Natural philosophy written in Arabic from the time of the Koranic message through the 7 AH/13 CE century is the subject matter of the entry. It consists of an introduction and two chapters: the first examines the thinkers of the kalām tradition, i.e., rational defenders of Islamic dogmas, and the second, the falāsifa, whose ideas are grounded on the Greek philosophy and science. Within each entry, the order is chronological.
Introduction
Islamic philosophy does not have a unique doctrine about nature and physical issues but has common features. Two main streams flow in a related direction: the kalām tradition mostly assumes that substances are bodies made of atoms; the falsafa distinguishes between sensible and immaterial substances and assumes substances are bodies that can be infinitely divided.
Under the influence of Greek philosophy, falsafa develops a deeper and more comprehensive explanation of nature. It conflicts with kalām on the issue of the pre-eternity of the universe, because the mutakallimūn understand that eternity in the past excludes the causal action of a free agent. Although this is an important issue, it is not the only one.
The condemnation of Averroes in Almohad times and occasional burnings of philosophy books, including Avicenna’s, should not make us believe that falsafa was ousted from Islamic learning. Many Islamic thinkers, such as al-Baydawī (d. 1316?), did not see any conflict in studying kalām and falsafa at the same time. They were abiding by the Qurʾānic teaching to contemplate and reflect on nature.
اَلرَّحۡمٰنُ. عَلَّمَ الۡقُرۡاٰنَ. خَلَقَ الۡاِنۡسَانَ. عَلَّمَہُ الۡبَیَانَ. اَلشَّمۡسُ وَ الۡقَمَرُ بِحُسۡبَانٍ. وَّ النَّجۡمُ وَ الشَّجَرُ یَسۡجُدٰنِ.
The Merciful taught the Qurʾān
Created man,
Taught him the explanation,
The sun and the moon are in a reckoning,
The star and the tree do obeisance (Qurʾān
55:1–5).
The Qurʾān’s cosmological model consists of the seven heavens and seven earths that we also find recorded in the Bible and in ancient Mesopotamian texts; the heavens are built up on a flat earth [Qurʾān 65:12]. However the Qurʾān is obviously not a treatise on nature, and its doctrine aims at man and at his behavior. God instructs man how to do good and avoid evil, and He shall punish or reward him in the afterlife for his bad or good actions. This is possible not only because of His omnipotence but also because of His goodness toward man. Man has to show Him gratitude for the goodness; one way to show Him gratitude is by contemplating creation, which reveals to us His omnipotence as well as His intelligence.
Therefore, Muslims who were interested in knowing the secrets of nature have to abide by some principles. There is one God who is almighty. He not only created the world but He also intervenes in its daily activity. Moreover, He may be the real agent of events, which appear to be the work of human agents.
Islam expanded as Muslims conquered many lands in a short time period; Muslims thus entered into contacts with other religions and civilizations. Present Iraq was under Sasanian rule, but its population consisted of Arameans, Persians, and Arabs. The official religion of the Sasanian Empire was Zoroastrianism, which was practiced by many Persians, although some were Christians. Jews and Christians were
strong in Mesopotamia, and most of them spoke Aramaic dialects. Arabs immigrated to Iraq since the Parthian period when Arabs organized border states. They were sedentary as well as nomads; the former converted mainly to Nestorianism.
The Muslim conquest brought new Arab populations into Iraq, and new cities were founded where they settled. Kufa (founded in 638) and Basra (founded in 635) are the most representative cities, and together with an enlarged Baghdad, they became centers where arts and sciences flourished over the years.
In the first-century Hijra/seventh CE, Basra was a center of Qurʾānic studies. There were early Basrians who knew the various readings of the Book and the traditions of the Prophet (Pellat 1953). In the first century, discussion on religious issues began, including whether or not a capital sinner is any longer a Muslim. In addition, the Basrian population was acquainted with foreign cultures and their scientific creations.
Philosophy of Nature in the Kalām Tradition
The science of kalām (علم کلام), that is, rational explanation of the Islamic dogmas, developed later in the second-century Hijra. However, the kalām was not the only discipline aiming at rational explanations. The theologian and heresiograph al-Ashʿarī (d. 935) occasionally mentions those “who sustain the natures,” aṣḥāb al-ṭabā’i ʿ. “Natures” were the four principles (hot–cold–humid–dry) of the four elements following the Aristotelian tradition (fire–air–water–earth). These people should be considered as the first philosophers of nature who were active in Iraq, mainly in Basra, already in the second-century Hijra/eighth century CE. Van Ess identified several of them, the most important being Muʿammar Abū l-Ashʿath.
The third/ninth century is the time when the Muʿtazila shaped kalām developing it into a philosophical system and comprehending the study of the Divine essence, His creation of the world and natural reality, and man and his moral responsibility. Muʿtazila is the plural of Muʿtazilite and means the “Separatists,” those who separated themselves from something. Nallino produced evidence that the word meant separation from those religious parties that fought each other with the sword. However, the meaning remains a matter of discussion. Two men are named as the founders, Wāṣil ibn ʿAṭā’ (d. 749) and ʿAmr ibn ʿUbayd (d. 760) who lived in Basra. The textual evidence shows that both were interested in theological and political matters, not in philosophical ones.
We find the first references to ontological issues in Abū Bakr ʿAbd al-Raḥmān al-Aṣamm (d. 816). Al-Ashʿarite quotes al-Aṣamm: “I only affirm the three-dimensional body” so that he denied movement, rest, and other accidents of the bodies. We have more information about Abū ʿAmr Ḍirār ibn ʿAmr (d. 796) and his doctrines on physical reality. He affirmed that accidents, aʿrāḍ, first build a body, and then the body becomes the bearer of accidents. Accidents mean physical properties:
Body is accidents which are put together and joined so that they stand and are permanent. Then they become a body which bears the accidents; once it settles down, it bears the accidents and changes from one state into another. Bodies cannot exist without accidents or their contraries. For instance, in life and death, not a single body can exist without one of them, and none of its kind can be separated from colors and tastes nor from weight, as heaviness and lightness, nor from coarseness and softness, nor from warmth and coldness, nor from humidity and dryness, nor from resistance.
Ḍirār seems to have supported two theses: bodies are made out of accidents, and bodies bear accidents of which bodies cannot be deprived of (unless they are destroyed). The doctrine looks rather contradictory, but we should not forget that the information is supplied by al-Ashʿarī, who lived almost two centuries later and who reports only fragments or phrases ascribed to the authors he mentions.
