GENERAL PRESENTATION OF IBN SĪNĀ'S COSMOLOGY

Ibn Sīnā's cosmology is directly indebted to Ptolemy's (d. c. 168 CE) model of the universe, which he knew from a direct study of the Arabic translations of Almagest and possibly Planetary Hypotheses.Footnote ³ This Ptolemaic model, however, had also been adopted by previous and contemporary Arabic astronomers, such as al-Farghānī (fl. 861 CE), Thābit ibn Qurra (d. 901 CE), and al-Battānī (d. 929 CE) who contributed to its diffusion and naturalization in high Islamic culture.Footnote ⁴ This model posits a spherical, immobile earth at the center of a finite universe, around which the various celestial bodies – orbs, stars, and planets – revolve in a continuous and regular fashion. It consists of nine main celestial orbs, arranged concentrically and nested in one another in an ascending order as follows: the orb of the moon, then that of Mercury, Venus, the sun, Mars, Jupiter, Saturn, and the fixed stars.Footnote ⁵ With regard to the latter, Ibn Sīnā is unsure whether all the stars are contained by only one orb or distributed among different orbs, although he usually refers to the orb of the fixed stars, perhaps for the sake of simplicity.Footnote ⁶ To this basic arrangement, Ibn Sīnā adds a starless and planetless orb, which he calls the “outermost body” (al-jirm al-aqṣā) and the “outermost orb” (al-falak al-aqṣā), and whose discovery he ascribes to Ptolemy.Footnote ⁷ This outermost orb encompasses all the other orbs and marks the outer physical limit of the cosmos. Beyond it there is neither matter nor void, for Ibn Sīnā follows Aristotle directly on this point.Footnote ⁸

Ibn Sīnā himself wrote a commentary on Almagest entitled Taḥrīr al-Majisṭī, which is still extant, and which shows that he was directly acquainted not only with the basic picture, but also the specifics, of Ptolemy's main work on mathematical astronomy, including the devices of eccentrics and epicycles, which Ptolemy had used to explain the various irregular motions of the planets.Footnote ⁹ Just as important as these Ptolemaic texts in shaping Ibn Sīnā's cosmological views, however, were al-Fārābī's treatises Principles of Beings and Principles of the Views of the Inhabitants of the Virtuous City. These works provided Ibn Sīnā with a model for how to integrate Ptolemaic astronomy in an otherwise Aristotelian and Neoplatonic framework and reconcile astronomical theories with physical and metaphysical ones. Although this endeavour had been inaugurated in Islam by al-Kindī (d. c. 873 CE) some time before al-Fārābī, it was the latter's theories that had the greater impact on Ibn Sīnā, judging from the many structural and conceptual parallels in their works.Footnote ¹⁰ These two thinkers devoted much space to cosmological questions in their philosophical treatises and – following the example that Aristotle had set several centuries earlier – they shared the common intention of reconciling the astronomical knowledge of their time with their physical and metaphysical doctrines.

This last statement nevertheless calls for elucidation, for unlike the later Arabic astronomical tradition, Ibn Sīnā and the early falāsifa do not systematically reconcile these disciplines in a single literary genre that can be compared to the hayʾa genre, embodied for instance in Naṣīr al-Dīn al-Ṭūsī's (d. 1274 CE) Tadhkira and in the works of Muʾayyad al-Dīn al-ʿUrḍī (d. 1266 CE). Rather, the falāsifa's adherence to the Aristotelian methodology and classification of the sciences leads them to discuss the various aspects of the celestial bodies in different treatises: the planets' motions are explained and represented mathematically in their commentary on Almagest, while the planets qua bodies and caused existents are discussed in the physics and metaphysics sections of their works. This being said, the falāsifa's cosmological approach is not disarticulated for that matter. They were definitely aware of the interrelatedness of these various disciplines and took into account the data of astronomy when writing about physics and metaphysics and vice versa. In the case of metaphysics, this is evidenced at a basic level by the assimilation of much astronomical material in Ibn Sīnā's metaphysical discussions. Mabdaʾ, Ilāhiyyāt of Shifāʾ, and Ishārāt, for instance, implicitly adopt the general structure of the Ptolemaic universe and its various orbs (including the devices of epicycles and eccentrics), which they treat as concrete, physical entities, and whose existence depends on higher causes. Ibn Sīnā mentions Ptolemy's Almagest and his own commentary on this work in the very midst of a discussion of celestial motion and the unmoved movers in the Metaphysics of Shifāʾ, thus illustrating the intertwinement of astronomy and metaphysics in the cosmology of the shaykh al-raʾīs.Footnote ¹¹ Moreover, Ibn Sīnā opens the Metaphysics of Shifāʾ with a strong statement on the value of astronomy for the metaphysical investigation: “the ultimate aim in this [metaphysical] science – namely, knowledge of God's governance, knowledge of the spiritual angels and their ranks, and knowledge of the order of the arrangement of the orbs – can only be arrived at through astronomy…”.Footnote ¹²

With regard to physics, Ibn Sīnā's Taḥrīr al-Majisṭī, in principle a work devoted exclusively to mathematical issues, opens with a discussion of certain problems whose solutions rely on physical assumptions, such as the existence of a fifth, special celestial element or substance in addition to the four sublunary elements, thus echoing Ptolemy's own use of physical principles in some parts of Almagest.Footnote ¹³ Moreover, in his treatise entitled Beginning of the Treatise Appended to the Summary of the Almagest Containing What is Not Indicated in the Almagest, Ibn Sīnā states that “it is incumbent upon us to bring that which is stated in the Almagest and what is understood from natural science into conformity,” a statement which will later be taken up by the hayʾa practitioners with utmost dedication, and which shows his cognizance of one of the fundamental problems undermining the Ptolemaic legacy.Footnote ¹⁴ This idea is reiterated by Ibn Sīnā himself in the Prologue of Shifāʾ, where he informs us that he wrote appendices to the Almagest in order to teach students how to “correlate astronomical observations with natural laws.”Footnote ¹⁵ This point is further developed in al-Samāʿ al-ṭabīʿī, a work in which Ibn Sīnā stresses the interrelatedness between physics and other sciences such as astronomy (ʿilm al-hayʾa) and the fact that the latter is based on physical and mathematical principles (mabādiʾ ṭabīʿiyya wa-handasiyya). He even refers to the Almagest in this connection.Footnote ¹⁶ Finally, one also finds an intermingling of physics and astronomy in the shorter astronomical treatise entitled al-Arṣād al-kulliyya, which appears in the mathematical section of Dānesh-nāmeh in Persian form and of Najāt in Arabic form. Although in principle a mathematical work, the first chapter opens with a description of the outermost orb as a “body” (jirm) and by positing its necessary influence on the motion of the physical orbs below it, a process which explains the universal westerly motion of the heavens.Footnote ¹⁷ It is noteworthy that in making astronomy to some extent dependent on physical principles, Ibn Sīnā is continuing a well-established late-antique trend, and one which had already been fully embraced by al-Fārābī some time before.Footnote ¹⁸

The foregoing shows that for Ibn Sīnā, astronomy, physics, and metaphysics are interrelated and mutually dependent sciences, and that they are meant to work together to provide a unified picture of the cosmos. This conclusion holds, even in spite of the fact that Ibn Sīnā, like al-Fārābī, subordinates astronomy and physics to the first, universal science of metaphysics, and that his cosmological analyses are distributed throughout his corpus according to a fixed disciplinary scheme: the mathematical study of the heavens appears in Taḥrīr al-Majisṭī; the physical examinations in Samā', al-Samāʿ al-ṭabīʿī, al-Nafs, and other minor treatises, such as al-Kawn wa-al-fasād and al-Afʿāl wa-al-infiʿālāt; and the metaphysical analyses (together with physical considerations) in his various metaphysical treatises, notably Ilāhiyyāt of Shifāʾ and Najāt. Yet among the wide variety of contexts in which cosmology is treated in Ibn Sīnā's corpus, it is in the metaphysical sections that one gets the clearest picture of how he conceived of the principles underlying planetary motion. This can be explained by the fact that the Metaphysics section of Shifāʾ defines the planets and orbs qua bodies and qua effects produced by higher causes, and is thus informed by a concern to explicate the status of the material heavens in the broader ontological scheme that characterizes Avicennan philosophy, while at the same time reconciling these metaphysical theories with astronomical material. Moreover, since the causes of celestial motion issue from physical and ultimately from metaphysical beings, they can only be explained satisfactorily by a science that deals with such existents and that can provide an explanation or proof of the reasoned fact behind this phenomenon, i.e., metaphysics, as opposed to astronomy, which does not deal with causation, and which therefore cannot properly identify the principles underlying celestial motion.Footnote ¹⁹ It is thus the metaphysical sections of Ibn Sīnā's works that come closest to providing a unified account of celestial motion and its causes. The following analysis will accordingly focus primarily on the metaphysical sections of his works, although references will be made to the other parts as well.

