Cause, maintaining that He was knowing, powerful, living, willing, speaking, seeing and hearing. These were the same attributes that the Islamic theologians also ascribed to God. The philosophers, however, gave these attributes an interpretation quite different from that of the theologians. In the first place, these attributes do not affect the essential unity and simplicity of the First Cause since they are not superadded to or an augmentation of His essence. On the contrary, they are actually identical with His essence.

How, then, did the philosophers explain these attributes in order to show that in actuality they were all identical with God's essence? I cannot now go into all the details of their explanation, but in effect what the philosophers said was that each one of these seven attributes was in reality just one aspect of the attribute of knowledge. And they then went on to show that God's knowledge was identical with His essence.

Their explanation was as follows: First of all, they defined knowledge of a thing as the immaterial form or image of that thing as it exists in the mind. Knowledge of a concrete or material object requires that a mental form or image of that thing be abstracted from the object. It is only through this mental form or image that a material thing can be known and it is this immaterial or mental image that is called knowledge by the philosophers.

Knowledge of an immaterial object, however, does not require that a mental image be abstracted from it, since immaterial or intellectual things can enter the mind directly without first having to be abstracted from matter. Thus, anything which is immaterial, such as God or the human rational soul, automatically knows itself, and, moreover, knows itself through itself rather than through a mental image of itself as is the case with material objects. In the case of immaterial beings, therefore, knower, known and knowledge are all reduced to one single entity. Thus, God, being an immaterial being, knows Himself through a knowledge which is Himself, and His knowledge cannot, therefore, be said to be superadded or additional to His essence, and thus God's absolute oneness is not in any way compromised.

The philosophers also asserted that God knows the universe as well as Himself. This is so, they said, because God knows Himself and he also knows Himself to be the cause of the universe. Then, on the basis of their doctrine that knowledge of a cause yields knowledge of all of its effects, they claimed that God knows the whole universe and everything in it since He is the cause of it all. Thus, even God's knowledge of what is other than Himself is reduced to His knowledge of Himself.

Nevertheless, since God does not know the universe directly but only by means of His knowledge of His own essence, which is the cause of the universe, and because His essence is not subject to change, it is impossible for Him to know particular things insofar as they are related to time. For example, He cannot know whether a particular thing exists now, or whether it no longer exists, or whether it is yet to come into existence, for if He possessed this type of knowledge about something, His knowledge of it would change with the passing of time. This, however, is impossible, since God's knowledge is identical with His essence and His essence is not subject to change. As I shall point out later, this question of God's knowledge of particular things in time was one of the principal areas of conflict between philosophy and religion.

As I mentioned previously the philosophers reduced the other six attributes of God to the attribute of knowledge. And so from their point of view all seven of God's attributes were the same as His essence.

(The Universe: Emanation theory)

Now having shown that the First Cause, or God, exists, and that He is qualified by these attributes without his unity being in any way impaired, the philosophers went on to explain how the universe came into being as the effect of the First Cause.

They said, first of all, that the universe as a whole must be eternal, that is, that it did not come into existence at some point in the past because God wished to create it at that time as was the position of the Islamic theologians. The philosophers asserted that since an effect or result cannot temporally lag behind its cause, if that cause is complete in every respect, then the universe as a whole, being the effect of the First Cause, could not temporally lag behind the First Cause and since the First Cause is eternal and has always existed, its effect, the universe, must also be eternal.

The philosophers then went on to say that since the First Cause is absolutely one, it can only be the cause of a single and indivisible effect, since any duality or multiplicity in the effect would imply duality or multiplicity in the cause, and this is impossible with respect to the First Cause. Consequently, this first effect cannot be a body, because bodies are compounded of matter and form, but must on the contrary be an immaterial substance. This first effect the philosophers called the First Intelligence or Intellect. Now this first intelligence, even though it is one, has, nevertheless, three aspects. First, it has knowledge of its cause, that is, of God. Second, it knows itself, and third, it knows itself as the effect of the First Cause. They then went on to say that from each one of these three aspects there results an effect. From the first aspect there results a second intelligence, from the second aspect is produced a soul, and from the third aspect a body, and this body is identified with the outermost of the nine concentric spheres of the Ptolemaic universe.