The main point is that bodies are defined by the accidents they bear. Abū ʿAmr Muʿammar ibn ʿAbbād al-Sulamī (d. 830) built a system which we can better reconstruct. He lived in Basra and was in touch with Maʿmar Abū l-Ashʿath. Muʿammar was a pharmacist, which may explain his interest in the physical constitution of bodies. He appears to have been the first person to expound atomism. Atomism became the most original contribution of the Basrian rationalists. Muʿammar admits that the body is something three-dimensional, but he adds the reason: its atomic composition. The best known definition reads:
[The body] is that which is long, wide, and deep. Bodies consist of at least eight parts. When the parts are reunited, accidents are generated, and they are caused by the force of nature. Each part produces accidents that inhere to it. He affirmed that length is produced when one part is joined to another one; width is produced when both are joined to other two parts; and depth is produced when the four are applied to other four parts. Therefore, eight parts comprise a three-dimensional body.We may, therefore, see the atom as some kind of substance, but the real, effective substance is the body, which is composed of eight atoms. From the body, accidents will result. The substance “body” cannot be perceived; only accidents are perceived. Colors and tastes, odors and sounds, warmth and coldness, and humidity and dryness are accidents; Muʿammar adds movement and rest. God does not intervene directly in the events and activities of creatures; instead, He uses an instrument – bodies. Giving life and bringing death are caused by God but also natural color.
Muʿammar looked for a scientific explanation of nature. This search led him to recognize capacities in the bodies, which moved thanks to them; also, these capacities caused effects in a regular way. He introduced the concept of maʿnā, to explain movement in particular. Maʿnā is commonly translated as “meaning”; but, when Muʿammar says that movement and rest in a body differ because of a maʿnā, a notion of cause is implied. Muʿammar establishes an endless chain of maʿānī residing in bodies. Wolfson saw in the doctrine of endless maʿānī a way to integrate Aristotle’s doctrine of nature with its eternal motion.
Abū l-Hudhayl Muḥammad ibn al-Hudhayl al- ʿAllāf (d. 841) was originally from Basra, but he succeeded in entering the court of the Caliph al-Ma’mūn. He is the major representative of Muʿtazilite atomism. Atoms do not have dimensions; if six of them touch each other, a body results. The body has three dimensions and six directions: right and left, back and front, and top and bottom. We should not imagine any geometrical figure because the smallest “touchable” body needs 36 atoms, that is, six sets of minimal bodies. Atoms can move or rest, join others, or separate from others, but they cannot have colors and tastes, or life, or knowledge. As for the possibilities of movement, there was a discussion whether an atom can have two movements, and Abū l-Hudhayl al-ʿAllāf did not accept this notion. Although one stone is moved by two different movers, the movement is one for it:
Abû l-Hudhayl taught: like there is one movement divided into two agents, there is also one movement of many atoms, and two different actions. He claimed that accidents divide in time and place, according to the two agents. He also claimed that the movement of the body divides according to the number of its atoms, as does its color. The part of movement which affects this atom is different from the part of movement which affects that atom.
Time is an accident, but it does not reside in a body; Abū l-Ḥudhayl does not explain what place is. When an atom moves on a surface, it reduces the distance covering or touching each atom of the surface. No doubt, movement and rest are major issues of the atomistic doctrine. Bodies move at different speeds, and Abū l-Ḥudhayl explained that not all atoms get movement at the same time. Some get rest, so that speed is the ratio between atoms endowed with movement and those with stops. A body is at complete rest when all of its atoms have the accident of rest. The difficulties of the atomic idea of reality were obvious to his relative and disciple Abū Isḥāq Ibrāhīm al-Naẓẓām (d. c. 845). Al-Naẓẓām objected that if atoms have sides, then they must be divisible. Bodies are not made of atoms:
Body is length, width and depth. Its parts do not have a number by which you can stop; not a half, from which a half can be given, not a part from which another part can be given. The philosophers define the body as width and depth.
Accidents are the elements of substance, except for movement. Al-Naẓẓām raised many objections to the atomistic theory of motion. He believed that movement happens in a discontinuous space, through leaps. If movement were continuous over infinite atoms, even if it were possible, one object could not run faster than another. His best-known argument is that of the square and two ants. The ant going on the diagonal shall arrive at its goal before the ant going on the legs of the triangle. Al-Naẓẓām argues as if he accepts the atomic structure: the ant going on the diagonal or hypotenuse “jumps” over a smaller number of atoms than the ant “jumping” over the atoms of the legs. The atomists, represented by Abū l-Hudhayl, reacted against his criticism, and the discussion was continued by Ibn Ḥazm, Shahrastānī, and Fakhr al-Dīn al-Rāzī, theologians who opposed atomism.
Another important notion of Naẓẓām’s physical doctrine is latency, kumūn, which he shares with other Muʿtazilites: “Abūl Hudhayl, Ibrāhīm [al-Naẓẓām], Muʿammar, Hishām ibn al-Ḥakam, and Bishr ibn al-Muʿtamir taught: oil was in the olive, ointment was in the seed of sesame, and fire was in the stone”. Al-Naẓẓām stressed the importance of fire for life. If we take into consideration what his contemporary al-Jāḥiẓ (d. 869) wrote about him, fire was for him more important that other elements, like water and earth.
Latency points to the nature of bodies and physical entities. They contain a mixture of elements; while one shows up, the rest is hiding in the substance. The doctrine is opposite to the continuous creation of events by God, but we do not know the necessary details. We expect that al-Naẓẓām establishes the order about how effects appear. In a general sense, his doctrine reminds the Aristotelian doctrine of potency and actuality. About a century later, Abū Hāshim ibn al- Jubbā’ī (d. 933), the son of a Muʿtazilite master, Abū ʿAlī al-Jubbā’ī (d. 916), introduced the doctrine of states or modes, aḥwāl, in the course of the discussion on divine attributes.
Abū Hāshim distinguished between caused and uncaused states. Caused states include “living” in a creature, which has the maʿnā of life in itself, and uncaused states include the property of occupying a place or genera and species of the substance. Abū Ḥāshim ibn al-Jubbā’ī was a contemporary of Abū l-Ḥasan ‛Alī al-Ashʿarī (d. 935). Al-Ashʿarī was born in Basra but he spent most of his life in Baghdad. He remodeled kalām into a form acceptable to the orthodoxy in theological aspects.
Concerning cosmology, al-Ashʿarite followed his master al-Jubbā’ī who was a follower of Abū l-Hudhayl al-ʿAllāf: the universe consists of substances and accidents. Natural substances are atoms, and their aggregates build bodies. Accidents explain the variety of substances because the latter are homogeneous. Al-Ashʿarī classified accidents into various categories and formulated rules applying to them.
The accident kawn, “being,” belongs to the local category; by virtue of the accident “being,” any substance is situated in a place, and no substance can be devoid of the accident “being” in this sense. Place means a body or atom on which something relies, against which something leans, and one place suffices to be at rest; movement requires at least two places.
Two disciples of al-Ashʿarī, Abū Bakr al-Baqillānī (d. 1013) and Abū l-Maʿālī al-Juwaynī Imām al-Ḥaramayn (d. 1085), shaped the physical doctrine of Ashʿarite kalām. Al-Juwaynī argued that since an infinite number of accidents are impossible, there must be a beginning of all bodies. They both helped atomism triumph over al-Naẓẓām’s theory of the infinite divisibility of the body. Prevailing did not mean the end of the adversary school: we have instances of the latter doctrine in kalām authors such as Ibn Ḥazm (d. 456/1064). Ibn Ḥazm was influential during a short period of the Almohad dynasty (1121–1269) and to a limited extent.
