Philosophy
According to Averroes, there is no conflict between religion and philosophy, rather that they are different ways of reaching the same truth. He believed in the creating of the universe by an all perfect god contrary to Avicenna's ideology which was the universe is eternal since god doesn't have specific knowledge(this is the view of Avicenna). He also held that the soul is divided into two parts, one individual and one divine; while the individual soul is not eternal, all humans at the basic level share one and the same divine soul. Averroes has two kinds of Knowledge of Truth. The first being his knowledge of truth of religion being based in faith and thus could not be tested, nor did it require training to understand. The second knowledge of truth is philosophy, which was reserved for an elite few who had the intellectual capacity to undertake this study.
The concept of "existence precedes essence", a key foundational concept of existentialism, can also be found in the works of Averroes, as a reaction to Ibn Sina's concept of "essence precedes existence". Averroes's most famous original philosophical work was
The Incoherence of the Incoherence, a rebuttal to Al-Ghazali's
The Incoherence of the Philosophers. In medieval Europe, his school of philosophy known as Averroism exerted a strong influence on Jewish philosophers such as Gersonides and Maimonides, and was opposed by Christian philosophers such as Thomas Aquinas.
Astronomy
At the age of 25, Averroes conducted astronomical observations near Marrakech, Morocco, during which he discovered a previously unobserved star.
In astronomical theory, Averroes rejected the eccentric deferents introduced by Ptolemy. He rejected the Ptolemaic model and instead argued for a strictly concentric model of the universe. He wrote the following criticism on the Ptolemaic model of planetary motion:
"To assert the existence of an eccentric sphere or an epicyclic sphere is contrary to nature. [...] The astronomy of our time offers no truth, but only agrees with the calculations and not with what exists."
Averroes also argued that the Moon is opaque and obscure, and has some parts which are thicker than others, with the thicker parts receiving more light from the Sun than the thinner parts of the Moon. He also gave one of the first descriptions on sunspots.
Celestial mechanics
In celestial mechanics, while discussing the celestial spheres, Averroes rejected John Philoponus' 'anti-Aristotelian' solution to his refutation of Aristotelian celestial dynamics, and instead restored Aristotle's law of motion by adopting the 'hidden variable' approach to resolving apparent refutations of parametric laws that posits a previously unaccounted variable and its value(s) for some parameter, thereby modifying the predicted value of the subject variable. For, he posited a non-gravitational, previously unaccounted, inherent resistance to motion, as hidden within the celestial spheres. This was a non-gravitational inherent resistance to motion of superlunary quintessential matter, whereby
R > 0 even when there is neither any gravitational, nor any media resistance, to motion.
Hence, in refuting the prediction of Aristotelian celestial dynamics:
- :: [ (i) v ? F/R & (ii) F > 0 & (iii) R = 0 ] entail v is infinite
the alternative logic of Averroes' solution was to reject its third premise "R = 0" instead of rejecting its first premise as Philoponus had.
Thus Averroes most significantly revised Aristotle's law of motion "v ? F/R" into "v ? F/M" for the case of celestial motion with his auxiliary theory of what may be called celestial inertia
M, whereby
R = M > 0. But Averroes restricted inertia to celestial bodies and denied sublunar bodies have any inherent resistance to motion other than their gravitational (or levitational) inherent resistance to violent motion, just as in Aristotle's original sublunar physics.
However, Thomas Aquinas, also a student of Aristotelianism, rejected this denial of sublunar inertia and extended Averroes' innovation in the celestial physics of the spheres to all sublunar bodies. He posited all bodies universally have a non-gravitational inherent resistance to motion constituted by their magnitude or mass. In his
Systeme du Monde, the pioneering historian of medieval science Pierre Duhem, stated:
"For the first time we have seen human reason distinguish two elements in a heavy body: the motive force, that is, in modern terms, the weight; and the moved thing, the corpus quantum, or as we say today, the mass. For the first time we have seen the notion of mass being introduced in mechanics, and being introduced as equivalent to what remains in a body when one has suppressed all forms in order to leave only the prime matter quantified by its determined dimensions. Saint Thomas Aquinas's analysis, completing Ibn Bajja's, came to distinguish three notions in a falling body: the weight, the mass, and the resistance of the medium, about which physics will reason during the modern era....This mass, this quantified body, resists the motor attempting to transport it from one place to another, stated Thomas Aquinas."See Duhem's analysis of this development - St Thomas Aquinas and the Concept of Mass- on p378-9 of Roger Ariew's 1985 Medieval Cosmology, an extract also to be found online at . But Duhem notably fails to accord Averroes his originating innovatory due compared with Avempace and Aquinas, as more clearly accorded by Sorabji's 1988 Matter, Space and Motion p284. Duhem was originally refuting Mach's claim in his Science of Mechanics that Newton first discovered the crucial notion of inertial resistant mass in the 17th century. Mach's error was surprisingly still repeated by the self-professed 'Duhemian gradualist' Bernard Cohen a century later in his 2002 The Cambridge Companion to Newton article Newton's concepts of force and mass, p59.