The second intelligence in turn has three aspects from which result a third intelligence, a second soul, and a second body, which is the body of the eighth sphere, or that of the fixed stars. This series of effects continues on to the tenth intelligence, the ninth soul, and the ninth body which corresponds to the sphere of the moon. The tenth intelligence is known as the active intellect, and has an important role to play in the human perception of universals and first principles. Each of these nine bodies corresponds to one of the Ptolemaic concentric spheres, so that starting from the Earth at the center of the universe we have first the sphere of the moon, corresponding to the ninth body, then the sphere of Mercury, then that of Venus, then the Sun, Mars, Jupiter, Saturn, the fixed stars and finally the outermost sphere surrounding the entire universe. Because they are made of ether, which is transparent, these nine spheres are invisible. Only the planets and stars contained within the spheres can be seen.

Below the sphere of the moon is the world of matter, which is made up of the four elements, fire, air, water and earth, and at the very center of this world of matter is of course, the planet earth. The four elements of the material world are all subject to the process of generation and corruption, which is brought about by the influence of the seven planets. As a result of this process of generation and corruption three classes of compound bodies are produced, namely, minerals, vegetables, and animals. The class of animals, of course, reaches its culmination in human beings.

(Psychology)

Now the mention of human beings brings us to the subject of psychology, that is, the science of the human soul. According to the philosophers, human beings are made up of body and soul. The human soul consists of three degrees or levels. The first is the vegetable or plant soul which is responsible for nourishment, growth, and reproduction, and which is common to both plants and animals. The second is the animal soul, which is the cause of movement and the perception of particular objects through the five senses; and the third is the rational soul, by which human beings are able to perceive universal concepts and to think logically by using those concepts in statements and propositions. The rational soul is possessed only by human beings, and it is this rational soul which distinguishes humans from other animals. Moreover, the rational soul, unlike the plant and animal souls, is immaterial, as well as simple and indivisible. As such it is not subject to corruption and is therefore immortal. One of the principal functions of the rational soul is the abstraction of universal concepts from particular concrete objects. It does this with the help of a kind of spiritual light which emanates from the active intellect, which you will recall is the tenth intelligence in the series of intelligences emanating from the First Cause. This spiritual light enables the rational soul to perceive correctly the universal concepts embedded within particular concrete objects.

Because he possesses this rational soul, a human being stands, as it were, half-way between the sublunary world of matter and the elements, on the one hand, and the world of intelligences and God, on the other. His body links him to the world of matter, but by means of his rational soul or intellect he is capable of coming into contact with the active intellect and the other intelligences. The goal of a human is to develop and perfect his rational soul through reasoning and the contemplation of the intelligences and God, so that he gradually becomes less and less dependent on his body and the world of matter, and increasingly involved and absorbed in the contemplation of God the intelligible world. The desires and pleasures of the body are thus gradually left behind and enjoyment and happiness are more and more derived from intellectual and spiritual pursuits. Accordingly, the perfect man is the one who has completely freed his soul from attachment to the body and its desires, and who is totally absorbed in the contemplation of God. Such a man has attained true happiness, and at the time of death will not be adversely affected by the loss of his body, since pain and misery after death are suffered only by those who still retain some attachment to the body.

(Ibn Sina on the perfection of the soul)

The philosophers are somewhat vague when it comes to describing just what this state of perfection is, and just how far towards perfection a soul must have progressed in order to attain happiness and avoid misery after death. Ibn Sina in his Kitab al-Najah (English: Book of Salvation) has the following to say on this point:

"As for the question how far the human soul needs to be capable of conceiving intelligible abstractions, so that it may pass beyond the point where this misery is bound to befall, and in transgressing which that happiness may be justly hoped for; this is a matter upon which I can only pronounce approximately. I suppose this position is reached when a man achieves a true mental picture of the incorporeal principles, and believes in them implicitly because he is aware of their existence through logical demonstration. He is acquainted with the final causes of events happening in universal (not partial), infinite movements; he has a firm grasp of the disposition of the All, the mutual proportions of its parts, and the order pervading the Cosmos from the First Principle down to the remotest beings, all duly arranged. He can apprehend Providence in action, and realizes what kind of being belongs exclusively to the Essence Preceding All, what sort of Unity that Essence possesses, how that Essence achieves cognition without any consequent multiplicity or change of any kind, in what manner other beings are related in due order to that Essence. The clearer the inward vision of the speculative becomes, the more fully qualified he is to attain supreme happiness. A man will hardly free himself from this world and its entanglements, except he be more firmly attached to the other world, so that his yearning to be gone thither and his love for what awaits him there block him from turning back to gaze at what lies behind him."(3)

The practical branches of philosophy, that is, ethics, economics, and politics, deal with the means by which all humans in a society can achieve this perfection, free themselves from the world of matter, and thus attain to supreme happiness after death.