Atoms, the void, and the possibility of other worlds are doctrines of Abū l-Faḍl Muḥammad Fakhr al-Dīn al-Rāzī (d. 606/1209). He was one of
the most important theologians of the Islamic postclassical period and embodied the Ash‘arite thought for this late period. The Sufi Ibn ‘Arabī regarded him as the leading philosopher of the time although he wrote him that mystical gnosis was superior to rational discourse. Fakhr al-Dīn al-Rāzī was a prolific author, his works encompassing the great Qur’ān commentary, his theology treatise The Acquired Thoughts, or his criticism of Avicenna’s Remarks and Admonitions and The Sources of Wisdom.
Al-Maṭālib al-Āliya, The Higher Issues, deals with theological as well as physical issues, and as A. Setia observed, the work represents his final thought and for this reason we are relying on it. There he defines being (mawjūd) either as that which occupies a place (ḥayyiz) or as that which is a condition or state (ḥāl) of what occupies a place or that which is neither of both and that is God.
If that which occupies a place is divisible, is a body, and if not, it is an atom. That which is a condition or state is an accident; besides the qualities related to the five corporeal senses, al- Rāzī counts kawn “coming-to-be” as accident. “Kawn is the expression of the fact that substance occurs in a place” and comprehends four categories: movement, rest, gathering, and disassembling. Among living beings we find exclusively the accidents of life and the attributes of knowledge and action.
Section V of The Higher Issues contains treatises on time and place: Our knowledge of time is a primary intuitive knowledge (‘ilm badīhī awwalī). Time is composed of successive instants that are indivisible; it is not a property of motion, but motion cannot be understood before one understands the essence of duration and time because motion implies occupying a place after being in another, and this is the definition of motion: leaving an occupied place and striving for another. Time is not a continuous quantity, as Aristotle and his followers assert, but a succession of instants and “the actual instant does not admit division”. He distinguishes between incidental time (zamān), endless time (sarmad), and unlimited time (dahr), and he explains as follows:
Plato’s opinion concerning time and duration is closest to ours. Time is a being subsisting by itself, autonomous by itself. If we consider its relation to the permanent beings free from change we call it endless time (sarmad), if we consider its relation to that which precedes motions or changes we call it unlimited time (dahr), and this is the very unlimited time, and if we consider its relation to the changing beings insofar as they are connected to it and occurring together with it, we call it time (zaman).
Al-Rāzī reports that the philosophers agree on the pre-eternity (qidam) of the sarmad, the endless time, and duration, while the theologians defend its innovated creation (ḥudūth), and he is among them. On place, al-Rāzī considers two views: one as expression of the matter or form and the other as the void; the second view comprehends the view of the theologians and some philosophers. He aligns with the theologians and maintains that place is “the distance called void” (faḍā’), an empty distance. Void is defined also as that which exists between two bodies that are not in touch. Rāzī refutes at length and with detail the arguments based on the impossibility of motion in the void and explains how the void plays its role in motion, for instance, when the fish moves in the water:
Our view is that plenty of void is produced in the water, and it is the cause why water is rare and waving although water is heavy and flowing by nature. Whenever some parts of water strive to some empty places, the other places become empty, and the parts of water strive again from their places to them, and so on indefinitely. For this reason, the body of the water is always waving and moving.
Section VI of The Higher Issues deals with first matter, and al-Rāzī knows two definitions, one says that it is the atoms and the other “a self-subsisting entity in which corporeity dwells”; he needs to analyze the conditions of the body in order to decide about the definition of the first matter.
Al-Rāzī opposes the definition of body of the Muʻtazilites to that of the philosophers. The former define a body as “the long, the wide and the deep” and the latter as “the substance in which the three dimensions can be determined, standing on right angles”. He relates the definitions to the issue whether the body is composed of atoms, and he examines the doctrines of the philosophers and the Kalam people in the following pages. This examination leads him to consider motion, and he summarizes:
We prove that motion is an expression of successive occurrences (ḥuṣūlāt) in contiguous places so that each one of these occurrences does not admit division at all. We also prove that time is composed of consecutive contiguous instants so that each one does not admit division at all. Then once this discourse on motion or on time is clear, we can prove with certainty that the body is composed of atoms.
Motion, therefore, is not something continuous admitting infinite divisibility, and he argues against it although he says that its falsity is known by obvious intuition (badīhīya). Al-Rāzī mentions Avicenna regarding the discussion about a stone thrown high into the air and then falling to the earth. Avicenna claimed that it is at rest for some time between the two motions, and al-Rāzī denies the possibility and defends the theory of successive instants.
Other examples are considered, and al-Rāzī wants to interrelate motion, time, and atoms. The sphere can only be in touch with a plain surface if there is an atom, an indivisible contact point, and on this basis he starts arguing for the existence of the substance that is one. Al- Rāzī says that he resorts to Euclid’s geometry and explains:
If we roll the sphere on the surface so that it completed its circle, there is no doubt that the contact never ceased, and the contact has occurred in another point, and there is nothing different between the two points because we speak only of the point in which the contact has occurred in the first instant of contact as the first point. According to this appraisal, the line is drawn by the assembling of points and if the line results from the assembling of points, likewise the surface results from the assembling of lines, and the body from the assembling of surfaces. The contact point in the sphere is not divisible, and the body results from the integration (inḍimām) of points, and that is intended by “single substance.”
Therefore, the point is something that exists, to which the senses can point to, and indivisible: it is the “single substance” (al-jawhar al-fard). From the single substance, al-Rāzī proceeds to the body which is composed of them and of a finite number. He refers, for instance, to the polemic between the atomist Abū l-Hudhayl al-ʿAllāf and his opponent al-Naẓẓām and the question of the leap and is definite in his affirmation of atomism. Arguments of geometrical kind abound in many chapters with references to Euclid or to Ibn al-Haytham.
“Aristotle’s followers” argued that the universe has a spherical shape and that is one alone because if there were two spheres, the void would exist between them and the existence of void is not possible, but al-Rāzī already asserted the opposite, namely, the existence of void. Furthermore he asks them: why the shape of the world must be spherical? The first body has the shape of a cube.
He puts more questions on the philosophers showing that there can be more than one world. He rejects the existence of first matter, although he accepts that “the body in itself is something one and continuous but continuity for us is simple unity”. Divisibility of a substance implies two substances; there is no option for an eternal first matter.
The new creation of the world (ḥudūth) should be mentioned as one of the fundamentals of al-Rāzī’s philosophy. The Divine Writings inform of the creation of the world, but they do not contain a clear affirmation that the world is newly created after its nonexistence. However if we look at Sect. I of The Higher Issues, we already meet “Those who affirm the anew creation of the world, are more than those who affirm its eternity and besides the majority maintains that He be Exalted became agent of the world after He was not agent of it”. He was careful to give all arguments, against and in favor of the anew creation, but he sided with the Muʻtazilite doctrine.