Keeping the foregoing remarks in mind, one may raise the important question of how Ibn Sīnā conceived of the existence of the orbs: are they purely geometric models or hypotheses that exist only mentally (mawjūdāt fī al-dhihn), or are they on the contrary concrete, individual entities possessing extramental existence (mawjūdāt fī al-aʿyān)? And if the latter, in what category or class of existents do they fall into? The evidence that can be gleaned from Ibn Sīnā's corpus overwhelmingly points to his belief in the concrete, extramental existence of various kinds of celestial bodies and orbs. Al-Fārābī had already defined the orbs (aflāk) as “spherical bodies” (sing. jism kurī) in Ārāʾ, and Ibn Sīnā follows his lead in this respect.Footnote ²⁰ In K. al-Ḥudūd, Ibn Sīnā defines falak as “a simple, spherical body [jirm basīṭ kurī] that does not accept generation and corruption and that is moved by nature [bi-al-ṭabʿ] around a center that it encompasses,”Footnote ²¹ while in the Metaphysics of Shifāʾ he refers to the form (ṣūra), matter (mādda), and dimensions (abʿād) of the orbs, thus emphasizing their hylomorphic composition.Footnote ²² Further evidence is found in The Ten Questions, where he explains that the planets (kawākib) are fixed (markūza) in the bodies of the spheres of their orbs (ajrām kurāt aflākihā), and he even mentions the epicycles explicitly (kurat tadwīrihā) in this context.Footnote ²³ Finally, in Ishārāt, Ibn Sīnā writes:

These passages, and especially the last two from Ten Questions and Ishārāt, indicate clearly that Ibn Sīnā considered not only the planets, but also the various kinds of moving devices – concentric and eccentric orbs and epicyclic spheres – to fall in the category of “spherical bodies” (ajsām kuriyya) and thus to be concrete, corporeal existents. This view on the physicality of the orbs is echoed in virtually all of Ibn Sīnā's philosophical treatises and is also predominant in the post-Avicennan tradition.Footnote ²⁵ On the basis of other passages, it is possible to add that Ibn Sīnā regards these orbs, as well as the other celestial bodies such as the stars and planets, as being devoid of the elemental qualities associated with sublunary elements (such as lightness, heaviness, coldness, etc.) and as consisting of another element altogether, which, following Aristotle's De caelo and the Peripatetic tradition, he calls aether (athīr) and a fifth nature (ṭabīʿa khāmisa).Footnote ²⁶

The fact that Ibn Sīnā believes that not only the planets and stars, but all the orbs and spheres as well, are bodies, says much about the relation between astronomy and physics in his cosmology, for it places him squarely on one side of an issue that had generated much disagreement in antiquity and which would also provide fuel for the hayʾa tradition.Footnote ²⁷ The direct implication of Ibn Sīnā's position is that the various kinematic devices discussed in detail in his Taḥrīr al-Majisṭī are not merely abstract mathematical models, but rather models that correspond to the physical reality. This in turn implies that astronomy is not opposed to the physical facts, but rather fully complementary with the findings of physics. Moreover, it raises the problem of the number of physical entities in Ibn Sīnā's cosmos. One often reads in the modern literature on Ibn Sīnā's cosmology that it contains nine celestial orbs, which correspond to the seven planetary orbs, the orb of the fixed stars, and the outermost orb. While this picture is essentially correct, it is in fact a simplification of a much more complex reality. Indeed, and as the previous passages show, Ibn Sīnā's cosmology is composed of a higher number of orbs, for each main orb is itself composed of a bundle of different kinds of spherical bodies, eccentrics or deferents and epicycles, in addition to the planets. Hence, although one may speak of nine main planetary orbs or systems, such as the ‘main orb of the moon’ or the ‘main orb of Mars,’ it should be understood that these main orbs themselves contain a varying number of subordinate spherical bodies depending on the complexity of the planetary motions involved.Footnote ²⁸

Ibn Sīnā himself does not explicitly mention the total number of orbs he considers most likely to exist in the heavens, nor does he mention Ptolemy's opinion on the matter. These omissions render the reconstruction of his cosmology quite difficult. The problem is compounded by the discrepancy that exists between his commentary on Almagest, which follows the trend of mathematical astronomy by referring to the planetary devices as circles (sing. dāʾira), and the accounts found in his physical and metaphysical treatises, which describe physical orbs. Since the numbers of physical orbs and circles do not correspond to one another, Ibn Sīnā's mathematical models cannot be used as a guideline for inferring the number of physical orbs in his cosmology. This problem is illustrated by Ṭūsī's Tadhkira, for instance, which computes either 22 solid orbs or 32 circles on the basis of Almagest. But regardless of this discrepancy, some insight may be gained from Ṭūsī's work: he adduces an additional 45 solid orbs to account for all the planetary motions. Thus, while Ṭūsī comes up with a total number of 22 solid orbs when describing the Ptolemaic system, his own astronomical model, which he regards as an improvement on that of Ptolemy, requires 67 physical orbs.Footnote ²⁹

On the basis of Ṭūsī's observations, one may hypothesize that Ibn Sīnā may have come to a similar conclusion regarding the number of orbs in Ptolemy's astronomical scheme. While Ibn Sīnā probably ignored the subtleties of the planetary models later developed by Ṭūsī that posit 67 orbs, he on the other hand would have been aware – perhaps by reading Planetary Hypotheses directly – that at least 22 orbs are required for Ptolemy's cosmological system to be functional. This hypothesis is strengthened by Ṭūsī's commentary on Ibn Sīnā's Ishārāt, which in the course of a cosmological elucidation mentions 22 orbs, as well as by the fact that a lesser number would have barely sufficed to account for the plurality of planetary motions – a fact that Ibn Sīnā was well aware of, given his repeated assertions that the planetary motions are numerous and varied.Footnote ³⁰ But given the high number of orbs recommended by both Ṭūsī and ʿAbd al-Laṭīf al-Baghdādī in their own works (67 and 77 respectively), it is also possible that Ibn Sīnā opted for a higher number of orbs. And indeed, in his Refutation of Astrology, Ibn Sīnā states that there are close to sixty orbs and spheres in the heavens, including the epicycles, although he does not give any information on their organization.Footnote ³¹

At any rate, and leaving this question aside for the time being, we can be certain that Ibn Sīnā posited more than nine celestial orbs, since he describes the eccentrics and epicycles as bodies, and since the latter need to be contained by larger concentric orbs. The various kinds of celestial bodies in Ibn Sīnā's cosmology can thus be divided into the following categories: stars, planets, concentric and eccentric orbs, and epicyclic spheres. This explains why in some texts Ibn Sīnā contrasts the minor or particular orbs (aflāk and kurāt juzʾiyya) to the main orbs (aflāk and kurāt kulliyya), the former consisting of the eccentrics and epicycles that are contained by the larger concentric orbs.Footnote ³² For simplicity's sake, however, the minor or particular orbs are often left out in cosmological discussions. In fact, the trend of referring to a simplified cosmology that only mentions the main orbs and ignores the minor or subordinate orbs can be traced back to ancient Greek thinkers such as Alexander of Aphrodisias (fl. c. 205 CE), Adrastus of Aphrodisias (fl. second century CE), and Simplicius (d. c. 560 CE), and it was then transmitted to the Islamic world and perpetuated by early Arabic thinkers. But this point should not obscure the fact that for these Greek authors, as well as for Ibn Sīnā, the physical arrangement of the heavenly entities was much more complex than this simple cosmological picture would suggest.Footnote ³³

Ibn Sīnā considers all of the orbs and planets to be aetherial bodies that move “by nature” (bi-al-ṭabʿ) without constraint or compulsion and with a regular, harmonious, circular motion. One implication of this view is that the planets do not transpierce their orbs or spheres, that is to say, that the planets do not move freely within their orb or in an opposite direction as their orb, as a fish swimming against the current of a river for instance, for this would imply a forced or contrived movement, a notion that finds no place in the heavens. Rather, according to Ibn Sīnā, the planets and stars are “fixed” (markūza) on their orbs or spheres, which means that they move together with the motion of the orb or sphere that carries them along. This view is stressed in a number of works, but finds a clear formulation in Ishārāt when Ibn Sīnā states that “the planets [kawākib] move around the earth on account of the orbs [aflāk] in which they are fixed [markūza], and not by transpiercing the bodies of the orbs.”Footnote ³⁴ While he attributes this view to the “school of Aristotle,” Ibn Sīnā ascribes to Ptolemy the opposite theory according to which the planets pierce their surrounding orbs.Footnote ³⁵

