Al-Kindi

Abu Yusuf Yaqub ibn Ishaq al-Kindi was an Arab philosopher and scientist who worked in Baghdad in the ninth century. Often called the first philosopher of the Islamic world and "the philosopher of the Arabs", he was the first major thinker to write philosophy in Arabic, drawing on newly translated Greek texts to argue that reason and Islamic revelation agree. He also wrote on mathematics, astronomy, optics, music, medicine and cryptography, and his method for breaking codes is the earliest known description of frequency analysis.

Al-Kindi was born around 800, probably in Kufa in southern Iraq, though some sources name Basra. He came from the Kinda, a noble Arab tribe of southern Arabia, which is why later writers stressed that he was an Arab by descent, unusual among the scholars of his day. His father is said to have been governor of Kufa. He studied in Basra and then in Baghdad, capital of the Abbasid Caliphate.

He rose under the caliphs al-Mamun (813 to 833) and al-Mutasim (833 to 842), at the height of the movement that translated Greek philosophy and science into Arabic. Al-Kindi was associated with the House of Wisdom, the scholarly centre linked to the caliphal court, alongside figures such as the mathematician Al-Khwarizmi. He tutored al-Mutasim's son Ahmad and dedicated his best-known philosophical work to the caliph.

His fortunes fell under al-Mutawakkil (847 to 861). Accounts say that rivals at court, the Banu Musa brothers, turned the caliph against him; he was beaten and his library confiscated for a time, though it was later returned. He died in Baghdad around 870, perhaps in 873, reportedly a lonely man.

Al-Kindi did not translate Greek himself as far as is known, but he gathered and directed a circle of translators, many of them Christians who knew Greek and Syriac. Works produced in this circle included Arabic versions of parts of Aristotle's Metaphysics and the so-called Theology of Aristotle, which was in fact a reworking of parts of Plotinus's Enneads. The confusion meant that Neoplatonic ideas entered Islamic thought under Aristotle's name, and al-Kindi's own philosophy blended the two traditions.

He saw his task as making Greek wisdom available to an Arabic-speaking public and showing that it was compatible with Islam. In the preface to On First Philosophy he argued that truth should be welcomed wherever it comes from, even from foreign peoples, a direct answer to critics who distrusted the "foreign sciences".

On First Philosophy deals with metaphysics, which al-Kindi defined as knowledge of the first truth, the cause of all truth. Its most original argument concerns the creation of the world. Most Greek philosophers, Aristotle included, held that the world is eternal. Al-Kindi, siding with the Quranic doctrine of creation, argued that an actually infinite quantity, body or time is impossible, so the universe must have had a beginning and must have been brought into being from nothing by God. This line of reasoning was later taken up by Muslim theologians and, through them, by Christian and Jewish thinkers.

He described God as the "True One", absolutely simple, beyond all description, and the source of unity in everything else, since every created thing is in some sense both one and many. This emphasis on God's utter unity echoed both Neoplatonism and the concerns of the Mutazilite theologians of his time, though how closely he was linked to them is debated.

In psychology he followed the Greek view that the soul is a simple, immortal substance distinct from the body. His short Epistle on the Intellect classified kinds of intellect in a scheme that later Islamic philosophers developed. His popular treatise On the Means of Dispelling Sorrows offered Stoic-style advice: since worldly goods can always be lost, a wise person attaches their happiness only to things of the mind.

Al-Kindi believed that mathematics was the necessary foundation of philosophy. He wrote on arithmetic, geometry and astronomy and helped introduce Indian numerals to the Arabic-speaking world, alongside al-Khwarizmi. In optics he criticised the theory that vision depends on forms travelling from the object into the eye, defending instead a geometrical theory of rays coming from the eye, a work later read in Latin as De aspectibus. He wrote on the mathematics of music, on pharmacology, where he tried to quantify the strength of compound drugs, and on astrology, meteorology, perfumes, swords and much else.

His treatise on deciphering encrypted messages explained how to break a substitution cipher by counting how often each letter appears in a text and comparing this with the normal frequencies of letters in the language. It is the first known account of this technique, the basis of cryptanalysis for centuries.

The tenth-century bibliographer Ibn al-Nadim listed about 260 works by al-Kindi, most of them short treatises. Only a fraction survives, some only in Latin translation. His philosophical style was soon overtaken by more systematic Aristotelians, above all Al-Farabi and later Avicenna, whose works largely replaced his. His students, notably Ahmad ibn al-Tayyib al-Sarakhsi and Abu Zayd al-Balkhi, carried on his approach for a generation.

In medieval Europe, several of his scientific and philosophical works were translated into Latin in the twelfth century, partly by Gerard of Cremona, and he was read under the name Alkindus. The Renaissance mathematician Girolamo Cardano counted him among the twelve greatest minds in history. Today he is remembered as the founder of Islamic philosophy and a leading figure of the Islamic Golden Age, whose career shows the intellectual life of Abbasid Baghdad at its height. For more on the land where he lived, see the History of Iraq.