An entire chapter of Sect. I of The Higher Issues summarizes his view of the universe. Every celestial sphere has a given quantity and density (kathāfa). Every sphere is composed of parts as any other substance. Motion and rest are equally possible in all these bodies, as different velocities also are. The spheres are different from the stars embedded in them, and the stars take a determined point in them.
F. al-Rāzī uses the term jā’izāt, “thinkable objects,” to refer to this possible character and to oppose absolute necessity concerning the number or details of the spheres. He reminds that the existence of the void was proved and adds that it is endless, existing outside the sphere, and that this occupies just one part of the void. Therefore al-Rāzī’s view of nature is well defined and opposed to the view of Avicenna and the Aristotelian philosophers, as we will see.
Despite their differences, the authors of kalām were united in articulating philosophy in accordance with the Qurʾānic teachings. They all agree on the temporal creation of the world and on the best-known proofs in favor of it relying on the connection of substances (atoms) and accidents. They both cannot exist independently.
Philosophy of Nature in the Falsafa
Basra lost its importance in the kalām tradition in favor of Baghdad, the capital of the Abbasid empire. The Abbasid Caliphs not only encouraged the science of kalām, but they were also eager to acquire the wisdom that had once flourished in the countries that Islam had conquered. There were already translations of Greek sources into Syriac, the main Aramaic dialect spoken across Mesopotamia and Syria, which was the basis for translations into Arabic. However, much more numerous were the translations made from Greek into Arabic under the auspices of the Abbasid Caliphs or of high-ranking personalities of their courts. Although medicine and astronomy initiated the movement, philosophy had its share in the translation movement too, and translation was the first step toward creating an Arabic philosophy.
Abū Yūsuf Yaʿqūb ibn Isḥāq al-Kindī (d. 870) is paradigmatic for this synthesis of translation and creation of philosophy. He arranged the translation of Aristotle’s Meta-physics, and the Theology falsely ascribed to Aristotle (Enneads IV–VI), and on the basis of the translations as well on the contributions of the Muʿtazilite kalām, he worked out his own philosophy.
His ideas on nature and the universe were conditioned by his Islamic belief that God created the world, which cannot be eternal. God is the only eternal, and the Eternal is mainly defined in negative terms. For instance, He is not a body; He has neither genus nor species. On the contrary, the universe is finite: it has a temporal beginning and its body is limited. In his treatise On First Philosophy, al-Kindī produces four proofs for creation. The first proof establishes the finiteness of the body of the universe, and as a result, it establishes the finiteness of time, because time is a predicate of this body.
The second proof insists that any quantitative entity cannot be infinite in actuality and that time must have a beginning; body, motion, and time are never prior to one another; therefore, are all limited. The third proof argues that composition and combination build bodies, which is a Muʿtazilite doctrine.
Composition and combination are motions, and through motion there is time; now, “if time is finite in actuality, then necessarily, the being of a body is finite in actuality”. But no doubt, the fourth argument is the most important to al-Kindī. It proves that an infinite cannot be traversed, and if time were infinite, the actual time could never exist. He argues:
Before every temporal segment there is (another) segment, until we reach a temporal segment before which there is no segment, i.e., a segmented duration before which there is no segmented duration. It cannot be otherwise – if it were possible, and after every segment of time there was a segment, infinitely, then we would never reach a given time – for the duration from past infinity to this present time would be equal to the duration from this given time regressing in times to infinity.
As H.A. Davidson has shown, al-Kindī employed some of Philoponus’ proofs for the temporal beginning of the universe. The temporal beginning implies that time is concomitant with body and motion; all the three come to be with the creation of the heavens.
In sum, the universe is finite in extension and duration. No void or plenum lies outside the universe. Its shape is spherical, and al-Kindī composed an essay entitled That the Elements and the Outermost Body Are Spherical in Form to sustain it. Al-Kindī has another treatise On the explanation that the Nature of the Celestial Sphere is different from the Natures of the Four Elements, which begins saying that physics, that is, the science of the natural beings, deals with the movable things because “nature is something that God made a direct cause (ʿilla) and a cause (sabab) for a direct cause of all that is capable of motion and of rest after motion”.
In these writings we read that there are four elements: earth, water, air, and fire; they are concentrically ordered according to their lightness or heaviness; the fire is the lightest, and the earth the heaviest. The outermost sphere extends from the perigee of the moon to the limits of the universe, and it is made of a fifth element, following Aristotle’s teachings, which is neither heavy nor light. In spite of their spherical form, the elements and the outermost body are very different. The elements consist of opposite qualities, something that is proved by their movements.
Al-Kindī distinguishes two kinds of motion, circular and rectilinear motion. The movements of the elements are rectilinear, and they are not continuous. In contrast, the celestial sphere moves always around the center “for the duration of its existence.” Al- Kindī concludes that this body cannot be made of any of the elements: its substance is simple.
As for the shape of the elements, al-Kindī shows familiarity with Plato’s doctrine of the polyhedra in the Timaeus. Plato assigned the tetrahedron to fire, the hexahedron or cube to the earth, the octahedron to the air, and the icosahedron to the water (54d – 55a); the dodecahedron, whose faces are not triangular, would represent the universe (55c). Al-Kindī follows him, but he combines his reading with neo- Pythagorean numerology. His interest in a geometrical explanation of the simple bodies is shared by the kalām in its explanation of the atoms.
Al-Kindī believes in the influence of the heavenly bodies upon the sublunary world and talks about the role of the Sun and the Moon as the efficient causes of generation and corruption; they carry out God’s providence acting upon the realm of generation and corruption. Moreover, the heavenly bodies are intelligent beings who serve God through their regular motions. Al-Kindī praises God for His providential design of the universe:
How perfectly has the Creator, great be His praise, arranged things by putting the sun close to the zenith above our heads, coming is high in the air and draws far away from the surface of the earth, so that it has reached the beginning of the declination (mayl); then it draws nearer to us until it arrives at the end of the declination.
Then it turns celestial equator descending and breaking the distance in the degrees whose declination in one direction is one. There are two different seasons in each inclination, and the seasons are four, corresponding in quality to the four elements.
Thus al-Kindī knew the Ptolemaic astronomy but also its astrology that associated spring with the element air, summer with the fire, autumn with the earth, and winter with the water. However the Islamic faith guides him to view God as the remote mind governing the universe. Al-Kindī offers us a general description of the physical world in which he agrees with the Muʿtazilite kalām on essential issues.
Abū Naṣr Muḥammad al-Fārābī (d. 339/950) offers us a more precise description, and he distances himself from kalām. In Baghdad, he met scholars, many of them Christians, who were engaged in the transmission of the Aristotelian corpus; and he mastered logic. Al-Fārābī constructed a system in which he tried to comprehend all the fields of philosophical speculation. Among his works, On the Perfect State and The Political Regime represent the most developed stage of his thought. Al-Fārābī decided there in favor of a generative model.