All celestial bodies possess a circular motion, which is the most perfect and harmonious motion and the only one that befits their exalted status and noble nature. According to Ibn Sīnā, however, the heavens possess various different kinds of circular motions. There is to begin with the universal westward motion shared by all the orbs, which Ibn Sīnā calls the motion of the whole (ḥarakat al-kull), and which elapses in a day and a night and marks a complete revolution of the heaven on itself. As McGinnis showed in an article, Ibn Sīnā introduced a new category of “motion in position” (ḥaraka waḍʿiyya) in addition to the standard theory of motion in place (ḥaraka makāniyya) to account for the rotation of the entire heaven around its own center.Footnote ³⁶ There is nevertheless some ambiguity in Ibn Sīnā's works concerning the way in which this universal motion unfolds. On the one hand, it could be transmitted from the outermost orb to the inner orbs. Accordingly, the motion of the outermost body (ḥarakat al-jirm al-aqṣā), would be shared by all the inner orbs as well, since these are contained by it. This view nevertheless raises certain problems: Would this transmission be achieved mechanically through physical contact or through emanating powers?Footnote ³⁷ On the other hand, it is possible that Ibn Sīnā adopted another explanation that was already used by ancient Greek astronomers, and which consisted in ascribing additional concentric orbs to each planetary system to account for the diurnal motion of all the heavenly orbs.Footnote ³⁸ As Ibn Sīnā is laconic on this issue, it is unclear which model he adopted. Moreover, these purely astronomical considerations have to be interpreted in light of his theory according to which the celestial souls have a common object of contemplation in God, which causes the continuity and circularity of celestial motion, and which could also be used to account for the universal westward motion shared by the entire heaven.Footnote ³⁹

In addition to this universal, westward motion, ancient and medieval observers perceived various eastward motions proper to the stars and planets. In the case of the orb of the fixed stars, this motion is the precession, which affects all the stars simultaneously, for these are fixed on the same orb and thus maintain the same distances to one another. While sharing this motion with the fixed stars, the planets also possess various individual easterly motions, which make them ‘wander’ or stray from the westward motion of the heavens, hence their Arabic name al-mutaḥayyira.Footnote ⁴⁰ These particular planetary motions are explained by means of the various minor spheres and orbs associated with each planet, i.e., the eccentrics, deferents, and epicycles, a subject treated in depth in Ibn Sīnā's Taḥrīr al-Majisṭī. Finally, Ibn Sīnā seems to have accepted the view that the planets and stars turn around their own center and thus possess their own individual motion in position, and this in spite of the fact that they are fixed on their epicycles.Footnote ⁴¹

Now that the basic structural features of Ibn Sīnā's cosmology have been discussed, I wish to turn to the key question of how he conceived of the causes of celestial motion. In broaching this subject, Ibn Sīnā engages in dialogue with a long Greek philosophical tradition that saw the movement of the stars and planets as a manifestation of higher ontological principles at work, namely, soul and intellect. In various parts of his corpus, but especially in the Ilāhiyyāt section of his philosophical summae, Ibn Sīnā methodically outlines the various physical and metaphysical principles responsible for moving the heavenly bodies. There are to begin with the celestial souls (al-anfus al-samāwiyya), which are the “proximate movers” (sing., al-muḥarrik al-qarīb) of the heavens.Footnote ⁴² Following Alexander in Mabādiʾ, Ibn Sīnā believes that these celestial souls are the forms (sing. ṣūra) and perfection (kamāl) of the celestial bodies.Footnote ⁴³ As a result, they are closely linked to the celestial body, to the extent that Ibn Sīnā describes these celestial souls as being “corporeal, transformable, and changeable, and […] not denuded from matter.”Footnote ⁴⁴ This statement should be interpreted in light of Ibn Sīnā's belief that these souls possess imagination (takhayyul) and estimation (wahm), faculties which constitute part of the inner senses (ḥawāss bāṭina) in his psychology and which are usually closely connected with sensual perception and therefore with the bodily organs. In the context of Ibn Sīnā's cosmology, these faculties have for chief function to enable the orbs to know particular things (juzʾiyyāt).Footnote ⁴⁵

In spite of their close relation to the celestial body, however, these celestial souls are also rational insofar as they have choice (ikhtiyār) and will (irāda), faculties which enable them to choose to contemplate the sublime intelligible nature of the higher substances (the separate intellects and the First Cause) and to engage in the continuous imitation (tashabbuh) of these higher existents. As Genequand pointed out, Ibn Sīnā's theory of celestial contemplation as a kind of imitation is indebted to Alexander's Mabādiʾ, but it more broadly perpetuates a late-antique cosmological trend.Footnote ⁴⁶ Accordingly, the celestial souls possess a desire (shawq) of an intellectual kind (and which is therefore identical to will or irāda) to attain and assimilate themselves to the “true good” (al-khayr al-ḥaqīqī) and to imitate the First (tashabbuh bi-al-awwal).Footnote ⁴⁷ Due to their corporeal nature, the celestial bodies nevertheless cannot attain the perfections of the higher principles. This metaphysical shortcoming translates into the circular motion of the orbs, which is the closest they can get to reproducing – albeit at a corporeal level – the perfections of the immaterial existents.

Ibn Sīnā's account of the celestial souls is thus multifaceted and closely modelled on human psychology: on the one hand, the heavenly souls have a rational faculty, but on the other hand they also possess imagination and estimation, which underscores their close relation to their material substrate, to the point that they are described as “corporeal” souls, or souls entangled with matter. The key role these celestial souls play in celestial motion both in contemplating the higher principles and in transmitting kinematic powers to the orbs is quite complex and will be examined at a further stage. For the time being, it is worth raising the question of whether these souls inhere in all the celestial bodies, including the planets, eccentrics, and epicycles, or whether the planets or orbs alone are ensouled. While Ibn Sīnā explicitly ascribes a soul to each planet and sphere in his Refutation of Astrology, he does not dwell much on this point in his main philosophical works. Yet it may be inferred from the passage of Ishārāt quoted above, as well as from Mabdaʾ, and, finally, from Ṭūsī's Sharḥ al-Ishārāt, that according to the shaykh al-raʾīs all the celestial bodies are ensouled.Footnote ⁴⁸

Second, and above the celestial souls in the ontological hierarchy, are the separate intellects (al-ʿuqūl al-mufāriqa). These intellects, whose number has traditionally been fixed at ten, are immaterial beings fully engaged in the act of beholding or contemplating the First and Necessary of Existence (wājib al-wujūd), from which their existence ultimately derives. As a result, and by virtue of their immaterial nature, they are in a constant and unchanging state of perfection.Footnote ⁴⁹ With regard to celestial kinematics, what is important is that the separate intellects act as final causes of motion for the orbs insofar as they are the object of the celestial souls' contemplation. Like al-Fārābī before him, who describes the separate intellects as “movers” (sing. muḥarrik) in Risāla fī al-ʿaql, Ibn Sīnā identifies the separate intellects as the “remote principles” (sing. al-mabdaʾ al-abʿad), the “motive principles” (sing. al-mabdaʾ al-muḥarrik), and the “separate movers” (al-muḥarrikāt al-mufāriqa) of the planets and orbs.Footnote ⁵⁰ Hence, according to this picture and to the traditional interpretation of Ibn Sīnā's cosmology, for each main orb there corresponds a separate intellect, namely, one intellect for the outermost orb, one for the orb of the fixed stars, one for the orb of Saturn, etc., with a total of nine main orbs and nine intellects, excluding the Agent Intellect, whose chief function is the governance of the sublunary world.

As for the First, which is also an intellect, it plays a role in celestial motion not by moving the outermost orb specifically – as in Aristotle's cosmology (Metaphysics XII.8.1072a), where the First Unmoved Mover is responsible for moving the orb of the fixed stars directly – but by being an object of thought and desire for the heavens as a whole. The First is a universal intelligible whose contemplation inspires a) the perpetuity and b) the circularity of the motion of all the orbs. It is thus the separate intellects, which, qua secondary objects of thought, inspire the particular motions of the orbs.Footnote ⁵¹ This explains why Ibn Sīnā also calls God the “First Mover” (al-muḥarrik al-awwal) and the “Mover of the Whole” (muḥarrik al-kull) in the context of his celestial kinematics. It inspires the constant, regular motion of the orbs by way of imitation (tashabbuh), and it acts as a final cause of motion for all the beings below it.Footnote ⁵²

It is noteworthy that Ibn Sīnā believes he is following a long philosophical tradition in positing multiple principles of motion and in distinguishing between proximate, inherent movers on the one hand (i.e., the celestial souls) and remote, separate movers on the other (i.e., the separate intellects). More specifically, he inscribes himself in what he regards as the Peripatetic school and refers to the authority not only of Aristotle, but also of Alexander and Themistius (d. c. 390 CE). According to Ibn Sīnā, all of these thinkers recognized one mover for the entire heavens, but at the same time they ascribed a separate, particular mover to each orb, and, finally, they also upheld the ensoulment of the orbs. These three tenets form the core of the Avicennan conception of the Peripatetic cosmological tradition.Footnote ⁵³

Finally, and in addition to the First, the separate intellects, and the celestial souls, it may be hypothesized that the orbs and spheres themselves play a causative role in the realization of celestial motion and represent an additional principle of motion, albeit one that operates at another level from that of the souls and intellects. This, however, is a vexed question, for Ibn Sīnā provides very little information on the kinematic causality of the orbs qua bodies. As bodies carrying the planets along, the eccentrics and epicycles may be seen as motive causes, in the same way that the hand moving an object is in part responsible for this object's motion. Moreover, according to De caelo I. 2-3 and to the Peripatetic tradition, aether has an inherent inclination for circular motion, which means that the orbs may be said to possess their own inner principle of circular motion qua aetherial bodies. While Ibn Sīnā recognizes the inherent propensity or inclination the celestial substance has for circular motion, he nevertheless minimizes this correlation in his philosophical treatises and never presents aether as a cause (sabab) moving the stars and planets.Footnote ⁵⁴ Rather, soul and intellect appear as the two main principles and causes underpinning celestial motion, while the circular inclination of the orbs merely represents the medium through which this causality operates. Hence, although it is tempting to ascribe some kind of kinematic causation to the orbs themselves, Ibn Sīnā's emphasis on the psychological nature of celestial motion seems to exclude this possibility or to greatly minimize it.

