This contact with “the philosophy of the ancients” (as Greek philosophy was often referred to by Muslim scholars) had a profound effect on his intellectual development, and led him to write hundreds of original treatises of his own on a range of subjects ranging from metaphysics
, to medicine
, and further afield to more practical topics like perfumes
In the field of mathematics, al-Kindi played an important role in introducing Indian numerals
to the Islamic and Christian world
He was a pioneer in cryptanalysis
and devised several new methods of breaking ciphers.[11
Using his mathematical and medical expertise, he was able to develop a scale that would allow doctors to quantify the potency of their medication.
The central theme underpinning al-Kindi’s philosophical writings is the compatibility between philosophy and other “orthodox” Islamic sciences, particularly theology
. And many of his works deal with subjects that theology had an immediate interest in. These include the nature of God, the soul
and prophetic knowledge
But despite the important role he played in making philosophy accessible to Muslim intellectuals, his own philosophical output was largely overshadowed by that of al-Farabi
and very few of his texts are available for modern scholars to examine.
Al-Kindi was born in Kufa
to an aristocratic family of the Kinda
tribe. His father was the governor of Kufa, and al-Kindi received his preliminary education there. He later went to complete his studies in Baghdad
, where he was patronized by the Abbasid
. On account of his learning and aptitude for study, al-Ma’mun appointed him to House of Wisdom
, a recently established centre for the translation of Greek
philosophical and scientific texts, in Baghdad. He was also well known for his beautiful calligraphy
, and at one point was employed as a calligrapher by al-Mutawakkil
When al-Ma’mun died, his brother, al-Mu’tasim became Caliph. Al-Kindi’s position would be enhanced under al-Mu’tasim, who appointed him as a tutor to his son.
But on the accession of al-Wathiq
, and especially of al-Mutawakkil
, al-Kindi’s star waned. There are various theories concerning this: some attribute al-Kindi’s downfall to scholarly rivalries at the House of Wisdom; others refer to al-Mutawakkil’s often violent persecution of unorthodox Muslims (as well as of non-Muslims); at one point al-Kindi was beaten and his library temporarily confiscated. Henry Corbin
, an authority on Islamic studies, says that in 873, al-Kindi died “a lonely man”, in Baghdad during the reign of Al-Mu’tamid
After his death, al-Kindi’s philosophical works quickly fell into obscurity and many of them were lost even to later Islamic scholars and historians. Felix Klein-Franke suggests a number of reasons for this: aside from the militant orthodoxy of al-Mutawakkil, the Mongols
also destroyed countless libraries during their invasion
. However, he says the most probable cause of this was that his writings never found popularity amongst subsequent influential philosophers such as al-Farabi
, who ultimately overshadowed him.
Al-Kindi was a master of many different areas of thought. And although he would eventually be eclipsed by names such as al-Farabi
, he was held to be one of the greatest Islamic
philosophers of his time. The Italian Renaissance scholar Geralomo Cardano
(1501–1575) considered him one of the twelve greatest minds of the Middle Ages.
According to Ibn al-Nadim, al-Kindi wrote at least two hundred and sixty books, contributing heavily to geometry
(thirty-two books), medicine and philosophy (twenty-two books each), logic
(nine books), and physics
His influence in the fields of physics, mathematics, medicine, philosophy and music were far-reaching and lasted for several centuries. Although most of his books have been lost over the centuries, a few have survived in the form of Latin
translations by Gerard of Cremona
, and others have been rediscovered in Arabic manuscripts; most importantly, twenty-four of his lost works were located in the mid-twentieth century in a Turkish library.
His greatest contribution to the development of Islamic philosophy was his efforts to make Greek thought both accessible and acceptable to a Muslim audience. Al-Kindi carried out this mission from the House of Wisdom
(Bayt al-Hikma), an institute of translation and learning patronized by the Abbasid
Caliphs, in Baghdad.
As well as translating many important texts, much of what was to become standard Arabic philosophical vocabulary originated with al-Kindi; indeed, if it had not been for him, the work of philosophers like Al-Farabi
, and al-Ghazali
might not have been possible.
In his writings, one of al-Kindi’s central concerns was to demonstrate the compatibility between philosophy and natural theology
on the one hand, and revealed or speculative theology
on the other (though in fact he rejected speculative theology). Despite this, he did make clear that he believed revelation was a superior source of knowledge to reason because it guaranteed matters of faith that reason could not uncover. And while his philosophical approach was not always original, and was even considered clumsy by later thinkers (mainly because he was the first philosopher writing in the Arabic language), he successfully incorporated Aristotelian
and (especially) neo-Platonist
thought into an Islamic philosophical framework. This was an important factor in the introduction and popularization of Greek philosophy in the Muslim intellectual world.