Some five centuries after Averroes' and Aquinas' innovations, it was Johannes Kepler who first dubbed this non-gravitational inherent resistance to motion in all bodies universally 'inertia'. Hence the crucial notion of 17th century early classical mechanics of a resistant force of inertia inherent in all bodies was born in the heavens of medieval astrophysics, in the Aristotelian physics of the celestial spheres, rather than in terrestrial physics or in experiments.
However, having discounted the possibility of any resistance due to a contrary inclination to move in any opposite direction or due to any external resistance, in concluding their impetus was therefore not corrupted by any resistance, Jean Buridan also discounted any inherent resistance to motion in the form of an inclination to rest within the spheres themselves, such as the inertia posited by Averroes and Aquinas. For otherwise, that resistance would destroy their impetus, as the anti-Duhemian historian of science Annaliese Maier maintained the Parisian impetus dynamicists were forced to conclude, because of their belief in an inherent
inclinatio ad quietem (tendency to rest) or inertia in all bodies. But in fact, contrary to that inertial variant of Aristotelian dynamics, according to Buridan, prime matter does not resist motion.
Law and jurisprudence
As a Qadi (judge), Averroes wrote the
Bid?yat al-Mujtahid wa Nih?yat al-Muqtasid, a Maliki legal treatise dealing with Sharia (law) and Fiqh (jurisprudence) which, according to Al-Dhahabi in the 13th century, was considered the best treatise ever written on the subject. Averroes's summary the opinions (
fatwa) of previous Islamic jurists on a variety of issues has continued to influence Islamic scholars to the present day, notably Javed Ahmad Ghamidi. While Averroes himself claimed that women in Islam were equal to men in all respects and possessed equal capacities to shine in peace and in war, he summarized the opinions of previous jurists and Imams on the status of women's testimony in Islam as follows:
"There is a general consensus among the jurists that in financial transactions a case stands proven by the testimony of a just man and two women on the basis of the verse: ‘If two men cannot be found then one man and two women from among those whom you deem appropriate as witnesses’. However; in cases of Hudud, there is a difference of opinion among our jurists. The majority say that in these affairs the testimony of women is in no way acceptable whether they testify alongside a male witness or do so alone. The Zahiris on the contrary maintain that if they are more than one and are accompanied by a male witness, then owing to the apparent meaning of the verse their testimony will be acceptable in all affairs. Imam Abu Hanifah is of the opinion that except in cases of Hudud and in financial transactions their testimony is acceptable in bodily affairs like divorce, marriage, slave-emancipation and raju‘ [restitution of conjugal rights]. Imam Malik is of the view that their testimony is not acceptable in bodily affairs. There is however a difference of opinion among the companions of Imam Malik regarding bodily affairs which relate to wealth like advocacy and will-testaments which do not specifically relate to wealth. Consequently, Ash-hab and Ibn Majishun accept two male witnesses only in these affairs, while to Malik Ibn Qasim and Ibn Wahab two female and a male witness are acceptable. As far as the matter of women as sole witnesses is concerned, the majority accept it only in bodily affairs, about which men can have no information in ordinary circumstances like the physical handicaps of women and the crying of a baby at birth."
He also discussed Islamic economic jurisprudence, particularly the concept of Riba (usury). He reported that Ibn ‘Abbas, a sahaba (companion) of Muhammad, did not accept
Riba al-Fadl (interest in excess) because, according to him, the Prophet Muhammad had clarified that there was no Riba except in credit. He also discussed the role of Islamic criminal jurisprudence in the Islamic dietary laws in regards to the consumption of alcohol. He stated that physical punishment for alcoholic consumption was not originally established as part of the Sharia in Muhammad's time but was later decided by the
Shura (consultive council) of the Rashidun Caliphate. He wrote:
"The general opinion in this regard is based on the consultation of ‘Umar (rta) with the members of his Shura. The session of this Shura took place during his period when people started indulging in this habit more frequently. ‘Ali (rta) opined that, by analogy with the punishment of Qadhf, its punishment should also be fixed at eighty stripes. It is said that while presenting his arguments, he had remarked: ‘When he [— the criminal —] drinks, he will get intoxicated and once he gets intoxicated, he will utter nonsense; and once he starts uttering nonsense, he will falsely accuse other people’."
