Gersonides | |
|---|---|
| Born | Levi ben Gershon (לוי בן גרשון) 1288 |
| Died | 1344 (aged 55–56) |
| Philosophical work | |
| Era | Medieval philosophy |
| Region | Jewish philosophy |
| Main interests | Religious philosophy,mathematics |
Levi ben Gershon (1288 – 20 April 1344), better known by hisGraecized name asGersonides, or by his Latinized nameMagister Leo Hebraeus,[1] or inHebrew by the abbreviation of first letters asRaLBaG,[2] was a medieval French Jewishphilosopher, Talmudist,mathematician,physician andastronomer/astrologer. He was born atBagnols inLanguedoc,France. According toAbraham Zacuto and others, he was the son ofGerson ben Solomon Catalan.
As in the case of the othermedievalJewish 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 theBible, he never seems to have accepted any rabbinical post. It has been suggested[by whom?] that the uniqueness of his opinions may have put obstacles in the way of his advancement to a higher position or office. He is known to have been atAvignon and Orange during his life, and is believed to have died in 1344, thoughZacuto asserts that he died atPerpignan in 1370.
Gersonides is known for his unorthodox views and rigidAristotelianism, 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 asAbarbanel,Chisdai Crescas, andRivash, the latter accusing him ofheresy and almost banning his works.[3]
Part of his writings consist of commentaries on the portions ofAristotle then known, or rather of commentaries on the commentaries ofAverroes. Some of these are printed in the earlyLatin editions of Aristotle's works. His most important treatise, that by which he has a place in the history of philosophy, is entitledSefer Milhamot Ha-Shem, ("The Wars of the Lord"), and occupied twelve years in composition (1317–1329). A portion of it, containing an elaborate survey ofastronomy as known to theArabs, was translated into Latin in 1342 at the request ofPope Clement VI.
The Wars of the Lord is modeled after the plan of the great work of Jewish philosophy, theGuide for the Perplexed ofMaimonides. 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.[4] TheWars of the Lord review:
Gersonides was also the author of commentaries on thePentateuch,Joshua,Judges,I & II Samuel,I & II Kings,Proverbs,Job,Ecclesiastes,Song of Songs,Ruth,Esther,Daniel,Ezra-Nehemiah, andChronicles. He makes reference to a commentary onIsaiah, but it is not extant.
In contrast to thetheology held by other Jewish thinkers, Jewish theologianLouis Jacobs argues, Gersonides held that God does not have complete foreknowledge of human acts. "Gersonides, bothered by the old question of how God'sforeknowledge 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."[5]
Another neoclassical Jewish proponent of self-limited omniscience wasAbraham ibn Daud. "Whereas the earlier Jewish philosophers extended theomniscience 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 followingAlexander 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".[6]
RabbiYeshayahu 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 inFree will in Jewish thought.
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 his 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.[8]
Gersonides was the author of the following Talmudic and halakhic works:
Only the first work is extant.[9]
Gersonides was the first to make a number of major mathematical and scientific advances, though since he wrote only in Hebrew and few of his writings were translated to other languages, his influence on non-Jewish thought was limited.[10]
Gersonides wroteMaaseh Hoshev in 1321 dealing with arithmetical operations including extraction ofsquare andcube roots, 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 bymathematical induction, and pioneering work in combinatorics.[11] 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 byRabbi Abraham ben Meir ibn Ezra (1090–1167). In 1342, Gersonides wroteOn Sines, Chords and Arcs, which examinedtrigonometry, in particular proving thesine law for plane triangles and giving five-figuresine tables.[10]
One year later, at the request of thebishop of Meaux, he wroteThe Harmony of Numbers in which he considers a problem ofPhilippe de Vitry involving so-calledharmonic numbers, which have the form 2m·3n. 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).[12]
He is also credited to have invented theJacob's staff,[13] 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.[14]
Gersonides observed asolar 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 acamera obscura. Some of his beliefs were well wide of the truth, such as his belief that theMilky 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.[11]
The lunar craterRabbi Levi is named after him.
Gersonides believed thatastrology was real, and developed a naturalistic, non-supernatural explanation of how it works.Julius Guttman explained that for Gersonides, astrology was:
founded on the metaphysical doctrine of the dependence of all earthly occurrences upon the heavenly world. The general connection imparted to the prophet by the active intellect is the general order of the astrological constellation. The constellation under which a man is born determines his nature and fate, and constellations as well determine the life span of nations. …The active intellect knows the astrological order, from the most general form of the constellations to their last specification, which in turn contains all of the conditions of occurrence of a particular event. Thus, when a prophet deals with the destiny of a particular person or human group, he receives from the active intellect a knowledge of the order of the constellations, and with sufficient precision to enable him to predict its fate in full detail. …This astrological determinism has only one limitation. The free will of man could shatter the course of action ordained for him by the stars; prophecy could therefore predict the future on the basis of astrological determination only insofar as the free will of man does not break through the determined course of things.[15]
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,[16] or about 100,000 lightyears in modern units.
Using data he collected from his own observations, Gersonides refuted Ptolemy's model in what the notable physicistYuval 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 toCopernicus' 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 thecamera 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, byCopernicus andKepler 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.[17]
Gersonides is an important character in the novelThe Dream of Scipio byIain 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 andPope Clement VI atAvignon during theBlack Death is a major element in the book's plot.
Media related toGersonides at Wikimedia Commons
