Medieval Optics

by

Dallas G. Denery

• LAST REVIEWED: 15 January 2019
• LAST MODIFIED: 15 January 2019
• DOI: 10.1093/obo/9780195396584-0260

Introduction

Medieval optics, also known as perspectivist optics from the mid-13th century on, offered a complete theory of human cognition. Whereas modern optics limits itself to the study of the behavior and properties of light, perspectivist optics sought to explain how human beings perceive and then understand the world around them. The perspectivists contended that vision proceeds through a process of intromission, in other words, we see objects in the world because information from those objects, called “species,” reach and then reproduce themselves within the eye and then throughout the various faculties of human the brain. Prior to the 13th-century popularization of perspectivist optics, most European and Christian thinkers believed vision occurred through a process of extramission, in which vision depended on visual rays extending out from the eyes to the things in the world. Medieval optics derives largely from the work of Alhacen (b. c. 965–d. c. 1040), the 12th-century Arabic thinker. In The Book of Optics, translated into Latin in 1200 as De aspectibus, Alhacen (Ibn al-Haytham) wove together the mathematical and geometrical aspects of Ptolemy’s extramission account of vision, Galen’s physiological account of the eye, and ideas about light from such Arabic thinkers as Alkindi (b. c. 801–d. c. 873), to create a sophisticated intromissionist account of vision. The Franciscan Roger Bacon (b. c. 1219–d. c. 1292), working from the Latin translation, borrowed all of these ideas for his own treatise, Perspectiva, and combined them with Avicenna’s Aristotelian-influenced faculty psychology. If not terribly original, Bacon’s treatise, along with works by his fellow Franciscan John Pecham (b. c. 1230–d. c. 1292), and the Silesian cleric Witelo (b. c. 1230–d. c. 1300), proved tremendously influential. Perspectivist ideas filtered into scholastic debates about natural causation and physics, cognition, epistemology, the Eucharist, and, even, the beatific vision. Various religious and pastoral treatises bear the imprint of perspectivist ideas, as do works by such renowned medieval authors as Jean de Meun (b. c. 1240–d. c. 1305), Dante (b. c. 1265–d. c. 1321), and Chaucer (b. c. 1343–d. c. 1400). Perspectivist ideas may even have played a part in the development of illusionistic painting in Italy, beginning with Giotto’s early-14th-century frescos at the Arena Chapel in Padua and culminating with Alberti’s 1435 treatise, On Painting. It was only in the early 17th century, with the publication of Johannes Kepler’s Emendations to Witelo, that the tradition of medieval optics as a comprehensive account of human cognition came to an end. Kepler (b. 1571–d. 1630) reimagined the eye as a camera obscura with a lens to focus light on the retina, effectively separating the study of optics from the study of cognition. The modern science of optics was born.

General Overviews

Lindberg 1976 establishes medieval optics as a defined area of academic inquiry and remains an excellent introduction to the topic from its deep origins in the classical past until the 17th century. In many ways, the vibrant field of medieval visuality studies owes its origin to this book. Smith 2015 is a superb survey of optical theory that takes account of much recent work and offers convincing corrections to Lindberg, stressing especially the cognitive aspects of medieval optics. Beyond these two works, most overviews of the history of optics, such as Darrigol 2012, give little more than a passing glance at the medieval period, although they can be useful for setting up contrasts with the earlier and later periods. More useful in this regard is Clark 2007, which interprets the early modern culture of doubt and skepticism in light of tensions within perspectivist theory. Edgerton 2009 narrates the development of Renaissance linear perspective with roots in Bacon’s theories.

• Clark, Stuart. Vanities of the Eye: Vision in Early Modern European Culture. Oxford: Oxford University Press, 2007.

  Analyzes the impact that the potential skeptical consequences of medieval optics had on the early modern period.

• Darrigol, Olivier. A History of Optics from Greek Antiquity to the Nineteenth Century. Oxford: Oxford University Press, 2012.

  The only modern, scholarly survey that attempts to cover the entire history of the topic, although it focuses primarily on the aftermath of Kepler’s work.

• Edgerton, Samuel Y. The Mirror, the Window, and the Telescope: How Renaissance Linear Perspective Changed Our View of the Universe. Ithaca, NY: Cornell University Press, 2009.

  An accessible introduction to the impact of perspectivist optics on Renaissance art and culture.

• Lindberg, David C. Theories of Vision from Al-Kindi to Kepler. Chicago: University of Chicago Press, 1976.

  The book that established the academic study of medieval optics from its classical roots to Kepler. It remains essential.

• Simon, Gérard. Archeologie de la vision. Paris: Éditions de Seuil, 2002.

  Narrates a history of optical theory characterized by three great mutations: beginning with Euclid and Ptolemy, passing through Alhacen, and concluding with Kepler and Descartes.

• Smith, A. Mark. From Sight to Light: The Passage from Ancient to Modern Optics. Chicago: University of Chicago Press, 2015.

  An excellent history of the rise and fall of medieval optics with much attention paid to the classical tradition. By stressing the cognitive aspects of optical theory, Smith argues convincingly against Lindberg 1976 that Kepler marks the complete rejection of perspectivist optics.