The true light, which gives light to everyone
by Ken Myers
“In outlining the major shifts in the practice of natural philosophy which contributed to the rise of modern science, one might point to two developments as being of particular importance: the increased use of experiment, namely the contrived observation of nature rather than mere Aristotelian empeiria; and the wider deployment and increasing sophistication of mathematics. Is it possible to find any traces of such practices in the mediaeval schools? It has been argued that in the work of two Oxford Franciscans, Robert Grosseteste (c. 1170–1253) and Roger Bacon (c. 1220–c. 1292), one finds both the practice of experimental observation (the experimentum or scientia experimentalis) in the confirmation and falsification of hypotheses, and the more ready use of mathematical analysis. This distinguishes their approach from the various Aristotelianisms of the later middle ages and suggests that modern natural science may have identifiable origins prior to the Oxford Calculators or nominalists of the fourteenth century, and long before Kepler, Galileo or Newton.
“From where does this emphasis on mathematics and the experimentum emerge? It has its conceptual origins in the Neoplatonic image of light as a ‘formative power and form’ of nature and a means of knowledge by illumination. This Hellenistic tradition is the source of vivid light imagery deployed throughout early mediaeval Christian, Muslim and Jewish theology, for example in the works of St. Augustine, St. Basil, alFarabi, Avicenna and Avicebron. With scriptural precedent, light is associated with the life of God, emanation from divine being in the act of creation and the form of truth. Given that Grosseteste and Bacon were steeped in this tradition, particularly through the works of St. Augustine and the mystical theology of the Franciscans, it is unsurprising to find light as a central and unifying theme in their writings on natural philosophy, metaphysics and theology. An emphasis on the nature and meaning of light forges a bond between observation, natural philosophy, mathematics, metaphysics and theology for a number of reasons. Initially, four of these merit particular mention. First, light was implicated in many of the most fascinating and mysterious natural phenomena: the rainbow, the halo surrounding the atmosphere and light’s presence in the uncorrupted and perfectly moving celestial bodies. Secondly, it is light itself which is the form of truth and which makes all things both visible and knowable. Thus observation, the experimentum, is intimately linked to the attainment of truth through the mediation of light, both spiritual and visible. Thirdly, through a long tradition of investigation into the behaviour of light (perspectiva), exemplified in the works of Euclid and Ptolemy’s treatises on optics, it was known that visible light acts according to the strict patterns of a yet more real and abstract mathematical geometry. In true Platonic fashion, mathematics could then mediate between the Supreme Light or Highest Truth, and the weaker light reflected in created nature which is nevertheless an emanation from that Highest Truth. At the beginning of his treatise De Lineis, Angulis, et Figuris, Grosseteste writes a much quoted exhortation to the use of mathematics in natural philosophy: “The usefulness of considering lines, angles and figures is the greatest, because it is impossible to understand natural philosophy without these.” Finally, and perhaps most importantly, the Christian scriptures describe God as light, and Christ as the light of the world. On these grounds writers such as the Pseudo-Dionysius understood God to be the uncreated Light, and visible light to be God in action. For Grosseteste, and later Bacon, to study light was to study God and all things in relation to God.”
— from Simon Oliver, ”Robert Grosseteste on Light, Truth and Experimentum” (Vivarium 42,2; available online at brill.com)