THE CONTINGENCY ANGLE: AN PHILOSOPHICAL ISSUE IN MATHEMATICS

From Euclid to the second half of the 17th century, mathematicians as well as philosophers continued to raise the question of the angle of contact and, generally, of the concept of angle. This article is the first essay devoted to this subject in Arabic mathematics. It deals with Greek writings translated into Arabic on the one hand, and contributions of Arabic mathematicians on the other hand: al-Nayrizi, Ibn al-Haytham, al-Samaw'al, al-Shirazi, al-Farisi, al-Qushji, among others. Most of these contributions are hitherto unknown.