Al-Kindi's De Radiis: The Theory of Rays and Astral Magic

De radiis ("On the Rays"), also called Theorica artium magicarum ("The Theory of the Magic Arts"), is a short treatise attributed to the ninth-century Arab philosopher al-Kindi that explains magic as a natural effect of rays emitted by the stars and by every thing in the world. It argues that the heavens determine all events through a web of radiation, and that human words, images and intentions also send out rays that can act on matter. Surviving only in Latin, it became the most coherent philosophical theory of magic available to medieval Europe and shaped the astral magic of the Renaissance.

Al-Kindi, the Philosopher of the Arabs§

Abu Yusuf Ya'qub ibn Ishaq al-Kindi was born around 800 into a noble family of the Arab tribe of Kinda, whose members had governed Kufa. He studied in Basra and Baghdad and became a scholar at the court of the caliphs al-Ma'mun and al-Mu'tasim, serving as tutor to the latter's son. Later generations called him "the philosopher of the Arabs", because he was the first major thinker of Arab descent to write philosophy in Arabic.

His output was enormous. The bibliographer Ibn al-Nadim lists more than two hundred titles on metaphysics, ethics, mathematics, music, medicine, astronomy, astrology, optics, meteorology and cryptography. Al-Kindi also led a circle of translators who rendered Greek philosophy into Arabic. Among their productions were the so-called Theology of Aristotle, actually a paraphrase of parts of Plotinus' Enneads, and material drawn from Proclus that later became the Book of Causes. Through this circle Neoplatonic ideas of emanation and cosmic hierarchy entered Arabic thought.

Al-Kindi was not a magician. He was a philosopher and scientist who sought to explain the natural world by universal causes, and his interest in astrology, optics and the action of bodies at a distance led him to a theory of rays that also covered the phenomena his contemporaries called magic.

The Latin Text and Its Authorship§

No Arabic manuscript of De radiis is known. The work circulated in Latin from at least the thirteenth century, under al-Kindi's Latin name Alkindus, and its translator and date of translation are unknown. The standard critical edition was published in 1974 by Marie-Thérèse d'Alverny and Françoise Hudry.

Because the original is lost, some scholars have doubted the attribution. Most specialists, however, consider it either al-Kindi's own work or closely dependent on his teaching: its doctrine of rays matches his authentic writings on optics and astrology, and its style of argument, building a universal principle and then applying it to particular cases, is characteristic of him. Pinella Travaglia's study of 1999 and Peter Adamson's survey of al-Kindi's thought both treat it as a genuine expression of his natural philosophy.

The treatise is divided into short chapters. It begins with the rays of the stars, extends the theory to the elements and all composite things, and then applies it in turn to the power of words, to figures and characters, to images and to sacrifices. Its tone is that of a philosophical demonstration rather than a book of recipes.

Celestial Harmony and the Rays of the Stars§

The treatise opens with astrology. The heavenly bodies, al-Kindi argues, act on the world below by means of rays. Each star has its own nature, and the effect of its rays depends on its position, its relation to other stars and the place where the rays fall. Because the stars are constantly moving, the configuration of rays is never the same twice, and this explains the endless variety of things and events in the sublunary world.

From this follows a strong claim. The whole "harmony" of the heavens at any moment determines the condition of everything below. Someone who fully understood the celestial harmony would therefore know the state of every thing in the world, past, present and future, because each thing is, in a sense, an image of the heavenly configuration in which it came to be. No human being achieves this knowledge, but the astrologer approximates it by studying the principal configurations.

This is a thoroughly determinist cosmology. It also implies a doctrine of correspondences: the world of the elements is an image of the celestial world, and every individual thing contains, in its own way, the condition of the whole. The idea echoes Neoplatonic sympathy (see Correspondences) but is formulated in terms of physical causation.

Every Thing Radiates: The Theory Extended to the Elements§

Al-Kindi's boldest step is to generalise the doctrine. It is not only the stars that emit rays. Everything that actually exists in the world of the elements, whether a stone, a plant, an animal or a fire, emits rays in every direction, according to its own nature. These rays fill the world, so that every thing acts in some way on every other thing, and is acted on in turn.

The theory draws on al-Kindi's optics. In his work on vision, known in Latin as De aspectibus, he argued that light and visual rays travel in straight lines from every point of a luminous or seeing body, in all directions, and he treated radiation as a universal mode of causal action. De radiis turns this optical model into a general physics: the cosmos is a network of rays crossing in all directions, and causation is the transmission of power along them.