His system starts with the absolute One: “The First is that from which everything which exists comes into existence”. Everything comes into existence in a way like an overflow, fayḍ, which is commonly translated as emanation; it follows an exact order. The first emanated, that is, “the Second,” is an incorporeal substance, which is intelligence, a separate intellect. It is thinking itself and also is thinking the First. We may add, just as an aside, that knowledge of the cause and of the self is a crucial concept for Proclus and many Neoplatonists, as Damien Janos rightly reminds. From the Second thinking the First emanates the Third; from thinking itself, it becomes substance; and substance is here the First Heaven, the Outermost Sphere.
The process of “thinking itself and thinking the First” goes on through the spheres of the Fixed Stars, Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon; they are nine altogether. In each step we have a reciprocal process of being intelligent and being intelligible, i.e., they are Active Intellects, ʿuqūl, and passive intelligibles, maʿqūlāt.
The matching spheres are not composed of matter, although they are bodies; the spheres and their contents are composed of two principles of soul (nafs) and substrate (mawḍūʿ). Their motion is essentially harmonious and natural; they all move in circles but at different speeds so that they are affected by contrarieties of accidental import. The celestial bodies emit light, which is in turn responsible for generating heat in the sublunary world.
Al-Fārābī combined the metaphysics of Plotinus (d. 270 CE) and his school with the astronomy of Ptolemy (d. 161 CE), although he simplified it. Walzer thought that al-Fārābī was inspired by a later Greek tradition in his synthesis, but he could not identify any source. M. Maróth traces al-Fārābī’s equation between the intellects and the celestial sphere bodies to Alexander of Aphrodisias. The blending was very successful in spite of its intrinsic weakness, as it remains purely speculative.
Al-Fārābī assumes, for instance, an eternal creation of the universe, but he does not buttress the statement with arguments. According to al-Fārābī, after the Moon thinks the First, an Eleventh intellect comes into existence, but the process stops herewith. The last separate intellect is the Active Intellect, whose intellection is threefold, as it understands the First, the nine emanated intellects, and itself. The Active Intellect is necessary for the existence of the material beings as well as for intellectual knowledge by man.
Al-Fārābī emphasizes that the individuals existing under the sphere of the Moon have their most imperfect way of existence in the beginning, in contrast to the celestial bodies, which are always perfect. Matter has the most defective existence, and in ascending order of perfection, he aligns:
The elements such as fire, air, water, earth and things belonging to their genus such as vapor and flame and other things; the minerals such as stones and what belongs to their genus; the plants; the animals which lack speech [and thought], and the animals which have speech [and thought].
Al-Fārābī does not seem to distinguish between the elements as principles and as real individuals; he even understands prime matter as their effective matter: “the matters of the elements have no matter”. Through mixture, ikhtilāṭ, all material beings arise. The first mixture is that which combines some of the elements, and mixtures go on, but there is a last level of mixture: “Man alone arises as a result of the last mixture”. Mixture brings out various potencies or powers, some active and some passive.
Al-Fārābī adds the celestial bodies to the causes acting in the processes. He obviously believes in astrology and maintains that stars sometimes help and sometimes oppose the sublunary agents with their works. Al-Fārābī’s exposition is suggestive and rather imprecise. He depicts a dynamic nature in which opposite entities, muḍaddāt, which are either inherent or external to the body and their powers, qūwāt, overcome each other destroying substances and creating new ones.
Al-Fārābī sketches some rules such as the contrary that destroys an element must come from the outside or, when the mixture is not very complex, like in stone or sand, the contraries that destroy a body of a complex mixture “come simultaneously from outside and inside its body”.
Living beings are of a very complex mixture, and al-Fārābī adds that they can be destroyed by “things contrary to them from their inside.” Powers go from more defective to more perfect. In the case of man, the first power to arise is the nutritive faculty, followed by the faculties of the various senses, by the faculty of imagination, with the rational faculty as the highest. Sensation, imagination, and reason are complemented by parallel appetitive faculties. The exposition is neither original nor precise, although al-Fārābī makes further distinctions. He distinguishes between one ruling faculty and auxiliary faculties within the nutritive faculty as well as the faculty of sense.
He views the heart as the ruling faculty of nutrition and sensation. The faculties of imagination and reason have no auxiliaries. Al-Fārābī places the faculty of imagination in the heart: the heart is the ruling organ and is followed by the brain, which “is ruled by the heart and rules over all the organs and limbs”. Although he does not know precisely where the rational faculty resides – Aristotle did not either – he states that the rational faculty consists of a material part, which is “a shape, hay’a, in matter prepared to receive the imprints of the intelligibles”.
In order to become intellect in actuality, the material intellect, that is, man, needs something else, which is always in actuality, namely, the Active Intellect. Thus, al-Fārābī links together the world of nature with the celestial architecture, and man is the linking band.
Such an intervention of the Active Intellect that gives sublunary beings their forms is not mentioned by al-Fārābī’s in his writings. He gives all celestial bodies the decisive role of creating prime matter and the contrary forms of the sublunary beings. Nevertheless matter, the elements, and nature have an inherent force to develop into higher forms of existence.
How well organized are al-Fārābī’s doctrines? M. Mahdi claimed that his cosmology was political and devoid of scientific value since its purpose was to be a guide for the inhabitants of the virtuous city. On the contrary, D. Janos argues that the doctrines are consistent, “grounded in the most up-to-date physical, meta- physical, and astronomical theories of his time”. However, he recognizes in other places that al-Fārābī’s doctrines are not always homogeneous or that, for instance, he does not devote much space in his extant works to celestial motion, which is a crucial issue in physics.
Al-Fārābī’s carelessness may hint at the fact that he was much more concerned by a metaphysical foundation of ethics and politics.
In the tenth century CE and matching the lifespan of Al-Fārābī (ca. 870–950), a society of learned men flourished in Basra. They remained anonymous on purpose, and their interest in philosophy and science was stirred by a way of life, where knowledge was “nourishment of the soul.” The Brethren of Purity, as they called themselves, have bequeathed us with 54 epistles comprising all the learning available at their time. The epistles often combine Platonic and Aristotelian doctrines, but sometimes they drink from other sources, for instance, Pythagorean. Whether the epistles can be considered as a disseminating work aiming at a general audience or one intending to reach scientific level remains a matter of discussion.
Epistles 16 through 21 deal with the natural sciences; they have been translated into English by Carmela Baffioni (2013). The doctrine of the human being as a microcosmos enjoyed broad dissemination in medieval Islam, and the Brethren of Purity reproduce the doctrine of both man as a microcosmos and the universe as a macroanthropos. In Epistle 16, c. 2, we read:
Know, o my brother, that by saying ‘world’ the wise men mean the heavens, the earths, and all the creatures of them, and they called it a ‘big man’ because they think that it is a simple body with all its spheres, the layers of its heavens and the elements of its basic compounds, and the things generated from them. They believe that it has a soul whose faculties pervade all parts of its body as the soul of an individual man pervades all his parts.
