Ancient Philosophical Visual Theories and their Use by Al-Fārābī

In the 10th century Baghdad, al-Fārābī in The Harmonization of the Opinions of the Two Sages: Plato the Divine and Aristotle (Kitāb al-ğamʿ bayna raʾyay al-ḥakīmayn Aflāṭūn al-ilāhī wa Arisṭāṭālīs), henceforth Harmonization, faces the problem of the unity of Greek philosophy against the opposition highlighted by the intellectuals of his time between Plato and Aristotle. Al-Fārābī discusses the agreement between Plato and Aristotle on crucial philosophical topics that, starting from al-Kindī, the Arab-Muslim philosophers had engaged from the origins of the falsafa: the question of the Creation of the world or its Eternity, the question of the Soul and Intellect and other crucial themes of logic, politics and ethics. In the course of this examination, al-Fārābī, quite unexpectedly, undertakes at length to discuss an apparently much more precise yet less significant question than those mentioned above, namely the alleged incompatibility between Aristotle’s theory of vision and that of Plato. The problem of vision was a theme researched in various disciplines: in the study of psychology and gnoseology philosophers had always reserved a privileged role for the sense of sight, the most difficult to explain among the perceptive faculties of man; physicians treated it in the study of anatomy, physiology and pathology of the eye, and through the birth of a specialty of the medical art such as ophthalmology. Astronomers sought to produce mathematical models for the representation of the perception of space driven by the constant attempt to make their observations of the vault of heaven more accurate. As Pines and Lindberg have shown – even if they did not pause to investigate the Farabian contribution in detail –, at the time of al-Fārābī there was a strong debate between the supporters of an extramission theory of vision on the model of the Platonic, Euclidean, Galenic and Kindian thought, according to which vision is caused by rays emitted by the eyes and the supporters of the immissive vision theory, of Aristotelian matrix, for which visual rays do not exist and it would be light to cause vision. Al-Fārābī probably counts among the latter Abū Bakr al-Rāzī (the Rhazes of the Latins), an older contemporary of his who had harshly criticized in two of his writings the extramission theory of vision, formulated by Galen and re-proposed by Ḥunayn ibn Isḥāq to Arab scientists, physicians and philosophers. These two controversial works are lost to us but can be partly reconstructed both from the testimony of Ibn Abī Uṣaybiʿa and from other writings of Abū Bakr al-Rāzī. This lively debate would explain the breadth of the discussion that al-Fārābī devotes to this topic in the Harmonization and would also explain the fact that al-Fārābī tackles the problem in some of his main works such as the Enumeration of Sciences (Iḥṣāʾ al-ʿUlūm), the Political Regime (al-Siyāsa al-madaniyya), the Epistle on Intellect (Risāla fī l-ʿaql) and the treatise On the Principles of the Opinions of the Inhabitants of the Virtuous City (Mabādi ʿārāʾ ahl al-madīna al-fāḍila). My paper focuses on the Farabian contribution to this debate. The strong impression is that the concordist proposal presented in Harmonization is the solution that al-Fārābī continues to adopt even in his main original treatises: the Aristotelian theory must be corrected in the Platonic sense regarding the passivity of the eye and of the faculty of the sight in the visual process. The corrections in the Platonic sense of the Aristotelian theory are, as we shall see, functional to the exquisitely gnoseological and psychological context of the theory of the intellect in which al-Fārābī introduces his own theory of vision. The study of the Farabian contribution to the theme of vision, compared to the results achieved by the Arab Hellenizers that preceded the Farabian speculation, is essential in understanding the thought of the generation of scholars following al-Fārābī: how much do Ibn Sīnā and Ibn Hayṯam owe to al-Fārābī? Ibn Hayṯam, indeed, as it is well known, is responsible for a theory of vision which is intromissive, yet original, and which consistently includes the physical doctrines concerning the Euclidean and Ptolemaic mathematical explanation of the visual process privileged in the previous Arabic tradition by al-Kindī, the anatomy and physiology of the eye analyzed in detail by Ḥunayn ibn Isḥāq and finally the Aristotelian doctrine on the propagation of light re-proposed by Ibn Sīnā, a contemporary of Ibn Hayṯam. We therefore come to what al-Fārābī writes regarding the theory of vision in Harmonization, in the Enumeration of Sciences, in the Political Regime, in the Epistle on Intellect and in the Principles of the Opinions of the Inhabitants of the Virtuous City.