Logic
Averroes was the last major Muslim logician from Al-Andalus. He is known for writing the most elaborate commentaries on Aristotelian logic.
Medicine
As a physician, Averroes wrote twenty treatises on Arabic medicine, including a seven-volume medical encyclopedia entitled
Kit?bu’l Kulliy?t f? al-Tibb (
General Rules of Medicine), better known as
Colliget in Latin. This encyclopedic work was completed at some time before 1162 and elaborated on physiology, general pathology, diagnosis, materia medica, hygiene and general therapeutics. He argued that no one can suffer from smallpox twice, and fully understood the function of the retina. He improved on Alhazen's
Book of Optics (1021) which, though providing a largely correct optical theory on vision, incorrectly assumed the lens of the eye to be the organ of sight. Averroes corrected this by showing that sight is the function of the retina.
His
Colliget was largely overshadowed by the earlier medical encyclopedias,
Continents by Muhammad ibn Zakariya ar-Razi (Rhazes) and
The Canon of Medicine by Ibn Sina (Avicenna). As a result, Averroes' fame as a physician was eclipsed by his own fame as a philosopher. His
Kulliy?t was translated into Latin by the Jewish translator Bonacosa in the late 13th century and again by Syphorien Champier in
circa 1537, and it was also translated into Hebrew twice. Max Meyerhof notes that the prototypes for the physician-philosophers that predominated in Spain were "Ibn Zuhr (Avenzoar) and Averroes (Averroes)".
Averroes discussed the topic of human dissection and autopsy. Although he never undertook human dissection, he was aware of it being carried out by some of his contemporaries, such as Ibn Zuhr (Avenzoar), and appears to have supported the practice. Averroes stated that the "practice of dissection strengthens the faith" due to his view of the human body as "the remarkable handiwork of God in his creation." Despite his criticism of Al-Ghazali's theological views, Averroes agreed with him on the issue of anatomy and dissection, and wrote:
"Whoever has been occupied with the science of anatomy/dissection (tashrfh) has increased his belief in God."
In urology, Averroes identified the issues of sexual dysfunction and erectile dysfunction, and was among the first to prescribe medication for the treatment of these problems. He used several methods of therapy for this issue, including the single drug method where a tested drug is prescribed, and a "combination method of either a drug or food." Most of these drugs were oral medication, though a few patients were also treated through topical or transurethral means.
In neurology and neuroscience, Averroes suggested the existence of Parkinson's disease, and in ophthalmology and optics, he was the first to attribute photoreceptor properties to the retina. In his
Colliget, he was also the first to suggest that the principal organ of sight might be the arachnoid membrane (
aranea). His work led to much discussion in 16th century Europe over whether the principal organ of sight is the traditional Galenic crystalline humour or the Averroist
aranea, which in turn led to the discovery that the retina is the principal organ of sight.
Music theory
As an Arabic music theorist, Averroes contributed to music theory with his commentary on Aristotle's
On the Soul, where Averroes dealt perspicuously with the theory of sound. This text was translated into Latin by Michael Scot (d. 1232).
Physics
In Averroes' commentary on Aristotle's
Physics, he commented on the theory of motion proposed by Ibn Bajjah (Avempace) in Text 71, and also made his own contributions to physics, particularly mechanics. Averroes was the first to define and measure force as "the rate at which work is done in changing the kinetic condition of a material body" and the first to correctly argue "that the effect and measure of force is change in the kinetic condition of a materially resistant mass." It seems he was also the first to introduce the notion that bodies have a (non-gravitational) inherent resistance to motion into physics, subsequently first dubbed 'inertia' by Johannes Kepler. But he only attributed it to the superlunary celestial spheres, and in order to explain why they do not move with infinite speed as was predicted by the application of Aristotle's general law of motion
v ? F/R to celestial motion, given the assumption that the spheres have movers and thus
F > 0, but no resistance to their motion, whereby
R = 0.