In the classical issue of the character of the creation of the world, the Brethren of Purity join ranks with those who sustain the world. In several places, for instance, in the Epistle 42, they insist in the doctrine that the world is temporally created: muḥdath. Generally speaking, the Epistles are close to the falāsifa tradition, but they are not concerned by scholarly rigor and even contain matters of magic, astrology, and superstition. While Al-Fārābī’s school was based in Baghdad and the Brethren of Purity were active mainly in Basrah, Avicenna will move through different places of present Iran and Uzbekistan.
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā (d. 1037 CE) was indebted to al-Fārābī; however, his philosophy is not only most original but also embraces all aspects of knowledge. The major work that we know is The Book of Healing, an encyclopedia which begins with logic, more precisely with the Introduction, which is a reformulation of the Porphyrian Isagoge. Avicenna describes the purpose of philosophy as “the knowledge of the realities of all the things insofar as man can know them”. These things can be dependent on human will or not, and the latter are the subject of theoretical philosophy. They divide into things that mix with movement and things that do not. God and the intellect are the only beings that do not mix with movement.
Movement means something like engagement with matter. Avicenna tells us that the different sciences arise according to the relationship of beings toward movement. Some beings exist in movement in their intellectual apprehension, taṣawwur, as well as in their subsistence, qiwām; they cannot be separated from matter. Some beings exist in movement only in their intellectual apprehension; they can be separated from matter. Some beings exist in movement and can be separated from matter in their intellectual apprehension and in their subsistence. Natural science deals with the first kind of beings, mathematics with the second, and metaphysics, the “divine science,” with the third.
The Book of Healing contains a first section on logic considered as a preparatory part of philosophy, followed by a section on mathematics, and then a section on natural beings. The order may vary; in the Dānesh Nāmeh, the rank is Logic, Metaphysics, Physics, and Mathematics.
Following the rules of scientific knowledge exposed in logic, Avicenna enquires for the subject matter of physics. The subject matter of natural science is “the sensible body insofar as it undergoes change”, and he proceeds to describe the natural body:
The natural body is that substance in which you can presuppose an extension, then another extension cutting it vertically, and then a third extension cutting them both vertically. Its being, kawnu-hu, is the form by which it became a body.
The three-dimensionality is reminiscent of the kalām tradition, but it is not exclusive of it. Avicenna and the Muʿtazilite scholar ʿAbd al-Jabbār al-Asādabādī (d. 1025) might have met in Rayy, in 1013–1015, and textual evidence of a discussion on physical theory exists. For Avicenna, the three dimensions however are properties and not principles of the natural body because they are changing, not stable. He explicitly denies the existence of atoms and the void.
There are two principles that produce corporeity, matter and form, and a third one, privation, that intervenes in change and motion. Avicenna introduces a corporeal form, ṣūra jismīya, from which matter is never separable. When wax is squeezed and creased, it takes on many shapes while remaining a body. And matter and motion are the subject of physics.
As for the attribute “natural,” ṭabīʿī of the body, Avicenna affirms that “natural” comes from the relationship to “the potency, qūwa, called nature, ṭabīʿa”, but on the other side, he defines nature as “the efficient principle common to natural things”.
Nature in its restricted sense is the source of motion and change under two conditions “the action has only one outcome and is without volition”, and the example he gives is that of the stone falling and coming to rest at the center.
However Avicenna admits there are three other meanings of nature insofar as it is the source of motion with only one outcome but with volition, that of motion with variable outcome and no volition, and that of motion with variable outcome and volition. The rotation of the Sun belongs to the second category, and its proper source is the celestial soul; the generation, growing, and halting of the plants belong to the third category, and the proper source is the vegetative soul; the motion in place of the animals belongs to the fourth category, and its source is the animal soul. After this explanation, Avicenna considers that he has given enough reasons to call nature an efficient principle, and not an efficient cause, producing motion and to call it an efficient power too.
In The Book of Science, Avicenna observes that motion in a proper sense applies only to change in place but that it has acquired a broader sense, “any state and any actuality of something insofar as this something is in potency”.
Motion means change in general, which is found also in the categories of substance, quantity, and quality. Avicenna defines movement in the Book of Healing in similar terms, but he additionally distinguishes two meanings, internal and external, of movement. Its internal meaning is our perception of it as continuous; its external meaning is its existence as an intermediate state in the instant.
There is another division depending on that change, which takes place gradually, as colors sometimes do or, at once, as substances do. Substantial change occurs at once, motion in quantity as well as in place is always gradual, while qualitative change has both forms. In the case of sperm, which becomes an animal, the gradual progression is only apparent.
The distinction is not Aristotelian; Avicenna remarks that the Ancients, that is, Aristotle and the Greeks, referred to movement as only that which occurs gradually. McGinnis hints at the possible influence of John Philoponus concerning the affirmation that substantial change occurs at once, but here again we should not lose sight of the kalām tradition, including their doctrine of states. “Every body has a nature, form, matter and
accidents”; with this statement, Avicenna summarizes his views that differ from Aristotle; he integrates nature as a dynamical dimension into the composition of matter and form and adds the accidents as a necessary expression of any substance.
Since the realm of physics comprises simple and composite bodies, the simple ones are primarily natural. Simple bodies divide into those having only one potency or power and those having two potencies, for instance, one proceeding from the form and the other from an accident. Composite bodies receive the potencies corresponding to the bodies from which they are mixed, and if they blend, a common potency arises, which is mixed.
In his book On the Heavens and the World, Avicenna looks at the simple bodies and sees that they have simple movements, either circular or rectilinear. Bodies with circular movement are completely different from those moving in a straight line, that is, the elements. They are neither hot nor cold, neither heavy nor light. The simple spherical form has no contrary; it is not generated from anything simple, and it is created, mubdaʿ. As for the spherical matter, it does not have any contrary form; it is unalienable, mawqūf. He concludes that such a substance must be a soul endowed with the choice of movement.
The celestial body contains a number of stars, following a hierarchy since “we see that some eclipse others and that some cause a change of appearance, manẓar, and others do not.” Further, we observe that some stars move according to their approved movement, while others disobey and move in the opposite direction.
Avicenna comes closer to the results of observation; the Moon is dark and receives the light from the Sun, for instance. Some people claim that the earth is moving in a circle and the sphere is resting and that sunrise and sunset are not true. Avicenna refutes this because he proved that there is a resting body on which all others turn and which cannot be anything but the earth. He adds “if it were as they claim, a clod of earth would not fall vertical, but slanted, and the arrow thrown toward the east would reach a shorter distance than the one thrown toward the west”.
