Ruth Glasner presents an illuminating reappraisal of Averroes' physics. Glasner is the first scholar to base her interpretation on the full range of Averroes' writings, including texts that are extant only in Hebrew manuscripts and have not been hitherto studied. She reveals that Averroes changed his interpretation of the basic notions of physics - the structure of corporeal reality and the definition of motion - more than once. After many hesitations he offers a bold new interpretation of physics which Glasner calls 'Aristotelian atomism'. Ideas that are usually ascribed to scholastic scholars, and others that were traced back to Averroes but only in a very general form, are shown not only to have originated with him, but to have been fully developed by him into a comprehensive and systematic physical system. Unlike earlier Greek or Muslim atomistic systems, Averroes' Aristotelian atomism endeavours to be fully scientific, by Aristotelian standards, and still to provide a basis for an indeterministic natural philosophy. Commonly known as 'the commentator' and usually considered to be a faithful follower of Aristotle, Averroes is revealed in his commentaries on the Physics to be an original and sophisticated philosopher.

This volume offers a new English translation, introduction, and detailed commentary on Sefer Meyasher 'Aqov, (The Rectifying of the Curved), a 14th-century Hebrew treatise on the foundation of geometry. The book is a mixture of two genres: philosophical discussion and formal, Euclidean-type geometrical writing. A central issue is the use of motion and superposition in geometry, which is analyzed in depth through dialog with earlier Arab mathematicians. The author, Alfonso, was identified by Gita Gluskina (the editor of the 1983 Russian edition) as Alfonso of Valladolid, the converted Jew Abner of Burgos. Alfonso lived in Castile, rather far from the leading cultural centers of his time, but nonetheless at the crossroad of three cultures. He was raised in the Jewish tradition and like many Sephardic Jewish intellectuals was versed in Greek-Arabic philosophy and science. He also had connections with some Christian nobles and towards the end of his life converted to Christianity. Driven by his ambition to solve the problem of the quadrature of the circle, as well as other open geometrical problems, Alfonso acquired surprisingly wide knowledge and became familiar with several episodes in Greek and Arabic geometry that historians usually consider not to have been known in the West in the fourteenth century. Sefer Meyasher 'Aqov reflects his wide and deep erudition in mathematics and philosophy, and provides new evidence on cultural transmission around the Mediterranean.

Gersonides was a highly original Jewish philosopher, scientist and biblical exegete, active in Provence in the first half of the fourteenth century. Ruth Glasner explores his impressive achievements, and argues that the key to understanding his originality is his perspective as an applied mathematical scientist. It was this perspective that led him to examine Aristotelianism from directions different from those usually adopted by contemporary scholastic scholars. Gersonides started on his way, as he himself claims, as a 'mathematician, natural scientist, and philosopher', who believed in his power to solve the main problems of medieval science. He ended up concentrating on his work as a mathematical astronomer, developing techniques of observation and computation, and somewhat less optimistic about the prospect of scientific knowledge.