Abu’l-Walid Muhammad bin Ahmad Ibn Rushd, ابن رشد, (Latinized name: Averroes) was born in Córdoba (Spain) to a family with a long and respected tradition of legal and public service in 1126. His father Abu al-Qasim was the chief judge of Córdoba [1]. Ibn Rushd died in Marrakech (Morocco) in the year 1198 AD, and his body was returned to Córdoba for burial [2].
His works range from philosophy, astronomy, and medicine to religion. He would be the most influential of Aristotle’s medieval commentators, writing comments and corrections on all the Aristotelian works available to him [3]. Scholars in Christian Europe would refer to him as “the Commentator [of Aristotle].” The revival of Aristotelism in twelfth-century Europe was mainly based on Ibn Rushd’s commentaries. However, in the Islamic world, Ibn Rushd’s defense of rationalist philosophy would be less influential than the religious Asharite philosophy that emphasized divine manifestations in nature, as advocated by al-Ghazali (al-Ghazel) الغزالی.
Ibn Rushd tried to formulate a theory of light and color, as consistent with Aristotle and his followers as possible. Like Ibn Sina had done previously, Ibn Rushd provided many arguments why the so-called extramission theories from Ptolemy and Euclid were absurd, and vision cannot be caused by visual rays emerging from the eye. Similar to Ibn Sina, Ibn Rushd explained vision in terms of forms transmitted from the visible object to the eye, i.e., an intromission theory [4].
Ibn Rushd maintained that colors exist even when they are not perceived, and that light is necessary for colors to be visible [5]. In a manner similar to Ibn al-Haytham’s approach, Ibn Rushd considered light as playing an active role in color vision, thus breaking with the traditional Aristotelian view. However, unlike Ibn al-Haytham, Ibn Rushd did agree with Aristotle that the medium also played an active role in color vision. Apparently, Ibn Rushd was not aware of the theory on the vision that had been proposed by Ibn al-Haytham, successfully combining the various classical theories into one mathematical–physical intromission theory of light, color, and vision.
10.1 Ibn Rushd’s Color Theory
Ibn Rushd explained the different species of color as consisting of various mixtures of bodies of much or little transparency with bodies of much or little luminosity. Since every material is composed of the four elements, with only water and air being transparent and only fire being luminous, the color of a material can be attributed to the relative amounts of the elements. This explanation was later adopted by Theodoric of Freiberg (p. 172 of Ref. [6]), who explained it in terms of four principles (much or little transparency, much or little luminosity) of colors.
Ibn Rushd did not agree with Ibn Sina’s criticism of the Aristotelian ideas on color mixing. In his Jawāmi’ al-āthār al-‘ulwiyya,
, (Short Commentary on the Meteorology: 74, 19–76, 18), Ibn Rushd defended the Aristotelian view by arguing that it referred to color mixing in a qualitative sense, but not in a quantitative sense [7, 8]. For example, Ibn Rushd argued that green is formed by mixing the yellow that exists in light red with the black that is in purple. From a modern point of view, this makes the approach philosophical rather than scientific. In addition, in his description of the rainbow, Ibn Rushd closely followed Aristotle: The rainbow forms by the reflection of sunlight on individual raindrops that reflect light and transmit color [6].
Ibn Rushd’s ideas on color would be influential on later scholars. In his works on colors (De coloribus) and on the rainbow (De iride), Theodoric of Freiberg (d. 1318) makes clear that his theory on the formation of colors is based on Ibn Rushd’s color theory (p. 47 of Ref. [9]; p.11 of [10]). Theodoric literally quotes the Latin translation of Ibn Rushd’s Tractato de Sensu et Sensato (p. 35n2 of Ref. [9]) [11]. His description of the colors of the rainbow and also his four principles by which color is explained were all explicitly taken from Ibn Rushd’s work.
Stamp commemorating Ibn Rushd from Tunisia. (Image obtained from public domain)