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Levi ben Gershon (1288 – 20 April 1344), better known by his Greek language name as Gersonides, or by his Latinized name Magister Leo Hebraeus, or in Hebrew language by the abbreviation of first letters as R aLB aG,"Ralbag" is the acronym of "Rabbi Levi Ben Gershon", with vowels added to make it easily pronounceable, the normal traditional Jewish practice with the names of prominent Rabbis. (See: ) was a medieval French Jewish philosopher, Talmudist, mathematician, physician and astronomer/astrologer. He was born at Bagnols in Languedoc, France. According to Abraham Zacuto and others, he was the son of Gerson ben Solomon Catalan.
Gersonides is known for his unorthodox views and rigid Aristotelianism, which eventually led him to rationalize many of the miracles in the Bible. His commentary on the Bible was sharply criticized by the most prominent scholars, such as Isaac Abarbanel, Chisdai Crescas, and Rivash, the latter accusing him of heresy and almost banning his works.The Rishonim, The Artscroll history series, Pg. 179
The Wars of the Lord is modeled after the plan of the great work of Jewish philosophy, the Guide for the Perplexed of Maimonides. It may be regarded as a criticism of some elements of Maimonides' syncretism of Aristotelianism and rabbinic Jewish thought. Ralbag's treatise strictly adhered to Aristotelian thought. The Wars of the Lord review:
Gersonides was also the author of commentaries on the Pentateuch, Joshua, Judges, I & II Samuel, I & II Kings, Proverbs, Job, Ecclesiastes, Song of Songs, Ruth, Esther, Daniel, Ezra-Nehemiah, and Chronicles. He makes reference to a commentary on Isaiah, but it is not extant.
Another neoclassical Jewish proponent of self-limited omniscience 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".
Rabbi Isaiah Horowitz explained the apparent paradox of his position by citing the old question, "Can God create a rock so heavy that He cannot pick it up?" He said that we cannot accept free choice as a creation of God's, and simultaneously question its logical compatibility with omnipotence.
See further discussion in Free will in Jewish thought.
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 wrote Maaseh Hoshev in 1321 dealing with arithmetical operations including extraction of Square root and , various algebraic identities, certain sums including sums of consecutive integers, squares, and cubes, binomial coefficients, and simple combinatorial identities. The work is notable for its early use of proof by mathematical induction, and pioneering work in combinatorics. The title Maaseh Hoshev literally means the Work of the thinker, but it is also a pun on a biblical phrase meaning "clever work". Maaseh Hoshev is sometimes mistakenly referred to as Sefer Hamispar (The Book of Number), which is an earlier and less sophisticated work by Rabbi Abraham ben Meir ibn Ezra (1090–1167). In 1342, Gersonides wrote On Sines, Chords and Arcs, which examined trigonometry, in particular proving the sine law for plane triangles and giving five-figure .
One year later, at the request of the bishop of Meaux, he wrote The Harmony of Numbers in which he considers a problem of Philippe de Vitry involving so-called harmonic numbers, which have the form 2 m·3 n. The problem was to characterize all pairs of harmonic numbers differing by 1. Gersonides proved that there are only four such pairs: (1,2), (2,3), (3,4) and (8,9).
He is also credited to have invented the Jacob's staff, an instrument to measure the angular distance between celestial objects. It is described as consisting
Gersonides observed a solar eclipse on March 3, 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 Gersonides 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.
Gersonides was also the earliest known mathematician to have used the technique of mathematical induction in a systematic and self-conscious fashion and anticipated Galileo's error theory.
The lunar crater Rabbi Levi is named after him.
Gersonides believed that astrology was real, and developed a naturalistic, non-supernatural explanation of how it works. Julius Guttman explained that for Gersonides, astrology was:
Using data he collected from his own observations, Gersonides refuted Ptolemy's model in what the notable physicist Yuval Ne'eman has considered as "one of the most important insights in the history of science, generally missed in telling the story of the transition from epicyclic corrections to the geocentric model to Copernicus' heliocentric model". Ne'eman argued that after Gersonides reviewed Ptolemy's model with its epicycles he realized that it could be checked, by measuring the changes in the apparent brightnesses of Mars and looking for cyclical changes along the conjectured epicycles. These thus ceased being dogma, they were a theory that had to be experimentally verified, "à la Popper". Gersonides developed tools for these measurements, essentially pinholes and the camera obscura.
The results of his observations did not fit Ptolemy's model at all. Concluding that the model was inadequate, Gersonides tried (unsuccessfully) to improve on it. That challenge was finally answered, of course, by Copernicus and Johannes Kepler three centuries later, but Gersonides was the first to falsify the Alexandrian dogma - the first known instance of modern falsification philosophy. Gersonides also showed that Ptolemy's model for the lunar orbit, though reproducing correctly the evolution of the Moon's position, fails completely in predicting the apparent sizes of the Moon in its motion. Unfortunately, there is no evidence that the findings influenced later generations of astronomers, even though Gersonides' writings were translated and available.Yuval Ne'eman: Astronomy in Sefarad [1]
Estimation of stellar distances and refutation of Ptolemy's model
Gersonides appears to be the only astronomer before modern times to have surmised that the fixed stars are much further away than the planets. Whereas all other astronomers put the fixed stars on a rotating sphere just beyond the outer planets, Gersonides estimated the distance to the fixed stars to be no less than 159,651,513,380,944 earth radii,Albert Van Helden, Measuring the Universe: Cosmic Dimensions from Aristarchus to Halley (Chicago: The University of Chicago Press, 1985), p. 40. or about 100,000 lightyears in modern units.
In modern fiction
Gersonides is an important character in the novel The Dream of Scipio by Iain Pears, where he is depicted as the mentor of the protagonist Olivier de Noyen, a non-Jewish poet and intellectual. A (fictional) encounter between Gersonides and Pope Clement VI at Avignon during the Black Death is a major element in the book's plot.
Awards
Further reading
Norbert M. Samuelson (1977). 9780888442680, Pontifical Institute of Mediaeval Studies. . ISBN 9780888442680
External links
Categories: 1288 Births, 1344 Deaths, 14th-century French Mathematicians, 14th-century French Philosophers, 14th-century French Rabbis, 14th-century Jewish Theologians, Bible Commentators, French Astrologers, 14th-century Astrologers, Medieval French Astronomers, Jewish Astronomers, Medieval Jewish Philosophers, Philosophers Of Judaism, 14th-century Jewish Biblical Scholars
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