These then, in a very brief and summary form, are the basic beliefs of the Islamic philosophers. Theoretically, at least, their beliefs are based entirely on reason and the information gained from sense perception. There is no place in their system for divine revelation and prophecy, since the attainment of perfection and supreme happiness is possible for anyone who is willing to use his own reason and develop his own intellect to that end.

(Prophecy)

One of the Islamic philosophers, al-Razi, who, as I mentioned before, died in 923 A.D., was outspoken in his rejection of revealed religion and prophecy. Al-Razi defended his rejection of revealed religions as follows: In the first place, he said all revealed religions, such as Christianity, Judaism and Islam were based on their own sacred scriptures. Now if these scriptures have all come from God, then they should not contradict each other, since it is inconceivable that God would contradict himself. Nevertheless, when we examine these scriptures and compare them we find that they do in fact contradict each other. Now from this we can conclude either that all these scriptures and the religions based on them are false, or that one of them is true and the others are false. Then he goes on to ask: if one of them is in fact true, how can we tell which one it is? And he answers by saying that, since God cannot contradict himself then a true religion, based on a scripture actually revealed by God must be a religion which contains no contradictions in its scripture. However, he goes on to say, if we examine all of these revealed scriptures, we find each one contains contradictions. Therefore all of these sacred scriptures along with the religions based on them must be false.

Al-Razi had other arguments as well against revealed religions, and one of these concerned the need for revelation and prophecy in the first place. Al-Razi had a firm belief that human reason was sufficient to tell us how to behave and what to believe in. What a prophet says, then can either agree with what reason has already told us or can tell us, and in this case we do not need a prophet to tell us what we already know, or else what a prophet says does not agree with reason, and we must, in that case, as rational beings, reject it, otherwise we lower ourselves to the level of non-rational beings or animals.

Some of the other Muslim philosophers, like al-Farabi and Ibn Sina, however, faced with the fact that religions did exist, tried to find some sort of rational explanation for them. Ibn Sina, in fact, even argues that prophecy and revelation are a necessity. His argument, given in his Kitab al-Najah(4), is as follows:

He says, first, that a man cannot live in isolation from his fellow men, but must, for his own welfare and happiness, live in a society in which he cooperates with others. Now a society cannot function properly unless it is regulated by a code of laws, and it is therefore necessary that there be a lawgiver to communicate these laws to society. And this lawgiver must be a human being, since only a human being can communicate with other humans. On the other hand, this lawgiver cannot himself formulate these laws, because, since men differ in their opinions, there would be no reason why men should accept his laws rather than the laws of some other lawgiver. Therefore, the lawgiver must be divinely inspired, that is, he must be a prophet, and in addition, he must have some distinguishing feature so that men will know for sure that he IS divinely inspired. And this distinguishing feature is his power to perform miracles.

Then, in order to get people to obey this divinely inspired law, the prophet must present the law in conjunction with a simple religious system. He must, for example, establish a belief in one God, who is the creator of the universe, as well as a belief in an afterlife in which men will be rewarded or punished by God depending on whether or not they have obeyed or or broken the law which the prophet has given them. He must also establish a religious ritual which people are required to perform repeatedly and at short intervals in order to keep them from forgetting the law and the religious beliefs supporting it.

