Levi ben Gershon ("Levi son of Gerson"), better known as Gersonides or the Ralbag (1288-1344), was a famous rabbi, philosopher, mathematician, astronomer and Talmudist. He was born at Bagnols in Languedoc, France.

Biography

As in the case of the other medieval Jewish philosophers little is known of his life. His family had been distinguished for piety and exegetical skill in Talmud, but though he was known in the Jewish community by commentaries on certain books of the Bible, he never seems to have accepted any rabbinical post. Possibly the freedom of his opinions may have put obstacles in the way of his preferment. He is known to have been at Avignon and Orange during his life, and is believed to have died in 1344, though Zacuto asserts that he died at Perpignan in 1370.

Works

Philosophical and religious works

Part of his writings consist of commentaries on the portions of Aristotle then known, or rather of commentaries on the commentaries of Averroes. Some of these are printed in the early Latin editions of Aristotle’s works. His most important treatise, that by which he has a place in the history of philosophy, is entitled Sefer Milhamot Ha-Shem , ("The Wars of God"), and occupied twelve years in composition (1317—1329). A portion of it, containing an elaborate survey of astronomy as known to the Arabs, was translated into Latin in 1342 at the request of Pope Clement VI.

The Milhamot is throughout modeled after the plan of the great work of Jewish philosophy, the Guide of the Perplexed of Maimonides, and may be regarded as an elaborate criticism from the more philosophical point of view (mainly Averroistic) of the syncretism of Aristotelianism

1. the doctrine of the soul, in which Gersonides defends the theory of impersonal reason as mediating between God and man, and explains the formation of the higher reason (or acquired intellect, as it was called) in humanity — his view being thoroughly realist and resembling that of Avicebron;

2. prophecy;3. and 4. God's knowledge of facts and providence, in which is advanced the curious theory that God does not know individual facts, and that, while there is general providence for all, special providence only extends to those whose reason has been enlightened;

5. celestial substances, treating of the strange spiritual hierarchy which the Jewish philosophers of the middle ages accepted from the Neoplatonists and the pseudo-Dionysius, and also giving, along with astronomical details, much of astrological theory; and

6. creation and miracles, in respect to which Gersonides deviates widely from the position of Maimonides.

Gersonides was also the author of a commentary on the Pentateuch and other exegetical and scientific works.

Views on God and omnipotence

In contrast to the theology held by Orthodox Judaism, Gersonides held with those who denied God's omnipotence. "Gersonides, bothered by the old question of how God's foreknowledge is compatible with human freedom, holds that what God knows beforehand is all the choices open to each individual. God does not know, however, which choice the individual, in his freedom, will make." (Louis Jacobs, God, Torah, Israel: Traditionalism without Fundamentalism)

Another classical Jewish proponent of limited theism was Abraham ibn Daud. "Whereas the earlier Jewish philosophers extended the omniscience of God to include the free acts of man, and had argued that human freedom of decision was not affected by God's foreknowledge of its results, Ibn Daud, evidently following Alexander of Aphrodisias, excludes human action from divine foreknowledge. God, he holds, limited his omniscience even as He limited His omnipotence in regard to human acts". (Philosophies of Judaism, Julius

"The view that God does not have foreknowledge of moral decisions which was advanced by ibn Daud and Gersonides (Levi ben Gershom) is not quite as isolated as Rabbi Bleich indicates, and it enjoys the support of two highly respected Ahronim, Rabbi Yeshayahu Horowitz (Shelah haKadosh) and Rabbi Chaim ibn Atar (Or haHayim haKadosh). The former takes the views that God cannot know which moral choices people will make, but this does not impair His perfection. The latter considers that God could know the future if He wished, but deliberately refrains from using this ability in order to avoid the conflict with free will." (Tradition: A Journal of Orthodox Jewish Thought, Vol. 31, No.2, Winter 1997, From Divine Omniscience and Free Will, Cyril Domb, p.90-91)

See further discussion in Free will In Jewish thought.

Views of the afterlife

Gersonides posits that people's souls are composed of two parts: a material, or human, intellect; and an acquired, or agent, intellect. The material intellect is inherent in every person, and gives people the capacity to understand and learn. This material intellect is mortal, and dies with the body. However, he also posits that the soul also has an acquired intellect. This survives death, and can contain the accumulated knowledge that the person acquired during their lifetime. For Gersonides, Seymour Feldman points out, "Man is immortal insofar as he attains the intellectual perfection that is open to him. This means that man becomes immortal only if and to the extent that he acquires knowledge of what he can in principle know, e.g. mathematics and the natural sciences. This knowledge survives his bodily death and constitutes his immortality." (Gersonides, Trans. Seymour Feldman Wars of the Lord, Book 1, p. 81, JPS, 1984)

Works in mathematics and astronomy

Gersonides wrote Book of Numbers in 1321 dealing with arithmetical operations, including extraction of roots. Also, in 1342, he wrote On Sines, Chords and Arcs, which examined trigonometry, in particular proving the sine theorem for plane triangles and giving five figure sine tables.

One year later, at the request of the bishop of Meaux, he wrote The Harmony of Numbers which is a commentary on the first five books of Euclid.

He also invented Jacob's staff, an instrument to measure the angular distance between celestial objects. It is described as consisting

.. of a staff of 4.5 feet (1.4 m) long and about one inch (2.5 cm) wide, with six or seven perforated tablets which could slide along the staff, each tablet being an integral fraction of the staff length to facilitate calculation, used to measure the distance between stars or planets, and the altitudes and diameters of the Sun, Moon and stars.

Levi observed a solar eclipse in 1337. After he had observed this event he proposed a new theory of the sun which he proceeded to test by further observations. Another eclipse observed by Levi was the eclipse of the Moon on 3 October 1335. He described a geometrical model for the motion of the Moon and made other astronomical observations of the Moon, Sun and planets using a camera obscura.

Some of his beliefs were well wide of the truth, such as his belief that the Milky Way was on the sphere of the fixed stars and shines by the reflected light of the Sun.

Bibliography

• "Gersonides". The Encyclopaedia Judaica. Keter Publishing.
• Eisen, Robert (1995). Gersonides on Providence, Covenant, and the Chosen People: A Study in Medieval Jewish Philosophy and Biblical Commentary. State University of New York.
• Guttman, Julius (1964). Philosophies of Judaism, p.214/215. JPS.
• Feldman, Seymour. The Wars of the Lord (3 volumes). Jewish Publication Society.

לוי בן גרשום ゲルソニデス