John Philoponus had earlier rejected Aristotle's theory of motion because of this celestial empirical refutation in favour of his alternative theory
v ? F - R that avoided it because
v is finite even when
R = 0 and when
F > 0 and is finite. But
contra Philoponus, Averroes restored it by positing inertia instead, whereby
R > 0 even in the absence of any external resistance to motion and of any inherent gravitational resistance, as in the quintessential heavens in Aristotelian cosmology. But Averroes denied sublunar bodies have inertia, and it was Thomas Aquinas, also a student of Aristotelianism, who extended this inherent force to terrestrial bodies as well, thus also rejecting Aristotle's prediction that the speed of gravitational fall of all bodies in a vacuum would be infinite because there would be no resistance to motion in the absence of an external resistant medium (i.e.
R = 0). For Aristotle had assumed the
only inherent resistance to motion in bodies is that of gravity, without which bodies would not inherently resist any motion, and which does not resist gravitational (i.e. 'natural') motion where it acts as the motor rather than as a brake as it does in violent motion. The Averroes-Aquinas notion of inertia was eventually adopted by Kepler, but not by scholastic Aristotelian impetus dynamics nor Galileo Galilei who maintained like Jean Buridan, for example, that prime matter does not inherently resist any motion and so is indifferent to motion or rest. It eventually became the central concept of Newton's dynamics in its notion of the inherent force of inertia in all bodies, with the minor revision that the force of inertia resists all motion
except for uniform straight motion, a purely fictitious ideal motion whose perseverance it would cause. But Newton's inherent force of inertia resists all actual motion, given it is all accelerated motion in the Newtonian cosmos populated by many gravitationally attractive massive bodies. Thus on this analysis Averroes is creditable with one of the two most crucial innovations in the history of the development of Aristotelian dynamics into Newtonian dynamics, namely its two auxiliary notions of the force of impetus and of the force of inertia.
Politics
Averroes did not have access to any text of Aristotle's
Politics. As a substitute for this, he commented on Plato's
The Republic, arguing that the ideal state there described was the same as the original constitution of the Islamic Caliphate, as well as the Almohad state of Ibn Tumart. He also believed that a wise philosopher should be commander and chief of a nation.
Averroes also claimed that women were equal to men in all respects and possessed equal capacities to shine in peace and in war, citing examples of female warriors among the Arabs, Greeks and Africans to support his case. In Muslim history, examples of notable female Muslims who fought as soldiers or generals included Nusaybah Bint k’ab Al Maziniyyah, Aisha, Kahula and Wafeira, and Um Umarah.
Psychology
H. Chad Hillier writes the following on Averroes's contributions to psychology:
There is evidence of some evolution in Averroes's thought on the intellect, notably in his Middle Commentary on De Anima where he combines the positions of Alexander and Themistius for his doctrine on the material intellect and in his Long Commentary and the Tahafut where Averroes rejected Alexander and endorsed Themistius’ position that "material intellect is a single incorporeal eternal substance that becomes attached to the imaginative faculties of individual humans." Thus, the human soul is a separate substance ontologically identical with the active intellect; and when this active intellect is embodied in an individual human it is the material intellect. The material intellect is analogous to prime matter, in that it is pure potentiality able to receive universal forms. As such, the human mind is a composite of the material intellect and the passive intellect, which is the third element of the intellect. The passive intellect is identified with the imagination, which, as noted above, is the sense-connected finite and passive faculty that receives particular sensual forms. When the material intellect is actualized by information received, it is described as the speculative (habitual) intellect. As the speculative intellect moves towards perfection, having the active intellect as an object of thought, it becomes the acquired intellect. In that, it is aided by the active intellect, perceived in the way Aristotle had taught, to acquire intelligible thoughts. The idea of the soul's perfection occurring through having the active intellect as a greater object of thought is introduced elsewhere, and its application to religious doctrine is seen. In the Tahafut, Averroes speaks of the soul as a faculty that comes to resemble the focus of its intention, and when its attention focuses more upon eternal and universal knowledge, it becomes more like the eternal and universal. As such, when the soul perfects itself, it becomes like our intellect.
Averroes succeeded in providing an explanation of the human soul and intellect that did not involve an immediate transcendent agent. This opposed the explanations found among the Neoplatonists, allowing a further argument for rejecting of Neoplatonic emanation theories. Even so, notes Davidson, Averroes’s theory of the material intellect was something foreign to Aristotle.