Now that the basic principles underlying celestial motion have been identified, I wish to examine this phenomenon in more detail, first, by addressing the central problem of the number and activity of the separate intellects in Ibn Sīnā's cosmology, and second, by examining the relation between the celestial souls and the celestial bodies.

THE PROBLEM OF THE NUMBER OF UNMOVED MOVERS AND THEIR RELATION TO THE CELESTIAL ORBS

The foregoing discussion leads to a problem that brings us to the heart of this article and that may be formulated as follows: If we adhere to the prevalent scholarly view according to which Ibn Sīnā follows al-Fārābī in positing ten separate intellects after the First Cause (or nine intellects if one excludes the Agent Intellect, which is not involved in celestial motion), then there would be a fundamental discrepancy in Ibn Sīnā's cosmology between the number of unmoved movers and the number of orbs and planetary motions. This, as we have seen, is due to the fact that Ibn Sīnā posits a high number of celestial bodies, for each main orb can be broken down into its constituent parts, i.e., the planet, the eccentric(s), and the epicycle, perhaps with a total of 22 orbs and spheres, if we retain Ṭūsī's assessment of Ptolemy's astronomical model, or with a greater number of planetary devices, if we assume that Ibn Sīnā added other orbs and spheres to this model and modified it considerably. Moreover, Ibn Sīnā clearly states that the planets are characterized by a plurality of motions, for they stray from the general westward motion of the outermost orb. How then are these nine unmoved movers able to account for such a wide range of planetary motions? Why is there no apparent correlation in Ibn Sīnā's system between the number of separate intellects and the number of planetary motions and orbs? If he was following the model outlined in Metaphysics, Book Lambda 8, then he would, like Aristotle, have posited as many movers as there are celestial motions. Themistius in his Paraphrase of Book Lambda, for instance, follows Aristotle in arguing that there are 47 or 55 orbs and then states that “it is necessary that the number of motions be equal to the number of orbs that move, and that the number of motive causes be equal to the number of motions.”Footnote ⁵⁵

The previous problem issues from the assumption that Ibn Sīnā followed al-Fārābī's theory of the ten intellects. Although this assumption has been widely accepted in the secondary literature, it is in my eyes questionable and will accordingly be addressed in the following paragraphs.Footnote ⁵⁶ The crux of the problem lies in Ibn Sīnā's understanding of how the separate intellects relate to the celestial bodies and of the role they play in causing the individual motions of the planets. He adopts an ambiguous position in this regard and even provides two contrasting explanations. The crucial passage that encapsulates this aporia appears in Metaphysics 9.2 of Shifāʾ when, after having settled the immateriality of the separate intellects by relying on the authority of the commentators, Ibn Sīnā then addresses the question of their number:

He begins by stating the following:

Having defended the need for separate intellects that would correspond to each orb, Ibn Sīnā then goes on to discuss whether a separate intellect should be ascribed only to the main celestial orbs or to each individual orb, including the subordinate or minor ones:

This passage, which also appears in an identical form in Najāt and in a modified form in Mabdaʾ, shows that Ibn Sīnā was aware of the existence of two different kinematic models and of two contrasting interpretations concerning the relation between the separate intellects and the motion of the celestial orbs.Footnote ⁶⁰ The ‘second kinematic model’ described by Ibn Sīnā is none other than Aristotle's cosmological model as it appears in Book Lambda 8, where “each moving orb has a rule [ḥukm] governing its own motion,” so we need not dwell on it much for the time being.Footnote ⁶¹ Suffice it to say that Ibn Sīnā studied Book Lambda 8 carefully – as he tells us himself in his Autobiography, he read the Metaphysics forty times – and he even wrote a commentary on it, part of which is still extant.Footnote ⁶²

It is the ‘first kinematic model’ which interests us here. In this alternative model, Ibn Sīnā explains that one can drastically reduce the number of separate intellects if one adopts a different interpretation of how celestial motion takes place. This interpretation, which dispenses with the high number of movers posited by the other model and relies instead on only ten movers, puts forth the theory of powers (quwan) emanating from the planets. In spite of the brevity of this passage, I believe that we should understand Ibn Sīnā as saying that these powers are transmitted by the souls of the planets to the corporeal components associated with these planets, such as the eccentrics and epicycles, and that it is this process that enables celestial motion to take place. What is significant here is the fact that this theory departs from Aristotle's Metaphysics Book Lambda, both in rejecting the high number of intellects it advocates and in introducing philosophical concepts foreign to it, such as the emanating planetary powers.

Other passages from Ibn Sīnā's works that discuss the ‘first kinematic model’ should be invoked here, for they can shed additional light on the problem and confirm the precedent interpretation. In Mabdāʾ, Ibn Sīnā explains that

And Ibn Sīnā continues:

This account presents various key points that parallel the ones outlined in the Metaphysics of Shifāʾ. First, it informs us that some thinkers locate the celestial souls in the planets alone – not in the orbs – thereby comparing the planet to the heart and the orbs and spheres to the limbs or muscles of an animal. Second, it ascribes emanating powers to the planetary souls in a way similar to the Shifāʾ passage, since motion can only be explained by the influence of the planets on their surrounding orbs, which are mere limbs that obey the planetary souls. It should be noted that the reverse is true for the orb of the fixed stars: in this case, the orb is the governing principle and directs the motion of the stars. Third, this model adjusts the number of celestial souls and separate intellects to the main orbs alone, i.e., to the seven planetary orbs, to the orb of the fixed stars, and presumably to the outermost orb (which is nevertheless not mentioned in this passage) and does not take into account the minor orbs (kurāt juzʾiyya), i.e., the eccentrics and epicycles. By implication, this model posits only nine celestial souls and separate intellects. Hence, the Metaphysics of Shifāʾ and Mabdāʾ provide us with two different descriptions of what is essentially the same kinematic model.Footnote ⁶⁵

The first step is to identify the sources and antecedents of this model. One hint, and a possible starting point, is the notion of emanating planetary powers. The concept of power (quwwa, or δύναμις in Greek) is frequently found in a cosmological context from Plato and Aristotle to the late-antique commentators of the sixth century, and it also appears frequently in the early Arabic philosophical texts. It thus covers a rich scope of meaning, which makes any comparison with Ibn Sīnā's work delicate. However, one important lead here lies in its connection with the planets specifically, which, I would argue, may be traced to Book Two of the Arabic version of Ptolemy's Planetary Hypotheses. In this work, Ptolemy explains that the planets possess a “psychological power” (quwwa nafsāniyya), which is responsible for bringing about their own motion as well as the motion of the orbs. The relevant excerpt belongs to a larger discussion in which Ptolemy seeks to explain planetary motion by establishing an analogy between the heavenly bodies and the sublunary existents, in this case birds:

Ptolemy then goes on to write:

In another passage, Ptolemy explains:

Ptolemy establishes an analogy between sublunary beings and the planets to illustrate how celestial motion occurs. While it is unclear how strictly one should construe this analogy, the main point made by Ptolemy is that the planet, and more specifically, the planet's psychological power, is responsible for moving the various corporeal parts associated with it, which include not only the planet itself but also the eccentrics and epicycles. As Murschel explains, for Ptolemy, “each planet … has the power to direct its own motions and the motions of the adjacent celestial bodies within its own system… The planet's psychic faculty sends motive emissions to the epicycle, then to the deferent, then to the outermost of that planet's celestial bodies, which is concentric with the earth.”Footnote ⁶⁹

The theory of celestial motion found in Ptolemy's work therefore corresponds in many remarkable ways to one of the two kinematic models discussed above and outlined in the Metaphysics of Shifāʾ. These accounts share an essential feature: they endow the planets with the capacity to send emissions (sing. inbiʿāth) or to emanate powers (quwan) to the other corporeal components surrounding them, such as the eccentrics and epicycles. They thus make the planets the chief agents of celestial motion by allowing them to dictate their own motion as well as that of the other celestial bodies within their system. Moreover, in Mabdaʾ and Najāt Ibn Sīnā uses the exact same expression quwwa nafsāniyya with regard to celestial motion, although in these cases he may be extending this concept to all the celestial bodies and not just to the planets. According to Ibn Sīnā, this psychological power is the “proximate principle for [celestial] motion” and is located in the celestial soul, also described as the “proximate mover” of celestial motion.Footnote ⁷⁰ These conceptual and terminological parallels are quite striking and suggest that Planetary Hypotheses represents one of the sources, if not the main source, behind the kinematic model described by Ibn Sīnā.Footnote ⁷¹