Avicenna’s universe is finite in extension and infinite in duration. He follows al-Fārābī’s design of the universe based on emanation; from the First Principle emanates an intellect one in number, it is the first of the separate intellects. Each sphere possesses a separate intellect “whose relation to it is as the relation of the Active Intellect to us”. The intellect cannot move directly but by means of the soul that is “the proximate principle of motion.” Each sphere is moved by the corresponding soul and each sphere has a body. Chapter four of Book IX of the “Divine Matters,” Ilāhīyāt, reviews the hierarchical structure (tartīb) emanating from the First Principle:
You know that we have here numerous separated intellects and souls. It is thus impossible that their existence should be acquired through the mediation of that which has no separate existence [from matter]. But you [also] know that the aggregate of existents proceeding from the First includes bodies […] these bodies come into being from Him through an intermediary.
The intermediary must have duality or plurality in itself so that it can produce the duality inherent to any body because a body is a possible existent by itself and necessary existent because of another. To sum up, the intellects and the souls can proceed directly from the First, but the bodies, and their possible matter, can only proceed through an intermediary that is contingent.
Moreover, it should be reminded that for Avicenna the number of unmoved movers or separate intellects is explained through the art of astronomy and therefore through observation. Because of the souls and the spheres, there is motion and herewith time comes to being; it depends on motion. More precisely, it is dependent on a single motion, and Avicenna even affirms that the body endowed with this single motion is the efficient cause of time.
Avicenna clearly means the infinite movement of the universe and adheres to Aristotle: “The head of the Peripatetic school has proved that the mover of the universal sphere moves it with an infinite motion, that his power is infinite and that this mover is not in any corporeal power”.
Composite bodies are investigated in the rest of the natural books including the treatises on animals. Living beings have the four kinds of motion; qualitative and quantitative motion is found in growth, for instance. The movers in the living body are its faculties or powers. The human faculties divide into natural, animal, and mental, and the heart is the principal organ that spreads the potentialities over all other parts; thus, the brain runs the mental faculty.
Avicenna designed a system, which extended from matter and from the simplest elements to biology and medicine. Avicenna started a new approach in the philosophy of nature when he used movement as the criterion to classify beings and then proceeded to study them. In addition, he tried to integrate observation within the system, but he eventually yielded to the seductive, all embracing emanation system designed by al-Fārābī.
His approach was successful throughout centuries of Islamic thought in the East, that is, Iran, regardless of the different developments of this thought. So we see the Qurʾānic commentator ʿAbd Allāh al-Baydawī (d. 1316?) and his disciple Maḥmūd Isfahānī (d. 1348) making a comprehensive effort to combine Avicenna’s philosophy and kalām. Al-Baydawī expounds on both doctrines about bodies. For instance, the mutakallimūn say that a body is composed of atoms, and the philosophers say that a body is continuous in itself.
Abū Bakr Muḥammad Ibn al-Ṣā’iġ Ibn Bājja (d. 1139), known in the West as Avempace, contributed to the development of the philosophy of nature. Ibn Bājja sketched a theory of dynamics based on a notion of “power” (qūwa) different from the Aristotelian notion of dynamis: his “powers” are mechanical forces, which can join with another force or counteract it by offering resistance. Shlomo Pines introduced the term “dynamics” to define his views, which were influenced by the tradition linked to John Philoponus.
There is a minimum amount of moving power for each movable. For instance, to move a boat, a minimum of manpower is needed. When two opposing powers are equal, there is no motion, and when one power “overcomes” the other, the body moves until it suffers “exhaustion,” kalāl.
Avempace made a remarkable contribution related to motion in the void; we are dealing here with “natural” movements such as a stone falling through air and water. Aristotle rejected the possibility of motion in the void because the medium was essential to natural movement at a finite speed. John Philoponus had already expressed the view that the medium is not a necessary condition but only provides resistance. The different velocity with which the stone passes through the air or the water is only caused by the different density of the medium; it is not connatural to the medium. As a proof that motion without any medium, namely, through a void, is possible, Avempace adduces the movement of the spheres:
[In the heavens] there are no elements of violent motion because nothing bends their movement; the place of the sphere remains the same and no new place is taken by it. Therefore circular movement should be instantaneous, but we observe that some spheres move slowly – such as the sphere of fixed stars – and others fast – the daily movement – and that there is neither violence nor resistance among them. The cause for the different velocities is the difference in nobility (sharf) between mover and movable.D. Wirmer has written a monograph on the role of potency/power in Avempace’s philosophy in which he extends the outreach of this concept from psychology to metaphysics through natural science and considers “active and passive potencies as universal explanatory principles” in Avempace’s thought.
No doubt, potency/power is not limited to the mechanical field, and it has a wider function in his natural philosophy. In the processes of a substance as well as in qualitative and quantitative changes, potency is an active and passive factor. Hot and cold are active potencies in the case of the elements, and as far as the passive potencies are concerned, Avempace explains them in the case of the element water:
Since the element insofar as element possesses a receptive potency of one of the composing forms, the water is neither [element] of the air nor of the earth nor of the fire, but it is element of the wine, of the vinegar, of the blood or of the phlegm, or of what belongs to the kind.
Avempace adds that the passive, or receptive, potency of each element divides into two. One underlies its transformation into other simple elements; the other allows it to receive the form of composite substances. He puts the oxymel as an example where the active and passive potencies intervene: the form arises by means of the active potency and the subsisting matter by means of the passive one.
Avempace makes a wide use of the concept of potency in natural philosophy, and the comparison with Avicenna and his use of “nature” comes to mind. Avempace shares with Avicenna his cosmological doctrines although he makes some interpretations of his own, when he calls “spiritual forms” the forms of the celestial bodies.
The correction in the sense of separating the account of timeless emanation from philosophical explanation came from Abū l-Walīd ibn Rushd,
Averroes (d. 1198). He reacted to the criticism of Abū Ḥāmid al-Ġazālī, Algazel (d. 1111) against Avicenna and resorted to Aristotle who did not know emanation as his source and guidance:
The habit of our contemporaries to say that such- and- such a mover proceeds from such- and- such a mover or emanates from it, or follows necessarily, or similar expressions, is something which is not correct in the case of these separate principles [the heavenly bodies].
Like Aristotle, Averroes admits the existence of these separate principles and adds that their number has to be established by the astronomer. He was not satisfied with Ptolemaic astronomy, but he could not propose another more Aristotelian version in this case. Since Aristotle’s works are not systematic, his disciple had to solve some inconsistencies, at least apparent.
When Averroes comments on Met. 1069a 30–32, his passage establishing three kinds of substances (i.e., a sensible one “of which there is one eternal and one corruptible” and another immobile) states that the sensible substance without generation and corruption is “the fifth body,” that is, the heavenly spheres, and insists that natural philosophy studies the principles of both substances. Physics and metaphysics complement each other. The metaphysician acquires from the philosopher of nature the assessment that the corruptible sensible bodies are composed of matter and form and that the eternal sensible body has an immaterial mover. In the beginning of his Epitome of the Metaphysics, he stresses the continuity of physics and metaphysics:
In sum, the first purpose of Aristotle in this science [metaphysics] is to expound on the part needed for knowledge of the remote causes of the sensible beings, because what he expounded in the natural science was only two remote causes, i.e., the material and the moving cause.
