The notion of light has greatly influenced centuries of philosophical speculation and led to metaphysical, cosmological, and noetic theories. In the mythologies of early cultures and religions, light was conceived as an important condition not only of life but also of sight and knowledge. Although usually connected with the divine, in many religions light was not so much a constituent as an attribute of the deity–a life-giving factor, a cause of happiness, wealth, health, knowledge, and beauty. Dualistic religions held that light (in man the pneuma or spirit or soul), after separation from the deity, was chained to matter; through purification, however, it could return to its origin.
Greek Thought. Philosophers rationalized the notion of light. In Greek thought, Heraclitus’s theory of fire as the first principle of the world initiated an ontology of light that was further developed by the Stoics and the Pythagoreans into a dualism of light and darkness. Parmenides assigned this theory to the realm of opinion. Light, he held, is as little related to darkness as being is related to nonbeing.
The nucleus of Plato’s teaching is the Good; this enlightens the intelligible world just as the sun illumines the sensible world. Thus, for him, the perfect Idea of the Good becomes at once the principle of being and knowing.
Aristotle held that the cosmos consists of five elements: earth, water, air, fire, and ether. He considered ether the finest of all elements, filling the highest spheres of the cosmos and constituting the celestial bodies. Ether, in his view, is not mixed with heterogeneous particles; its purity accounts for the circular (that is, perfect) movement of the heavens in contrast with the less perfect up and down motion of the other elements. During the Middle Ages it was called the quinta essentia, light, the clarity of the heavenly regions.
Neoplatonism. Neoplatonic systems are rich in speculations concerning light. In Philo’s teaching, Plato’s Idea of the Good is not spoken of figuratively; it is the spiritual light. However, it was Plotinus who first developed a metaphysics of light, considering light no longer as a physical substance. From the One emanates immaterial light, radiating outward, growing dimmer and dimmer until it shades off into darkness (a privation of light), which is matter. From the One also proceeds Nous (thought, mind), which knows all things simultaneously in an eternal now. From Nous emanates the world soul; from the latter emanate human souls and finally material beings. They do not lack light completely, for they are illumined by form, which is considered the exteriorization of the intelligible. Here light starts its ecstatic return to its origin and proves that the sensible and the intelligible are bound together. Such unity allows for mystical and prophetical experience and knowledge.
Medieval Development. Augustine combined the teaching of Neoplatonism and Plato’s Idea of the Good with revealed truths. For instance, he applied Genesis 1.3 (‘‘Let light be made”) to the creation of the mundus intelligibilis, the world of the angels. He accepted the Platonic distinction between sensible and spiritual light. Like Plato, Augustine cautioned men not to trust the sensible realm. Christ is called “Light” in the sense that He enlightens every man, although man is free to turn toward or away from the Light. On such ontological premises Augustine built his theory of illumination, which had considerable impact on medieval thought.
Pseudo-Dionysius. The Hierarchia caelestia of Pseudo-Dionysius became the handbook of Christian symbolism. From God, the Father of Lights, comes all radiation. The physical light that attracts bodily beings symbolizes the divine immanence and transcendence, for it penetrates all things while remaining pure itself. Light is also the forming power within man, leading him upward and uniting him to the Father of Lights.
Arabs and Jews. In later centuries an amalgamation of Christian, Jewish, and Arabian thought led to a fuller development of the metaphysics of light. Some Arabian and Jewish philosophers saw light as a substance or a power. The literature of the Talmud and Midrash speaks of light as the garment of God: God took His garment and spread it like a mantle, thus creating the celestial world. Isaac Israeli taught that, in the hierarchy of being, the lower beings proceed from the shadow of the higher, for example, from the shadow of Intelligence originates the anima rationalis, from its shadow, the anima bestialis, and so on. Through a good moral life man participates in the light of the Intelligence. Similar doctrines were held by the Arabs, mainly by Alfarabi, Avicenna, and Algazel, who combined Aristotelian, Neoplatonic, and Oriental thought.
Grosseteste. Influenced by thinkers of his era, Robert Grosseteste formed an elaborate metaphysics of light. God is the Eternal Light and Exemplary Form of all things. He first created forma prima and materia prima. Forma prima is a point of light that by its very nature diffuses itself and becomes the corporeal form of matter. In this process materia prima is expanded into the three spatial dimensions of the finite universe. As corporeal form, light functions as a principle of distinction and multiplicity and continuity in nature. “All things are one by the perfection of one light.” The rarefaction of matter through light is considered the highest actualization of matter; it is exemplified by the firmament, “the first body,” which has nothing “in its composition but first matter and first form.” Through this expansion of matter by light, nine celestial immutable spheres are built. The innermost of these concentric spheres is the sphere of the moon, which produces through its own light the four infralunar spheres consisting of fire, air, water, and earth. The infralunar regions are subject to change and corruption. Their beings are determined, specified, and perfected by light; and here light becomes also the principle of motion and color. Light gives these bodies form, actuality movement, and color.
As a consequence of this speculation, optics came to be greatly developed. In its service stood geometry, the study of light diffused from a central point into straight lines, reflected and refracted by angles, and providing a mathematical structure for the universe. Grosseteste’s theory had decisive intfuence upon the natural philosophers at Oxford (Adam Marsh and Roger Bacon) and at Paris (Alexander of Hales, Bonaventure, and others). Grosseteste’s clear distinction between corporeal and noncorporeal light no longer prevailed in the De lntelligentiis of Adam Pulchrae Mulieris, who returned to a light-monism: “Unumquodque quantum habet de luce, tantum retinet esse divini.” Unlike these thinkers, St. Thomas Aquinas did not accept light as substantial form but understood it as a quality and applied it by analogy to the intelligible realm.
Renaissance and Modern Thought. During the Renaissance a revival of the metaphysics of light occurred in the theories of such philosophers as M. Ficino, G. Bruno, and J. Böhme. G. Pico della Mirandola, who combined Neoplatonism, medieval Christian theology, and Cabala, spoke of the supernatural light (faith), the natural light, and the light of glory. Man, a microcosm, contains in himself the cosmic sources of light and possesses also the light of the agent intellect.
Francesco Patrici da Cherzo (1529-97) returned to a Neoplatonic doctrine of light in which God is the original, uncreated Light. From Him light emanates as a metaphysical principle of being, causing multiplicity and life as well as the unity of beings. Light is a kind of an intermediary between the purely spiritual and the purely material. Besides light, there are other factors in nature, namely, warmth, space, and fluidity.
Little philosophical work has been done on later theories of light. The scientific current leads to physicomathematical theories, as in Newton’s Opticks (1704), rather than to metaphysical analysis. Newton postulated an ethereal medium mainly to account for the propagation of light, which he could not explain in purely mechanical terms. Light was conceived and spoken of merely in the sensible realm by G. Berkeley and the British empiricists, whereas F.H. Jacobi applied the term to a supersensible reality open only to intuition. However, contemporary work in the philosophy of science, particularly that associated with interpretations of quantum theory, is more and more directed to investigating the reality that lies behind the physicist’s equations.
From: “Light, Metaphysics of” New Catholic Encyclopedia, 2nd ed. vol. 8 (Detroit: Gale, 2003), pp. 583-584. ©2013 Catholic University of America, publishing rights held by Gale, a part of Cengage Learning, Inc. Reproduced by permission.