Surprisingly, however, Ibn Sīnā himself does not connect this kinematic model with Ptolemy. In Mabdaʾ, he ascribes the model of ten intellects and emanating planetary powers to “the moderns” (al-mutaʾakhkhirūn) and, in another instance, to “a group among the learned” (qawman min al-afāḍil).Footnote ⁷² Although no names are mentioned, it is likely that Ibn Sīnā has al-Fārābī in mind, since this thinker developed an easily recognizable ten-intellect cosmology, and perhaps also Ḥamīd al-Dīn al-Kirmānī (d. 1020 CE), who based his cosmological model closely on that of al-Fārābī.Footnote ⁷³ At any rate, Ibn Sīnā's remarks indicate that this kinematic model was upheld by some of his contemporaries, and we may also infer from Ṭūsī's Sharḥ al-Ishārāt and Ibn Rushd's Talkhīṣ fī mā baʿda al-ṭabīʿa, which also discuss it, that it was widely known in medieval Islamic times.Footnote ⁷⁴

Furthermore, it is important to note that while the ‘first kinematic model’ finds an important point of origin in Planetary Hypotheses, it also includes the theories of the unmoved movers and the intellection of the celestial souls, theories which are foreign to Ptolemy's works.Footnote ⁷⁵ This suggests that it may best be described as a synthesis of various kinematic, psychological, and metaphysical theories achieved by some (early Arabic?) thinkers, who relied not only on Ptolemy but also on Aristotelian and possibly Neoplatonic texts.

Returning to the alternative or ‘second kinematic model,’ which is described alongside this one, Ibn Sīnā in Shifāʾ provides little information on its various features apart from the fact that it posits a higher number of separate movers than the ‘first kinematic model,’ i.e., that it posits as many movers as there are orbs and motions. But in this case, there is no ambiguity concerning the lineage of this model, and Ibn Sīnā explicitly ascribes it to Aristotle (both in Shifāʾ and Mabdaʾ, which provides a slightly different and more extensive version and which will be discussed later on).

Having shed light on some of the sources underlying these two kinematic models, I now want to turn my attention to the question of which model Ibn Sīnā adopted in his works. It might seem obvious at first glance that Ibn Sīnā adopted the ‘first kinematic model.’ The rationale behind this argument is that since Ibn Sīnā adopted al-Fārābī's theory of ten separate intellects, he must consequently adhere to the first of the two kinematic models he outlines in this passage of Shifāʾ, since the other model posits a much greater number of separate intellects.

EVIDENCE FOR IBN SĪNĀ'S ADHERENCE TO THE ‘SECOND KINEMATIC MODEL’ OR THE ‘REVISED ARISTOTELIAN MODEL’

This assumption nevertheless runs into difficulty when one realizes that there is much evidence in Shifāʾ and elsewhere suggesting that Ibn Sīnā adhered to the ‘second kinematic model.’ As a corollary, a reconsideration of the attribution of the ten-intellect theory to Ibn Sīnā is called for. To begin with, Ibn Sīnā does not to my knowledge explicitly endorse the ten-intellect theory in Shifāʾ and in any of his other major works, such as Mabdaʾ, Najāt and Ishārāt. In fact, when he addresses the question of the number of separate intellects, he is always indecisive and deliberately leaves this issue unsettled.Footnote ⁷⁶ Even in the passage of Shifāʾ discussed earlier, where one would expect Ibn Sīnā to take sides on this issue, he presents these two models as hypotheses without revealing any preference for either one. True, in the last sentence Ibn Sīnā affirms that he has solved this problem “in the Mathematics,” but I was unable to find the exact passage alluded to by Ibn Sīnā, and this reference in any case raises more problems than it solves.Footnote ⁷⁷

Furthermore, whenever Ibn Sīnā describes the ‘first kinematic model’ consisting of ten separate intellects, he does so by way of report and ascribes it to other thinkers from whom he seems to want to distance himself. Hence, in Mabdaʾ, he attributes it vaguely “to the moderns” (al-mutaʾakhkhirūn) and to “a certain group of learned men” (qawm min al-afāḍil), while in Samāʾ, Ibn Sīnā uses an impersonal formula, “the opinion of he who thinks that…”.Footnote ⁷⁸ Clearly, Ibn Sīnā is not expressing his own opinion in these passages, but rather he is reporting other views for the sake of comprehensiveness.

In addition to these negative points, evidence for ascribing the ‘second kinematic model’ to Ibn Sīnā can be collected from Shifāʾ, Najāt, Ishārāt, and his commentary on Book Lambda. In these works, Ibn Sīnā states repeatedly that in order to understand the plurality of celestial motions, a separate principle must be posited for each corporeal body and for each motion. Ibn Sīnā puts forth various arguments to show that this must be the case. He begins by referring to the authority of some commentators, whom he does not mention by name, but who can be straightforwardly identified as Alexander and Themistius. According to them – or rather to Ibn Sīnā as he understands them – God is a principle of motion for the entire heaven, but in addition each orb has a mover proper to it.Footnote ⁷⁹ Ibn Sīnā then formulates an argument based on astronomical observations. The observed diversity of celestial motions and their differences in velocity indicate a plurality of movers. In this perspective, he provides more specific statements to the effect that one should posit one mover per motion and per orb: “It thus remains for each [of the orbs] to have an imitation of a separate, intellectual substance that belongs specifically to it; and that the [celestial] motions and their states will have differences that belong to them because of this…”Footnote ⁸⁰ And also: “It has become true to us through the art of the Almagest that [there are] numerous celestial motions and orbs, differing in direction, speed, and slowness. It thus follows necessarily that for each movement there exists a mover which is other than [the mover] existing for the other…”Footnote ⁸¹ Finally, Ibn Sīnā states:

In these passages, Ibn Sīnā explains that the multiplicity and particularity of the heavenly motions can only be accounted for by the existence of several movers. As he puts it, “for each movement there exists a mover,” thus apparently following Aristotle's theory that motion results from the contemplation of each orb for its respective unmoved mover. One may summarize Ibn Sīnā's view as follows: each orb has a celestial soul that looks up to a distinct separate intellect or unmoved mover, which it contemplates and desires, and which inspires its specific motion. Ultimately, these various intellects are responsible for the diversity of the planetary motions. There is no need in this picture for powers or emanations to be transmitted to the orbs by the planetary souls.Footnote ⁸³

It may be argued that the passages quoted above contain some ambiguity as to whether Ibn Sīnā ascribes a separate mover to the main orbs alone (aflāk kulliyya) or to all the spheres, including the subordinate or minor orbs (aflāk juzʾiyya). Yet this ambiguity vanishes if one recalls that Ibn Sīnā regards these minor devices (i.e., the eccentrics and epicycles) as bodies, as concrete entities possessing their own motion. As such, and to account for these motions, a separate mover has to be ascribed to each and every one of these minor orbs and spheres. In this connection, and as a proof of this, it is noteworthy that Ibn Sīnā entitles one section of the Metaphysics of both Mabdaʾ and Najāt, “On showing that each minor orb (falak juzʾī) possesses its own primary and separate mover.”

Ṭūsī's Sharḥ al-Ishārāt can be used to shed further light on this issue. Having discussed the theory that there are only nine celestial souls and intellects, and that the planets alone are ensouled, Ṭūsī pits this model against another model according to which the number of celestial souls and intellects corresponds to the number of all the celestial bodies and motions. And it is the latter model that Ṭūsī ascribes to Ibn Sīnā: “According to the school to which the master [al-shaykh, i.e., Ibn Sīnā] belongs, the number [of intellects] is [equal to] the number of orbs and planets, with the addition of one [the Agent Intellect].”Footnote ⁸⁴ Since Ṭūsī had previously fixed the number of spheres at 22 in his commentary – a number based on Ptolemy's Planetary Hypotheses – it would appear that he attributes to Ibn Sīnā a total of at least 22 orbs, motions, celestial souls, and separate movers.Footnote ⁸⁵

Finally, Mabdaʾ contains decisive evidence supporting the hypothesis that Ibn Sīnā adopted more than ten separate intellects. The passage in question appears immediately after Ibn Sīnā's description of the same two kinematic models that appear in the Metaphysics of Shifāʾ and that were already discussed. Because of the importance of this passage to understand Ibn Sīnā's cosmology and early Arabic cosmology in general, I have decided to give a complete translation of it:

Several significant points should be noted here. First, and quite surprisingly, Ibn Sīnā mentions epicycles (sing. kurat al-tadwīr) in his account of Aristotelian cosmology and seems to attribute these planetary hypotheses to the Stagirite. This anachronism suggests that the shaykh al-raʾīs had an inaccurate understanding of the specifics of the Aristotelian planetary models and of the development of ancient Greek astronomy. Ibn Sīnā does not mention the regular and counteracting orbs of Book Lambda 8, which in Aristotle's planetary system are all homocentric in spite of their different motions, but he instead ascribes to Aristotle planetary models that were developed several years after his death.Footnote ⁸⁷ This anachronism on the part of Ibn Sīnā is in fact symptomatic of much of the history of late-antique and medieval philosophy, which on the whole had a flawed perception of the development of the astronomical discipline. It is noteworthy that we find similar anachronisms in antiquity, with thinkers such as Nicomachus and Iamblichus ascribing the invention of eccentrics and epicycles to Pythagoras.Footnote ⁸⁸

Second, and equally important, is the fact that Ibn Sīnā places in opposition the Aristotelian and Ptolemaic kinematic models, which he calls schools of thought or doctrines (sing. madhhab), and which he regards as being incompatible with respect to the number of motions and the way in which the planets move through the heavens. In the Ptolemaic model he outlines, the planets move freely and transpierce (kharaqa) the epicycles, which themselves move freely through the deferents. On this view, neither the planets nor the epicycles are fixed, but rather enjoy an independent motion of their own, which need not be the same as the movements of the other celestial bodies. On the other hand, in the model Ibn Sīnā ascribes to Aristotle, the planets are fixed on their epicycles, which are themselves fixed on the deferents, so that no celestial body penetrates another.Footnote ⁸⁹ We know from other texts already referred to in this article that this is the theory Ibn Sīnā adhered to.

