Levi ben Gerson (1288–1344) was a medieval astronomer who responded in an unusual way to the Ptolemaic tradition. He significantly modified Ptolemy’s lunar and planetary theories, in part by appealing to physical reasoning. Moreover, he depended on his own observations, with instruments he invented, rather than on observations he found in literary sources. As a result of his close attention to the variation in apparent planetary sizes, a subject entirely absent from the Almagest, he discovered a new phenomenon of Mars (...) and noticed a serious flaw in Ptolemy’s treatment of the Moon. (shrink)

The ArgumentLevi ben Gerson, also known as Gersonides or Leo de Balneolis, was one of the most original Jewish thinkers of the Middle Ages, and he wrote on logic, philosophy, biblical exegesis, mathematics, and astronomy. During the last years of his life he maintained relations with the papal court of Clement VI (1342–52) at Avignon, and collaborated in the translation into Latin of hisSefer Tekhuna(Book of Astronomy). The object of this paper is to establish the main stages of the redaction (...) of the Hebrew and Latin extant versions of his astronomical work. Although Levi declares that the work was finished in 1328,1 argue that this text was the preliminary draft of the preserved one, most of which was composed after 1338. A thorough revision of the work was undertaken at an indeterminate date before 1344. It is also argued that the final form of the work was probably due to the request of solar and lunar tables made to Levi by “great and noble Christians” around 1332. (shrink)

In this paper I shall examine the philosophical cosmology of medieval Jewish thinkers as developed against the backdrop of their views on time and creation. I shall concentrate upon the Neoplatonic and Aristotelian traditions, with a particular eye to the interweaving of astronomy, cosmology and temporality. This interweaving occurs in part because of the influence of Greek cosmological and astronomical texts upon Jewish philosophers. The tension between astronomy and cosmology is best seen in Maimonides' discussion of creation. Gersonides, on the (...) other hand, is more willing to incorporate astronomical material into his cosmological thinking. By examining these motifs, we shall arrive at a greater understanding of the dimension of temporality within Jewish philosophy. (shrink)

Gersonides has at times been viewed as an essentially orthodox Aristotelian in his metaphysical views. This designation, however, has been challenged on a number of grounds. This paper examines the way in which Gersonides revises the traditional conception of hylomorphism by positing that matter can exist without form. Motivated by a desire to reconcile Aristotelian natural philosophy with the Ptolemaic astronomical model, formless matter is seen as a necessary entity to posit in order for his cosmological model to be coherent. (...) By allowing for this exception case, Gersonides turns hylomorphism from a metaphysical principle to a general, though not universal, principle of physics that can must be revised if other observational and philosophical commitments are to be maintained, which speaks to a distinct attitude toward Aristotelian metaphysics than is otherwise assumed to be the case for Gersonides and his contemporaries. (shrink)