The result is a natural explanation for phenomena that might otherwise seem marvellous. Fire heats at a distance, a magnet attracts iron, a medicine acts on the body and a star shapes the seasons by the same principle. Nothing in nature is inert, and the differences between the effects of things depend on the strength and nature of their rays and on the disposition of what receives them.

Words, Figures and Images: A Natural Theory of Magic§

The later chapters apply the theory to the practices of magic. Human beings, al-Kindi argues, also emit rays, and their imagination plays a special role. When a person conceives an image of a thing in the imagination with strong desire and intention, that mental image itself becomes a source of rays that can act on external matter, especially when the person's faith is firm and the astrological moment is favourable.

Spoken words work in the same way. A voice produced with intention and imagination emits rays that move the air and through it act on things, and certain words, uttered at a suitable time, have greater power than others. Al-Kindi uses this to explain the efficacy of prayers and invocations naturally, as the joint effect of the speaker's imagination, the words and the celestial situation. Figures and characters drawn or engraved with intent, and images (talismans) made of suitable materials under chosen stars, act likewise. Even sacrifices are explained by the rays of the victim, the offerer and the moment, an analysis that is philosophical rather than practical.

This argument made magic, in principle, a branch of natural philosophy. It did not depend on demons or spirits at all, but on the radiation of natural powers, amplified by the soul's imagination. That is what made the treatise so attractive to later thinkers who wished to defend a "natural" or "spiritual" magic against the charge of demonic collusion (see Natural Magic). In the same period, the Harranian scholar Thabit ibn Qurra wrote on talismanic images in a similar astrological framework (see Sabians of Harran), and the later Arabic Picatrix combined a comparable theory with detailed planetary rituals.

Influence and Condemnation in Latin Europe§

In Latin Europe De radiis was read alongside the optical works of al-Kindi and of Ibn al-Haytham (Alhazen). Robert Grosseteste's philosophy of light and Roger Bacon's doctrine of the "multiplication of species", according to which every natural agent radiates its likeness in all directions, are closely related to its central idea, and Bacon cited al-Kindi as an authority on rays. The doctrine helped to give medieval natural philosophy a vocabulary for action at a distance.

Theologians were more alarmed. In his Errores philosophorum (usually dated around 1270) the Augustinian theologian Giles of Rome devoted a chapter to the errors of al-Kindi, objecting to his astral determinism and to the claim that words, figures and sacrifices have natural power. The debates over image magic in the thirteenth century, reflected in the Speculum astronomiae and in the Paris condemnation of 1277, formed the background to this criticism.

In the Renaissance the theory found new readers. Marsilio Ficino's Three Books on Life (1489) explained the action of the heavens through rays and spirit and discussed the power of images, songs and words in terms that recall al-Kindi, and Giordano Bruno's writings on "bonds" developed a theory of influence through imagination with a similar structure. Historians such as D. P. Walker have treated al-Kindi as one of the main medieval sources of this "spiritual magic". Today De radiis is studied as a landmark attempt to give magic a rational, physical foundation.

Frequently asked questions§

What is De radiis about?§

De radiis argues that the stars and every existing thing emit rays that act on all other things. It uses this theory to explain astrology and then the power of words, figures, images and sacrifices as natural effects, made stronger by human imagination and intention.

Did al-Kindi write De radiis?§

The treatise survives only in Latin and its Arabic original is lost, so its authorship cannot be proven. Most scholars accept it as al-Kindi's work or as a faithful expression of his ideas, because it matches his authentic writings on optics and astrology.

Why was De radiis considered dangerous?§

Medieval theologians such as Giles of Rome objected to its astral determinism, which seemed to leave no room for free will, and to its claim that words and images have natural power. They feared it gave philosophical cover to magical practices.

Sources and further reading§

• Al-Kindi — Peter Adamson, 2007
• The Philosophical Works of al-Kindi — Peter Adamson & Peter E. Pormann (trans.), 2012
• Magic, Causality and Intentionality: The Doctrine of Rays in al-Kindi — Pinella Travaglia, 1999
• Theories of Vision from al-Kindi to Kepler — David C. Lindberg, 1976
• Spiritual and Demonic Magic from Ficino to Campanella — D. P. Walker, 1958
• Magic in the Middle Ages — Richard Kieckhefer, 1989
• Les 'images astrologiques' au Moyen Âge et à la Renaissance — Nicolas Weill-Parot, 2002