Furthermore, Ibn Sīnā intends to settle the question of the number of separate movers by referring to the astronomical views of Ptolemy and Aristotle. If one rejects the ten-intellect cosmology and the corollary theory of emanating powers from the planetary souls, then one must adhere to the alternative model, which posits as many movers as there are orbs and motions. One is then faced with the task of counting the motions and orbs in order to infer the number of separate movers. In this respect, Ibn Sīnā puts forth two main possibilities, one based on the Aristotelian model, the other on the Ptolemaic model, whose planetary hypotheses result in a different number of orbs and motions, and therefore of movers as well. Although he does not mention specific numbers in this passage of Mabdaʾ, the Ptolemaic position, Ibn Sīnā tells us, posits fewer motions and orbs than the Aristotelian one, with the implication that anyone relying on Ptolemy's planetary models would also posit fewer movers. This represents on Ibn Sīnā's view the principal difference between the two systems, since each otherwise rely on the eccentric and epicyclic theories.Footnote ⁹⁰

In this connection, and of crucial significance, is the fact that Ibn Sīnā considers the Stagirite's model to be the most likely: wa-al-aqrab ʿalā al-qiyās huwa madhhab al-faylasūf. This constitutes solid evidence that Ibn Sīnā on the one hand posited a separate principle for each motion and orb and on the other that he followed Aristotle's, rather than Ptolemy's, assessment of the number of orbs and motions. Yet it should be pointed out that Ibn Sīnā applied these Aristotelian tenets to a cosmology containing eccentrics and epicycles, which he endorsed and which he also boldly ascribed to the Stagirite. It is in this respect that one may accurately speak of the ‘second kinematic model’ as a ‘revised Aristotelian model,’ since it combines Aristotelian theories with the Ptolemaic planetary hypotheses in a veritable exegetical tour de force.Footnote ⁹¹

The key points that emerge from the previous paragraphs are the following. For both Ibn Sīnā and Ṭūsī, the number of separate intellects is equal to the number of celestial motions and orbs, including the minor orbs and spheres responsible for the particular motions of the planets. This means that each eccentric and epicycle is moved by a separate mover, with the total number of separate intellects depending on the number of eccentrics and epicycles posited to account for all the planetary motions. Consequently, the number of motions, orbs, celestial souls, and separate movers will be equal to each other, and will in any case be superior to ten. Moreover, according to Ibn Sīnā, this number can only be settled by astronomical observation and the planetary hypotheses posited to explain these phenomena, thus making astronomy a crucial ancillary to the metaphysical enterprise. In this respect, one perceives clearly the value of astronomy in Ibn Sīnā's metaphysics, as well as the importance of empirical knowledge and observation in solving problems that one would otherwise consider to be purely metaphysical, such as the number of the separate intellects. These points in turn show how faithfully Ibn Sīnā follows Aristotle's method and his views on the role of astronomy in the metaphysical inquiry at Metaphysics, XII.1073b7-17, where the number of unmoved movers is believed to hinge upon the astronomical observations concerning the number of motions and orbs. That Ibn Sīnā ascribed this method to Aristotle is evidenced independently by his statement in his Sharḥ Kitāb Ḥarf al-lām, that “he [Aristotle] sought the number of movers from the number of the orbs' motions” (thumma innahu yaṭlubu ʿadad al-muḥarrikīn min ʿadad ḥarakāt al-ukar).Footnote ⁹²

While the foregoing seems clear enough, one point remains ambiguous. Exactly how many orbs, motions, and movers did Ibn Sīnā posit? Did he endorse the number suggested by Aristotle in Book Lambda (47 or 55), as the previous passage in Mabdaʾ would suggest? If not, then in what way did he depart from this Aristotelian work? To my knowledge, Ibn Sīnā does not mention the exact number of heavenly motions, orbs, and movers he considers most likely to exist in any of his works. Yet some insight into this matter can be gained by a process of elimination. On the one hand, and as should be clear by now, Ibn Sīnā rejects the ten-intellect theory adopted by al-Fārābī and others. On the other hand, he prefers Aristotle's suggestion of 47 or 55 movers over the Ptolemaic number, which from Ṭūsī's Sharḥ al-Ishārāt may be said to be as low as 22, and which in any case must be smaller than 47 to justify Ibn Sīnā's preference. Finally, at the end of the aforementioned Mabdaʾ excerpt, Ibn Sīnā mentions the possibility that the real number may be higher than the one posited by Aristotle. This is undoubtedly a reference to the developments in planetary theory that had taken place in the Islamic world over a span of several centuries. Ibn Sīnā makes a similar suggestion in Refutation of Astrology, edited and analyzed by Y. Michot, when he states that the number of orbs is “close to sixty,”Footnote ⁹³ and that “it is possible that there are other orbs that have not yet been identified through observation.”Footnote ⁹⁴

Finally, a last point should be taken into account when calculating the total number of motions and separate principles: as was mentioned before, Ibn Sīnā ascribes to each planet a rotation around its own center, which is caused by its individual soul and not by the epicycle that carries it around. This means that each planet is endowed with its own principles of motion (i.e., a soul and a separate intellect), which are different from the souls and separate movers of the orbs associated with it. Hence, seven souls and separate intellects can be added to the final assessment, bringing the Aristotelian number of 55 occasionally mentioned by Ibn Sīnā to at least 62, and to a much higher number if additional orbs are ascribed to the fixed stars.Footnote ⁹⁵ All in all, then, and in spite of the difficulty of establishing an exact figure, it is clear that Ibn Sīnā posited a very high number of celestial orbs and spheres, souls, and intellects. In turn, this interpretation of Ibn Sīnā's cosmology invalidates the commonly made claim that he adopted al-Fārābī's scheme of the ten separate intellects.Footnote ⁹⁶

In what precedes, I tried to interpret as best I could Ibn Sīnā's disparate and occasionally problematic remarks on Aristotle's and Ptolemy's cosmologies and his own views on the matter. Nevertheless, certain discrepancies have resisted my best efforts to reconcile the loose ends of Ibn Sīnā's accounts. With regard to some of these points, such as the specifics of Aristotle's and Ptolemy's planetary models, it is clear that Ibn Sīnā had a somewhat confused understanding of the history of ancient astronomy, although this misunderstanding was influential in shaping his own solutions to some of the cosmological problems he addressed.Footnote ⁹⁷ With regard to other issues, one may hypothesize an evolution in Ibn Sīnā's thought to account for the apparent discrepancies.Footnote ⁹⁸ Leaving these questions aside, I wish to close this article with an examination of how Ibn Sīnā conceives of and explains the transition between the contemplative activity of the celestial souls and the physical motion of the celestial bodies.

MOTION, THE CELESTIAL BODY, AND THE CELESTIAL SOUL

Even though Ibn Sīnā seems to adopt a model in which each celestial component or body (including the eccentrics and epicycles) possesses its own soul and separate mover, he still has to account for the transition between the contemplative activity of the celestial souls and the actualization of motion in the celestial bodies. It should be noted that this issue is relevant to the two kinematic models discussed previously, since both models posit separate intellects or movers and celestial souls, albeit in different numbers.

According to Ibn Sīnā, celestial motion is the visible result of a long and complicated psychological process, which may broadly be divided into two stages, a contemplative one and a physical one. First, the celestial souls contemplate the perfection and infinite power of the separate movers, which ensure the perpetuity of the heavenly motions by acting as eternal objects of thought for the celestial souls.Footnote ⁹⁹ It is out of intellectual desire (shawq), will (irāda), and choice (ikhtiyār) – three concepts that are intimately connected and meant to stress rationality – that the celestial souls strive to imitate (iqtidāʾ, tashabbuh) the good and perfection of the separate intellects.Footnote ¹⁰⁰ But because these souls are closely associated with matter, and because the good and perfection they seek cannot be reached through motion,Footnote ¹⁰¹ their primary intention to imitate the higher principles becomes divided into particular and constantly renewed intentions that in turn correspond to an infinite series of motions.Footnote ¹⁰² Likewise, the primary intellectual conception (taṣawwur) that the souls have of the separate principles is converted into particular and constantly renewed conceptions (taṣawwurāt juzʾiyya), and their will is a particular and constantly renewed will (irāda mutajaddida juzʾiyya). It is these particular intentions and conceptions and this renewed will that cause the various and particular motions that together constitute the full revolutions of the celestial bodies.Footnote ¹⁰³ The propensity the celestial souls have toward particularization is all the more striking, since according to Ibn Sīnā, they cognize “changing things” (mutaghayyirāt) and “particulars” (juzʾiyyāt) and experience a continuous series of “acts of estimation” (awhām) and “imaginings” (takhayyulāt). The celestial souls are thus characterized by imagination (takhayyul) and estimation (wahm or quwwa mutawahhima) in addition to rationality. While these two faculties refer to different cognitive states in human psychology, in the case of the heavens, they seem to have a closely related meaning and to go hand in hand with the “conceptions” (taṣawwurāt) and rational activity of the celestial souls.Footnote ¹⁰⁴ In any case, the first stage underlying celestial motion may be said to consist in the transition from intellectual contemplation to the production of particular conceptions and motive intentions in the celestial souls.