Moreover, these religious beliefs must be stated in very simple terms, and with much use of symbols and parables, so that they can be easily understood by anyone. Let me quote to you what Ibn Sina had to say in this respect. He says:

"It is not necessary for him (that is, the lawgiver) to trouble their minds with any part of the knowledge of God, save the knowledge that He is One, True, and has no like; as for going beyond this doctrine, so as to charge them to believe in God's existence as not to be defined spatially or verbally divisible, as being neither without the world nor within it, or anything of that sort -- to do this would impose a great strain upon them and would confuse the religious system which they follow already, bringing them to a pass wherefrom only those rare souls can escape who enjoy especial favour, and they exceedingly uncommon. The generality of mankind cannot imagine these things as they really are except by hard toil; few indeed are they who can conceive the truth of the Divine Unity and Sublimity. The rest are soon apt to disbelieve in this sort of Being, or they fall down upon the road and go off into discussions and speculations which prevent them from attending to their bodily acts, and often enough cause them to fall into opinions contrary to the good of society and inconsistent with the requirements of truth. In such circumstances their doubts and difficulties would multiply, and it would be hard indeed by words to control them; not everyman is ready to understand metaphysics, and in any case it would not be proper for any man to disclose that he is in possession of a truth which he conceals from the masses; indeed, he must not allow himself so much as to hint at any such thing. His duty is to teach men to know the Majesty and Might of God by means of symbols and parables drawn from things which they regard as mighty and majestic, importing to them simply this much, that God has no equal, no like and no partner."(5)

Now this gives us a philosophical justification for the existence of prophets and revealed religion. It does not, however, tell us anything about the relationship between religious doctrines as revealed in sacred scriptures on the one hand, and philosophical doctrines arrived at through rational demonstration on the other. If philosophical beliefs and religious beliefs conflict and contradict each other, which beliefs can be accepted as true? If we accept as true philosophical beliefs which have been proven rationally, can we also accept religious beliefs as true, especially if they contradict our philosophical beliefs?

What answers did the Islamic philosophers have for these questions? As I mentioned previously, al-Razi rejected all religious beliefs as false and so was not interested in reconciling them with philosophical beliefs. The other Islamic philosophers, such as al-Farabi, Ibn Sina, Ibn Rushd and Ibn Tufayl, however, sought to reconcile religious doctrine with their philosophical beliefs. They did this through the use of allegorical interpretation. That is, they interpreted all religious beliefs which contradicted their philosophical beliefs in such a way as to make the religious beliefs agree with their philosophical beliefs. Those of you who are familiar with the writings of the Islamic theologians will recall that they also made use allegorical interpretation to deal with the contradictory doctrines that they found within Islamic scripture.

Before I close, let me read a passage on allegorical interpretation from a work by Ibn Rushd called Fasl al-Maqal (English: The Decisive Treatise).

"Now since this religion (that is, Islam) is true and summons to the study which leads to knowledge of the Truth, we the Muslim community know definitely that demonstrative study does not lead to conclusions conflicting with what Scripture has given us; for truth does not oppose truth but accords with it and bears witness to it."

"This being so, whenever demonstrative study leads to any manner of knowledge about any being, that being is inevitably either unmentioned or mentioned in Scripture. If it is unmentioned there is no contradiction, and it is in the same case as an act whose category is unmentioned, so that the lawyer has to infer it by reasoning from Scripture. If Scripture speaks about it, the apparent meaning of the words inevitably either accords or conflicts with the conclusions of demonstration about it. If this apparent meaning accords there is no argument. If it conflicts there is a call for allegorical interpretation of it. The meaning of allegorical interpretation is: Extension of the significance of an expression from real to metaphorical significance, without forsaking therein the standard metaphorical practices of Arabic, such as calling a thing by the name of something resembling it or a cause or consequence or accompaniment of it, or other things such as are enumerated in accounts of the kinds of metaphorical speech."(6)

For philosophers like Ibn Sina and Ibn Rushd, religious doctrines were true and did not, at least when interpreted correctly, contradict philosophical truths. The apparent contradictions between revealed truth and philosophical truth were due to the necessity of presenting truth to the masses in a simplified and symbolic form that they could easily understand. The Qur'an, then, can be understood, as it were, on two levels. It can be accepted literally, and this is the way the ordinary man without philosophical training is expected to accept it, and it can also be understood allegorically and in complete harmony with philosophical truth.

(Reaction against philosophy: al-Ghazali and others)

As might be expected many Muslims were not willing to accept this idea of the philosophers that revealed religion was merely an allegorical or metaphorical version of philosophy and that any passage in scripture that did not agree with philosophy could be interpreted allegorically to agree with philosophy.