For Averroes, the books of Aristotle’s Physics consistently expound matter, motion, and related subjects as time and place; the treatises on Coming-to-Be and Passing Away and on Meteora deal with kinds of motion that are not in space, that is, substantial change and quantitative and qualitative change. Aristotle’s well-known definition of motion in Phys. 201a 10–11 reads: “motion is the perfection of that which is in potentiality under the aspect that it is in potentiality,” and Averroes comments on it that the movable has two kinds of perfection, a perfection in actuality and a perfection in potentiality, under the aspect of which it is called motion.
Averroes could have learned the distinction either from Philoponus or Themistius. He observes that the definition is valid for both eternal and non-eternal classes of motion, and he considers that the continuity inherent to motion shows in the definition itself. Averroes raises the question whether motion is a category in itself or it belongs to the category, i.e., the genus of the perfection toward which it intends, so that motion in substance belongs to the genus of substance and motions in quantity, place, and quality to the respective genera.
Averroes accepts both answers: insofar as transition toward a perfection is different from the perfection itself, motion is something different from its goal and considered in this way, “Motion must be a genus per se, for the way toward something is different from it [the end]”. For this reason, he believes Aristotle classified motion in own category in his book Categories.
Averroes sustains that motion does not differ from its final perfection essentially but only in a matter of degree, nisi secundum magis et minus. Therefore, the definition of motion as belonging to the genus of its perfection is more adequate, verior, although the definition of motion as a genus in itself is better known, famosior; Averroes points out that Aristotle in the Physics deals accordingly with the first definition. Medieval Latin philosophy would call this view of motion as genus in itself “a flow of form,” fluxus formae, and the contrary view, “a flowing form” forma fluens.
The issue of motion in the void was discussed by Avempace as we saw above; Averroes opposed to his solution, and herewith he made Avempace’s position known to the Latin philosophers. Averroes blames Avempace for misunderstanding the essence of velocity. Velocity is not a motion added to or subtracted from another motion, in this case, natural motion, “like a line added or subtracted from a line”. For Averroes, there is a ratio between the power of mover and the resistance of the movable, and a ratio between the hindering and the hindered, and velocity depends on both factors. Velocity in the celestial spheres results from the first kind of ratio, since there is no medium, and Averroes agrees with Avempace in considering the degree of nobleness (sharf) of the various spheres as the factor explaining their different velocities. Sharf is the surplus of “energy” between the power of motor and the resistance opposed by the movable.
Matter is another subject of inquiry in the Physics, as one of the four causes and as a principle. According to Aristotle (Phys. I.7–9), and Averroes, there are three principles: matter, form, and privation. In his commentary on the Aristotelian passage, Averroes points to the privation of form as the nature of matter. Prime matter is “almost composed of being and not-being”. Because of the presence of not-being in material beings, coming-to-be and passing-away is possible in them but not in heavenly bodies which do not have matter.
Sensible substances are made of matter and form, but both are of different kinds in celestial and corruptible bodies; the difference clearly appears – Averroes thinks – in the case of the corporeal form. Avicenna spoke of the corporeal form as that primary form, which gives a body its three dimensions and which is essentially prior to them. Averroes accepts the principle of corporeal form: matter never separates itself from the three dimensions, but he distinguishes between determinate and indeterminate dimensions. He blames Avicenna for missing this distinction.
Prime matter first receives the indeterminate three dimensions, which are identical with the corporeal form; the composite receives the determinate dimensions. This is not the case with the celestial bodies, whose forms do not exist by means of the three indeterminate dimensions. “They are not powers in bodies”. They cannot be powers in bodies, because celestial bodies have an infinite activity in spite of being of finite extension.
However, they have dimensions, and Averroes resolves the issue stating that celestial bodies receive the dimensions in a different way: “their matter receives the dimensions by means of its forms”, and the dimensions are obviously determinate.
Following Aristotle, Averroes describes the universe as a unique self-containing body in a spherical shape. It is neither heavy nor light; it is eternal and not corruptible; its only change is moving from place to place. While Aristotle introduces a fifth nature for the heavenly bodies, he cautiously explains that Aristotle meant that such a nature does not accept any changes.
In his commentaries on the Physics, Averroes deals with a discussion about the place of the celestial sphere, an issue raised by Aristotle in the Phys. IV.5 and one which concerned his Greek, Arab, and Latin commentators. Averroes first accepted Avempace’s explanation that the sphere is in a place by means of its concavity, so that its place is the convexity of the resting body that the sphere surrounds.
Later he rejected the distinction “from inside – from outside” and decided in favor of the distinction “essential – accidental” after discussing the views of Alexander of Aphrodisias, Themistius, al-Fārābī, and Avempace. The earth is at rest and has to be in a place per se; the heavenly body is rotating on it and can be in a place per accidens.
He is aware that some commentators regard Book VII of the Physics as superfluous because it proves what is better described in Book VIII – perfectius “as some commentators thought.” He does not agree that Book VII sets up a key premise for the enquiry: “everything that moves has a mover”.
The issue is neither that the hand moves the stick and the stick moves the stone nor that something moves because of a part of its whole; rather, it only moves accidentally. He gives as an instance of the latter the heart, which is the first movable in animals and is moved by some part that moves itself and the whole. The mover is not external but is found in the movable itself. According to Averroes, the inquiry excludes the corruptible bodies and leads to the one and simple movable, that is, the celestial body, and he concludes:
The following has now been proved: there is a first movable and a first movement. For this reason [Aristotle] presupposes at the beginning of Book VIII that there is a first movement and a first movable and investigates whether that movement is temporally produced or eternal.
Book VIII proves the eternity of the movement of the celestial body and also the immaterial nature of its mover. This is not the correct reading of Aristotle, who employed the definition of movement in general to prove its eternal duration, and, indeed, Averroes had followed the correct reading before changing his view.
In his revision of the epitome of the Physics, in his Quaestiones or even in the same text of the long commentary – although in form of a reconsideration of his previous opinion – he tells us that Aristotle’s aim at the beginning of Book VIII is to prove that the heavenly movement is eternal. Aristotle’s purpose here is not to demonstrate that motion does not pass away as genus (bi-l-jins) because he investigates a specific movement, that of the universe. Since he studies it as a whole, he does not consider its parts, where movements are following one after the other in an accidental succession. The cause of this eternal movement lies outside the universe and is not material. Physical inquiry leads to the existence of God as the Prime Mover.
The argument based on motion is seen as the best way for Averroes, Maimonides, and Aquinas to prove the existence of God, and Averroes deserves the credit for setting up this important proof in an explicit way. While Avicenna wanted to build his own “Oriental” philosophy independently from the Aristotelian tradition to which the Arab philosophers of Baghdad adhered, and he was proud of his achievements, Averroes just wanted to be a faithful interpreter of Aristotle.
However the history of ideas has its own dynamics, and volens nolens, Averroes essentially contributed to it.
Source: Encyclopedia of Medieval Philosophy, editor: Henrik Lagerlund, second edition pp. 1283 – 1302, Springer, 2020.