In this connection, a conspicuous shortcoming of Ibn Sīnā's account should be highlighted. Although this point is ambiguous, Ibn Sīnā seems to endow the operation of the imaginative and estimative faculties with a role in producing the particular motive intentions of the celestial souls. Now, in human psychology, imagination and estimation belong to the inner senses (ḥawāss bāṭina), and they are closely linked to the exterior senses that provide them with the required images and data of external things.Footnote ¹⁰⁵ Yet in his major philosophical summae, Ibn Sīnā does not say anything about the possible existence of external senses in the celestial bodies, which would seem to be a prerequisite for imagination and estimation to operate. Moreover, he seems to closely connect these two inner senses with the rational faculty of the orbs.Footnote ¹⁰⁶

Various explanations come to mind to account for this problem. First, it is possible that Ibn Sīnā was undecided about what position to hold with respect to the exterior senses of the celestial bodies, i.e., whether vision and hearing should be ascribed to the orbs, a thesis which was upheld by earlier Arabic philosophers such as al-Kindī.Footnote ¹⁰⁷ He may have therefore decided not to treat this question expressly in Shifāʾ, an omission which is conspicuous in his cosmological discussions. We know that Ibn Sīnā rejected the theory of celestial senses and imagination and ascribed only the rational faculty to the heavenly bodies in some of his earlier treatises, and thus that he followed al-Fārābī on this question.Footnote ¹⁰⁸ The fact that the shaykh al-raʾīs articulates a theory of celestial imagination in Shifāʾ and other later works suggests a development in his reflection on this issue, which nonetheless may not have extended to the more minor, albeit related, problem of the exterior senses of the orbs.

Yet one can propose another interpretation, according to which the existence of the inner senses in the celestial bodies need not have as corollary the existence of the exterior senses. As I mentioned previously, Ibn Sīnā makes a visible effort to connect imagination and estimation with the rational souls of the orbs and possibly with their capacity to produce particular intentions and conceptions. Since these conceptions and intentions themselves arise out of the souls' will and rational contemplation, imagination and estimation seem to operate only insofar as they are turned toward the rational faculty. In the superlunary world, these inner senses are inscribed in what is essentially a vertical cognitive process, which proceeds downwards from the separate intellect to the rational soul to the inner senses, and which may therefore not involve the apprehension of lower entities by the exterior senses. Thus, sense perception could be dispensed with, and imagination fulfill a role comparable to the role it plays in al-Fārābī's theory of prophecy, where it allows the prophet-philosopher to translate into common symbols and images the intelligibles he has acquired by means of his rational faculty and through direct contact with the Agent Intellect. If this view is correct, then the particular conceptions of the celestial souls would arise out of their contemplation of the separate intellects and the First Cause through the mediation of their inner senses, a process which consequently need not rely in any way on sense perception.Footnote ¹⁰⁹

In brief, then, the celestial souls are a bridge between the purely immaterial existents and the corporeal faculties of the orbs and planets and ensure the conversion of intellection into motion. They possess both a rational faculty turned exclusively toward the separate intellects and the First and the faculties of imagination and estimation, which mediate between the rational souls and the celestial bodies. As a result, Ibn Sīnā frequently compares the superlunary and sublunary souls, claiming that the role they fulfill in producing bodily motion is somewhat similar in the two contexts.Footnote ¹¹⁰ Furthermore, he also compares the relation between the separate intellect, the celestial soul, and the celestial body to the relation between the Agent Intellect, the human soul, and the human body.Footnote ¹¹¹ Yet in spite of the sophistication of Ibn Sīnā's celestial psychology, one must conclude that it is marked by deep ambiguity with regard to the existence of the outer senses and the relation between the inner senses and the rational faculty, whose demarcation is not always clear.

In the second stage of the realization of celestial motion, the effects of this psychological process are somehow transmitted to the corporeal level and to the physical parts of the orbs. For as Ibn Sīnā explains, the souls' “celestial powers” (quwan samāwiyya) act through “the mediation of their bodies” (bi-wāsiṭati ajsāmihā).Footnote ¹¹² In order to refine his account of the relation between the celestial soul and the celestial body, Ibn Sīnā introduces a variety of philosophical notions, which as a corollary renders his theory of celestial kinematics more complex and difficult to grasp. Some of the key terms are mayl, maʿnā, ṭabīʿa, and fayḍ. Each one of these terms and concepts would require an exhaustive treatment of its own, which cannot be provided here. What is important for our purposes is that these concepts aim to qualify the activity of the celestial soul as a purveyor of motion and to explain how it can act on the celestial body. In an important and highly condensed passage of the Metaphysics of Shifāʾ, Ibn Sīnā explains that the motive power (quwwa) of the orbs acts through an inclination (mayl), which is an idea or intention (maʿnā) felt in the moving body.Footnote ¹¹³ This inclination thus represents an intermediary stage in the unfolding of motion, placed between the powers of the soul and the actualization of motion in the body. In the case of the heavens, this inclination is neither natural nor violent or constrained, but rather of a psychological kind, as it is in complete harmony with the will and desire of the celestial souls.Footnote ¹¹⁴

Perhaps more surprisingly, Ibn Sīnā goes on to say that this inclination or intention is also a nature (ṭabīʿa). This statement and the use of the term ṭabīʿa especially are at first glance quite odd, because in other passages Ibn Sīnā is adamant that celestial motion occurs by nature (bi-al-ṭabʿ), but that it is not natural (ṭabīʿī) and thus not connected with sublunary nature (ṭabīʿa).Footnote ¹¹⁵ The fundamental idea motivating this claim is that natural motion, i.e., the motion of the sublunary elements, is dictated both by their rectilinear inclination and by their natural place in the world. Natural motion is thus the return of an element to its natural place or state. When the elements reach their natural place, their rectilinear motion comes to an end. But since there is no natural place for the heavenly bodies, which are constantly revolving around their own center, their motion cannot be said to be natural in the sense applied to sublunary bodies. Instead of nature, then, the principles moving the heavens are will and soul, concepts which Ibn Sīnā generally opposes to nature, but which he here seems to connect with a special celestial nature. One detects in these passages the influence of Alexander of Aphrodisias' Mabādiʾ, which also describes a special celestial nature (ṭabīʿa) that is closely related to the celestial souls.Footnote ¹¹⁶

Ibn Sīnā provides an important clarification in the same passage on this special “nature” of the heavenly bodies: it is “an emanation (fayḍ) from a soul,” he writes, “that is renewed in accordance with the soul's act of acquiring representation.”Footnote ¹¹⁷ Now, Ibn Sīnā does not explain what kind of emanations the celestial souls produce, nor does he explain what function and end they serve. Moreover, it is unclear whether these emanations are directed at the celestial bodies themselves or toward other entities, such as the sublunary existents. As is well known, fayḍ is a term that appears frequently in Ibn Sīnā's works in relation to doctrines of emanation and causation, a topic about which much literature exists.Footnote ¹¹⁸ Yet the passage under consideration from the Metaphysics of Shifāʾ does not deal with the creation of the heavenly entities, but with bodily motion, and more specifically with the question of how the celestial souls cause this motion. For this reason, fayḍ may possess here a technical connotation that differs from its usual meaning in a creationist context.

This need not be the case, however, for other passages seem to define celestial motion as a kind of creation or causation exercised by a higher entity on a lower one, i.e., by the celestial soul on the celestial body. In Mabdaʾ, Ibn Sīnā explains that the renewal of motions in the celestial body is a result of the renewal of particular acts of willing and conceptions by the celestial soul, and that this process occurs by way of generation or renewal (ḥudūth), not by way of permanence (thabāt).Footnote ¹¹⁹ Hence, the motion of the outermost orb, for instance, is caused by its soul producing inclination after inclination in the outermost celestial body.Footnote ¹²⁰ In a passage of the Physics of Shifāʾ already noted by Hasnawi, Ibn Sīnā states that motion is produced by or emanates from a mayl, which in the context of Ibn Sīnā's cosmology must be a ‘psychological mayl,’ which is directly connected with the celestial souls.Footnote ¹²¹ More evocatively, Ibn Sīnā in Najāt specifies that celestial motion is engendered (kāʾina),Footnote ¹²² while in Ishārāt, one finds a striking connection between emanationist concepts and celestial motion:

The foregoing references and quotations illustrate vividly Ibn Sīnā's willingness to use causative and emanationist terms – commonly used in his discussions of how the existents proceed from the First and the separate intellects – in his descriptions of how celestial motion is produced by the celestial souls. Accordingly, terms from the roots f-y-ḍ, k-w-n, b-ʿ-th, and ḥ-d-th are used to describe this process. This in turn suggests that Ibn Sīnā conceived of celestial motion as a kind of creation or causation, involving higher, active principles (the separate intellects and the celestial souls) and a lower, passive one (the celestial body).