Al-Ghazali, a Muslim theologian who died in 1111 A.D., wrote a work called The Incoherence of the Philosphers (Arabic: Tahafut al-Falasifah) in which he attacked their beliefs and doctrines. In it he listed 20 philosophical doctrines which he claimed contradicted the tenets of the Islamic faith and which must therefore be considerd erroneous. On account of 17 of these doctrines, he claimed that the philosophers must be considered heretics, and on account of three of them they must be considered infidels, since these three points are in complete disagreement with the beliefs of all Muslims regardless of their sect.

These three philosophical doctrines were the following:

1) The philosophers' claim that the universe is eternal rather than originated in time.

2) Their assertion that Divine Knowledge does not encompass knowledge of individual objects or particulars in time.

3) Their denial of the resurrection of bodies.

Concerning these three doctrines al-Ghazali says:

"These three doctrines are in no way in harmony with Islam. To believe in them is to believe that the prophets lied, and that what they taught was [a form of metaphorical] representation (tamthil) and indoctrination (tafhim) for the benefit of the masses. And this is clear infidelity to which no Muslim sect would subscribe."(7)

The controversy between philosophy and Islamic theological beliefs did not end with Ghazali's attack on philosophy in his Incoherence. Ibn Rushd, who died in 1198 A.D., wrote a reply to Ghazali's work which he called The Incoherence of the Incoherence Arabic: Tahafut al-Tahafut). Later Fakhr al-Din al-Razi, a famous Muslim theologian who died in 1209 A.D. wrote a commentary on Ibn Sina's al-Isharat wa-al-Tanbihat (English: Indications and Admonitions) in which he argued against the doctrines of the philosphers. His arguments against philosophy were in turn answered by Nasir al-Din al-Tusi, a philospher who died in 1273 A.D., in his own commentary on Ibn Sina's Isharat. Thus, although condemned by many Muslim theologians, philosophy continued to appeal to many other Muslim thinkers.

1. See his Mafatih al-`Ulum, Cairo 1342, pp. 79-80.

2. See his al-Munqidh min al-Dalal, Watt translation, pp. 33-38.

3. See A.J. Arberry, Avicenna on Theology, pp. 71-72.

4. See pp. 303 ff. of the Arabic text, and pp. 42-44 of Arberry's Avicenna on Theology.

5. See Kitab al-Najah, Arabic text, p. 305; Arberry, Avicenna on Theology, p. 44.

6. See Hourani's translation, p. 50.

7. See Tahafut, English translation, p. 249; Arabic text, p. 376.

Arberry, A.J., Avicenna on Theology. London 1951. The Wisdom of the East Series.

al-Ghazali, Abu Hamid Muhammad ibn Muhammad, al-Munqidh min al-Dalal. Translated by W. Montgomery Watt in The Faith and Practice of al-Ghazali. London 1953.

al-Ghazali, Abu Hamid Muhammad ibn Muhammad, Tahafut al-Falasifah. Translated by Sabih Ahmad Kamali under the title: Al-Ghazali's Tahafut al-Falasifah [Incoherence of the Philosophers]. Lahore 1958.

al-Ghazali, Abu Hamid Muhammad ibn Muhammad, Tahafut al-Falasifah. Edited by Maurice Bouyges. Beirut 1927.

Ibn Rushd, Abu al-Walid Muhammad ibn Ahmad, Fasl al-Maqal. Translated by George F. Hourani under the title Averroes on the Harmony of Religion and Philosophy. E.J.W. Gibb Memorial Series, New Series, XXI, London 1961.

Ibn Rushd, Abu al-Walid Muhammad ibn Ahmad, Tahafut al-Tahafut. Translated by Simon van den Bergh. Two volumes. E.J.W. Gibb Memorial, London 1954.

Ibn Sina, Abu `Ali al-Husayn ibn `Abd Allah, al-Najah fi al-Hikmah al- Mantiqiyah wa-al-Tabi`iyah wa-al-Ilahiyah. Cairo 1357/1938.

Ibn Sina, Abu `Ali al-Husayn ibn `Abd Allah, al-Isharat wa-al-Tanbihat. With the commentaries of Nasir al-Din al-Tusi and Qutb al-Din al-Razi. Three volumes. Tehran 1377-1379.

al-Khuwarizmi, Muhammad ibn Ahmad, Mafatih al-`Ulum. Cairo 1342.