Al-Kindi took his view of the solar system from Ptolemy
, who placed the Earth at the centre of a series of concentric spheres, in which the known heavenly bodies (the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and the stars) are embedded. In one of his treatises on the subject, he says that these bodies are rational entities, whose circular motion is in obedience to and worship of God. Their role, al-Kindi believes, is to act as instruments for divine providence. He furnishes empirical evidence
as proof for this assertion; different seasons are marked by particular arrangements of the planets and stars (most notably the sun); the appearance and manner of people varies according to the arrangement of heavenly bodies situated above their homeland.
However, he is ambiguous when it comes to the actual process by which the heavenly bodies affect the material world. One theory he posits in his works is from Aristotle, who conceived that the movement of these bodies causes friction in the sub-lunar region, which stirs up the primary elements of earth, fire, air and water, and these combine to produce everything in the material world. An alternative view found his treatise On Rays
is that the planets exercise their influence in straight lines. In each of these, he presents two fundamentally different views of physical interaction; action by contact and action at a distance. This dichotomy is duplicated in his writings on optics
Some of the notable astrological works by al-Kindi include:
The Book of the Judgement of the Stars, including The Forty Chapters, on questions and elections.
On the Stellar Rays.
Several epistles on weather and meteorology, including De mutatione temporum, (“On the Changing of the Weather”).
Treatise on the Judgement of Eclipses.
Treatise on the Dominion of the Arabs and its Duration (used to predict the end of Arab rule).
The Choices of Days (on elections).
On the Revolutions of the Years (on mundane astrology and natal revolutions).
De Signis Astronomiae Applicitis as Mediciam ‘On the Signs of Astronomy as applied to Medicine’
Treatise on the Spirituality of the Planets.
Two major theories of optics
appear in the writings of al-Kindi; Aristotelian
. Aristotle had believed that in order for the eye to perceive an object, both the eye and the object must be in contact with a transparent medium (such as air) that is filled with light. When these criteria are met, the “sensible form” of the object is transmitted through the medium to the eye. On the other hand, Euclid proposed that vision occurred in straight lines when “rays” from the eye reached an illuminated object and were reflected back. As with his theories on Astrology, the dichotomy of contact and distance is present in al-Kindi’s writings on this subject as well.
The factor which al-Kindi relied upon to determine which of these theories was most correct was how adequately each one explained the experience of seeing. For example, Aristotle’s theory was unable to account for why the angle at which an individual sees an object affects his perception of it. For example, why a circle viewed from the side will appear as a line. According to Aristotle, the complete
sensible form of a circle should be transmitted to the eye and it should appear as a circle. On the other hand, Euclidian optics provided a geometric model that was able to account for this, as well as the length of shadows and reflections in mirrors, because Euclid believed that the visual “rays” could only travel in straight lines (something which is commonly accepted in modern science). For this reason, al-Kindi considered the latter preponderant.
Through the Latin version of the De Aspectibus, Al-Kindi partly influenced the optical investigations of Robert Grosseteste
There are more than thirty treatises attributed to al-Kindi in the field of medicine
, in which he was chiefly influenced by the ideas of Galen
His most important work in this field is probably De Gradibus
, in which he demonstrates the application of mathematics to medicine, particularly in the field of pharmacology. For example, he developed a mathematical scale to quantify the strength of drug and a system, based the phases of the moon, that would allow a doctor to determine in advance the most critical days of a patient’s illness.
As an advanced chemist
, he was also an opponent of alchemy
; he debunked the myth that simple, base metals
could be transformed into precious metals such as gold
He is sometimes credited as one of the first distillers of alcohol
Al-Kindi authored works on a number of important mathematical subjects, including arithmetic, geometry, the Indian numbers, the harmony of numbers, lines and multiplication with numbers, relative quantities, measuring proportion and time, and numerical procedures and cancellation.
He also wrote four volumes, On the Use of the Indian Numerals
(Ketab fi Isti’mal al-‘Adad al-Hindi) which contributed greatly to diffusion of the Indian system of numeration in the Middle-East and the West. In geometry, among other works, he wrote on the theory of parallels. Also related to geometry were two works on optics. One of the ways in which he made use of mathematics as a philosopher was to attempt to disprove the eternity of the world by demonstrating that actual infinity
is a mathematical and logical absurdity.