It should be noted that this language of emanation or causation with respect to the celestial bodies is also used by Ibn Sīnā in another yet related context to express their influence on the sublunary world as a result of their various motions. This is clearly the purpose intended in Najāt, when Ibn Sīnā states that “coldness and heat emanate [tafīḍu] from the celestial powers [quwan]”Footnote ¹²⁴ and in R. fī al-jawhar al-nafīs, when he states that “there emanates from the planet Venus a power [tafīḍu minhu quwwa] that produces coldness…”Footnote ¹²⁵ Hence, we find in Ibn Sīnā's works the two concepts of emanation (fayḍ) and celestial power (quwwa) combined to express either the process of the generation of motion by the celestial soul and its transmission to the celestial body or the influence that the celestial bodies exercise on the sublunary world as a result of these motions.

Another important function of the emanationist terminology used by Ibn Sīnā is that it establishes a parallel between the celestial and sublunary bodies and more specifically between celestial and animal motion, for Ibn Sīnā also uses fayḍ, inbiʿāth, and other cognate terms to describe the motive powers of the animal body. In Ishārāt, Ibn Sīnā explains that the animal muscles possess motive forces (sing. quwwa muḥarrika) that obey the orders coming from the animal soul, and in his K. al-Nafs, he defines the animal soul as “the thing from which acts emanate [tafīḍu]” and the “principle that produces acts [mabdaʾ li-ṣudūr al-afāʿīl].”Footnote ¹²⁶ Closely related to this idea is Ibn Sīnā's explanation in the Physics section of Najāt that an influence (taʾthīr) comes out of (yasnaḥa minhā) the soul of animated beings and moves the corporeal parts of the animal.Footnote ¹²⁷ Interestingly, a similar statement reappears in the Metaphysics of Shifāʾ in the context of Ibn Sīnā's account of the motion of the orbs, thus showing that this interpretive framework can be applied with equal efficiency to the orbs and sublunary animals.Footnote ¹²⁸ With regard to the latter, Ibn Sīnā also mentions the “emanating influences” (sing. taʾthīr fāʾiḍ) in K. al-Ḥayawān to explain how the motive and sensual qualities of the limbs and muscles of animals are directed by the brain through the intermediacy of the nervous system.Footnote ¹²⁹ As Hasnawi notes: “Les mots de la famille ṣadara, inbaʿatha, et même fāḍa figurent couramment […] dans les traités physiques d'Avicenne lorsqu'il s'agit de décrire l'émanation d'une qualité, d'une action, ou d'un mouvement à partir d'une puissance, qu'elle soit physique ou psychique.”Footnote ¹³⁰ Hence, Ibn Sīnā employs the terms fāḍa, taʾthīr, inbaʿatha, and ṣadara ʿan interchangeably in a sublunary and superlunary context to explain how bodily movements are produced as a result of powers emitted by the soul. Moreover, these terms underscore the fact that each individual motion may be seen as something generated (ḥudūth or kāʾin) by a principle (mabda'), identified with either the celestial soul or the animal soul.

On the basis of the foregoing, one notices not only the common terminology but also the closeness of the kinematic model Ibn Sīnā articulates with regard to celestial and sublunary beings. When it comes to animated beings, whether these consist of the planets or perishable animals, the soul initiates motion through its powers by sending influences or stimuli to the corporeal parts to which it is associated. In the heavenly context, these emissions are sent by the celestial souls of the planets, orbs, and spheres to their corporeal parts, while in the case of animals they are transmitted from the animal soul to the muscles and limbs. These parallels help to explain why Ibn Sīnā frequently compares the role of the sublunary and superlunary souls in his works, going so far as to say that they move their bodies in a similar fashion.Footnote ¹³¹

The application of emanationist terminology to describe the orbs' psychological activity was probably intended by Ibn Sīnā to account for how abstract psychological and intellective processes can ultimately result in the motion of corporeal entities. Part of Ibn Sīnā's solution consists in bridging the immaterial and physical aspects of motion through the use of this causative or emanationist terminology, just as this same terminology is used to cover the ontological gap between the separate intellects and the orbs and to explain how the latter proceed from the former. Moreover, it is notable that Ibn Sīnā's kinematic account draws on features proper to both procession and reversion: while the celestial souls' contemplation of God and the intellects belongs to the process of reversion toward the First, the powers emanating from the celestial souls on the celestial bodies and subsequently on the sublunary world parallel the causative activity of the separate intellects and are inscribed in the downward movement away from the First that expresses procession. In combining and reconciling the two concepts of procession and reversion, Ibn Sīnā's account of celestial motion is thoroughly integrated in the larger metaphysical program he elaborated.Footnote ¹³² His interpretation of Aristotelian cosmology, particularly with regard to celestial kinematics, as well as his own theories on the subject, is fully inscribed in a Neoplatonizing-Aristotelian tradition that combines the two concepts of ascension toward the First and procession away from the First as its main interpretive framework.

SUMMARY AND HYPOTHETICAL RECONSTRUCTION OF IBN SĪNĀ'S THEORY OF CELESTIAL KINEMATICS

In light of the various results reached in the course of this analysis, one may propose the following hypothetical reconstruction of Ibn Sīnā's kinematic theory. Each planetary system (the system of Mars, of the moon, etc.) is composed of one main orb, itself containing a planet and various other minor bodies, i.e., concentric and/or eccentric orbs and epicycle spheres, with the exception of the orb of the sun, whose astronomical model puzzled Ibn Sīnā.Footnote ¹³³ Each entity within a system is a spherical body that is ensouled and which furthermore possesses its own separate principle of motion, i.e. a separate intellect that acts as an unmoved mover and toward which it orients its contemplation. Ibn Sīnā regards this multiplicity of celestial souls and separate movers – which may be as high as sixty or even higher – as a necessary requisite to account for the diversity of motions that characterize the orbs and planets. Indeed, while the constant circular motion of the heavens depends on its having a common and unchanging object of thought, i.e., the First Cause,Footnote ¹³⁴ the particular motions of the orbs can only be explained if one posits a separate mover specific to each one of them. It is remarkable that Ibn Sīnā considered all of the points enumerated above as genuinely Aristotelian and that he regarded himself as merely following a well-established Peripatetic cosmological tradition.

The process by virtue of which the specific celestial motions are actualized represents a complicated and somewhat obscure facet of Ibn Sīnā's cosmology. Each celestial soul, whether of the main orbs, of the smaller concentric and eccentric orbs, of the epicycle spheres, or of the planets and stars, contemplates its separate mover or intellect, which acts as the eternal final cause of its motion.Footnote ¹³⁵ At this level of intellectual activity, the conception and first intention of the celestial souls have not yet been particularized into specific intentions and conceptions. The process of generating particular motive intentions is made possible presumably through the special imaginative and estimative faculties of the celestial souls, which distinguishes their activity from that of the separate intellects. These motive intentions are then transmitted or emanated in the form of powers or influences to the corresponding corporeal parts of the orbs and planets, a process that ultimately results in the actualization of the particular motions of each celestial body.

Ibn Sīnā introduces several different concepts to explain the transition that motion undergoes from the intellectual stage, to the psychological stage, and finally to the corporeal stage, a multi-layered process which ends with the phenomenal movements of the planets. Together with their rational soul and their imaginative and estimative faculties, the celestial bodies possess a motive power (quwwa muḥarrika) that acts through their inclination (mayl) and nature (ṭabīʿa), so that there is a perfectly harmonious overlap between what they desire and will and their natural disposition. The chief function of these concepts is to explain how motion, which originates in the celestial soul, can subsequently be transmitted from the spiritual to the corporeal plane, without any contradiction or constraint affecting the substance of the celestial bodies. There can be little doubt that Ibn Sīnā developed these concepts partly as an attempt to elucidate this difficult cosmological problem.

This complex model of celestial kinematics, which draws imaginatively on Aristotelian, Ptolemaic, Neoplatonic, and possibly Galenic sources, enables Ibn Sīnā to account causally for the variety and plurality of planetary motions in a manner that systematically brings together astronomy, physics, and metaphysics. While the fundamental principles of motion in this picture are intellect, soul, and, to a lesser extent, imagination and estimation, which makes physics and metaphysics the chief cosmological sciences, Ibn Sīnā nonetheless strives to coherently explain how these principles may be integrated in the general astronomical framework inherited from Ptolemy, and he moreover introduces other physical notions derived from his observation of sublunary animals.