Gersonides (1288–1344)

French-born Jewish philosopher and astrologer who argued that reason and the Torah are not in contradiction. His major work Sefer Milhamot Ha-Shem/The War of the Lord (1329) is a synthesis of traditional Jewish teaching with Aristotelian philosophy, as interpreted by Averroës and Moses Maimonides, although Gersonides's philosophy tends to dominate and go against traditional theology. He emphasized empirical observation, invented an instrument to measure the height of stars above the horizon, and challenged several of Ptolemy's principles of planetary movement.

In six books, The War of the Lord deals with immortality, prophecy, divine knowledge, divine providence, astronomy and astrology, and creation. Writing in a technical, analytic style, Gersonides argued that heavenly bodies ‘systematically direct’ human activities and thought, and that this was their purpose, their paths having been established by God to benefit life on earth. God's knowledge of human events is limited to knowledge of astrological conditions. But astrological influence (which is transmitted by stellar radiation) does not preclude human freedom, because our ability to choose has also been given to us by God to help us ‘to correct, as far as possible, the misfortunes that befall us’. A significant thinker in the medieval Jewish tradition, he was often cited and influenced philosophers such as Leibniz and Spinoza.

Gersonides was born in Provence, France, at that time a centre of Jewish intellectual activity. He also wrote works on logic and mathematics – Sefer Ha-heqesh Ha-yashar/On Valid Syllogisms (1319) and Sefer Ma'aseh Hoshev/The Work of a Counter (1321) – and biblical commentaries – Perush 'al Sefer lyob/Commentary on Job (1325) and Perush 'al Sefer Ha-Torah/Commentary on the Torah (1329–38).