In this article we study the development of the mathematical theorem, now known as the T Couple, and discuss the difference between its plane and spherical applications.

L'Abrégé de l'Almagested'Averroès, conservé uniquement en traduction hébraïque, reste inédit et peu étudié. Cet article a pour but de le faire connaître. Après avoir retracé l'histoire de l'Abrégé: date de rédaction, traduction, transmission de cette traduction, diffusion et audience, nous procédons à une première étude du texte: aperçu commenté du contenu, identification des sources et examen de leur exploitation critique par Averroès. Nous donnons également une traduction d'extraits significatifs du Prologue de l'Abrégé, avec une brève analyse. Avec l'Abrégé, nous disposons (...) d'un témoignage direct et relativement précoce, dû à l'un des plus importants artisans du mouvement de contestation et de réforme de l'astronomie ptoléméenne, animé au XIIe siécle par des penseurs andalous, philosophes aristotéliciens pour la plupart. (shrink)

In this article we study the development of the mathematical theorem, now known as the Tūsī Couple, and discuss the difference between its plane and spherical applications. Dans cet article, nous étudions le développement du théorème mathématique, connu maintenant sous le nom de ‘couple d'al-Tūsī’; et nous discutons la différence entre son application plane et son application sphérique.

The Earth is positioned at the center of the universe in the Ptolemaic model of the universe. The center of the Earth is at the same time the center of the universe in this model. This system, which was constructed according to Aristotelian physics, was accepted as the prevailing theory up to the adoption of the heliocentric universal model in the 16th century. The Earth was at the same time assumed to be completely stationary in the geocentric theory. Movement around (...) its own axis or around another celestial body was out of the question for it. In Antiquity and the Middle Ages when observational instruments like the telescope were not yet in use, this theory was seen to be rationally based on data obtained directly from the senses. In this context, various justifications had been provided about the world being stationary and existing at the center. Representatives from the Peripatetic philosophy in the Muslim world also were seen to accept the geocentric model. In The Book of Healing, Ibn Sīnā (d. 1038 CE) subjected the proofs that had come to him about the Earth being stationary by distinguishing an independent chapter. The 14th century follower of Ibn Sīnā’s philosophy, Najm al-Dīn al-Kātibī addressed this topic in Ḥikmat al-‘ain, and the work’s principle commentators also commented on his assessments. This study will address Ibn Sīnā’s assessments on the Earth being stationary in the geocentric model of the universe and will discuss the reflections of these assessments in Ḥikmat al-‘ain as an Avicennan text. (shrink)