Gersonides
Encyclopedia
Levi ben Gershon, better known by his Latinised name as Gersonides or the abbreviation of first letters as RaLBaG (1288–1344), philosopher, Talmudist, mathematician
Mathematician
A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

, astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

/astrologer
Astrologer
An astrologer practices one or more forms of astrology. Typically an astrologer draws a horoscope for the time of an event, such as a person's birth, and interprets celestial points and their placements at the time of the event to better understand someone, determine the auspiciousness of an...

. He was born at Bagnols
Bagnols-sur-Cèze
Bagnols-sur-Cèze is a commune in the Gard department in the Languedoc-Roussillon région in southern France.-History:A small regional center, Bagnols-sur-Cèze was quite certainly a Roman town before the main part was built in the 13th century around a central arcaded square that is still preserved...

 in Languedoc
Languedoc
Languedoc is a former province of France, now continued in the modern-day régions of Languedoc-Roussillon and Midi-Pyrénées in the south of France, and whose capital city was Toulouse, now in Midi-Pyrénées. It had an area of approximately 42,700 km² .-Geographical Extent:The traditional...

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. According to Abraham Zacuto
Abraham Zacuto
Abraham Zacuto was a Sephardi Jewish astronomer, astrologer, mathematician and historian who served as Royal Astronomer in the 15th century to King John II of Portugal. The crater Zagut on the Moon is named after him....

 and others, he was the son of Gerson ben Solomon Catalan
Gerson ben Solomon Catalan
Gerson ben Solomon Catalan was a Jewish author who lived at Arles, France in the middle of the thirteenth century. He died, possibly at Perpignan, toward the end of the thirteenth century...

.

Biography

As in the case of the other medieval Jewish philosophers
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 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
Bible
The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

, he never seems to have accepted any rabbinical post. It has been suggested that the uniqueness of his opinions may have put obstacles in the way of his preferment. He is known to have been at Avignon
Avignon
Avignon is a French commune in southeastern France in the départment of the Vaucluse bordered by the left bank of the Rhône river. Of the 94,787 inhabitants of the city on 1 January 2010, 12 000 live in the ancient town centre surrounded by its medieval ramparts.Often referred to as the...

 and Orange during his life, and is believed to have died in 1344, though Zacuto asserts that he died at Perpignan
Perpignan
-Sport:Perpignan is a rugby stronghold: their rugby union side, USA Perpignan, is a regular competitor in the Heineken Cup and seven times champion of the Top 14 , while their rugby league side plays in the engage Super League under the name Catalans Dragons.-Culture:Since 2004, every year in the...

 in 1370.

Philosophical and religious works

Part of his writings consist of commentaries on the portions of Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 then known, or rather of commentaries on the commentaries of Averroes
Averroes
' , better known just as Ibn Rushd , and in European literature as Averroes , was a Muslim polymath; a master of Aristotelian philosophy, Islamic philosophy, Islamic theology, Maliki law and jurisprudence, logic, psychology, politics, Arabic music theory, and the sciences of medicine, astronomy,...

. Some of these are printed in the early Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 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 the Lord"), and occupied twelve years in composition (1317–1329). A portion of it, containing an elaborate survey of astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 as known to the Arab
Arab
Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

s, was translated into Latin in 1342 at the request of Pope Clement VI
Pope Clement VI
Pope Clement VI , bornPierre Roger, the fourth of the Avignon Popes, was pope from May 1342 until his death in December of 1352...

.

The Wars of the Lord is modeled after the plan of the great work of Jewish philosophy, the Guide for the Perplexed of Maimonides
Maimonides
Moses ben-Maimon, called Maimonides and also known as Mūsā ibn Maymūn in Arabic, or Rambam , was a preeminent medieval Jewish philosopher and one of the greatest Torah scholars and physicians of the Middle Ages...

. It may be regarded as a criticism of some elements of Maimonides' syncretism
Syncretism
Syncretism is the combining of different beliefs, often while melding practices of various schools of thought. The term means "combining", but see below for the origin of the word...

 of Aristotelianism and rabbinic Jewish thought. Ralbag's treatise strictly adhered to Aristotelian thought. The Wars of the Lord review:
1. the doctrine of the soul, in which Gersonides defends the theory of impersonal reason as mediating between God
God
God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....

 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 theory that God does not know individual facts. 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 omniscience

In contrast to the theology
Theology
Theology is the systematic and rational study of religion and its influences and of the nature of religious truths, or the learned profession acquired by completing specialized training in religious studies, usually at a university or school of divinity or seminary.-Definition:Augustine of Hippo...

 held by other Jewish thinkers, Jewish theologian Louis Jacobs argues, Gersonides held that God does not have complete foreknowledge of human acts. "Gersonides, bothered by the old question of how God's foreknowledge
Foreknowledge
Foreknowledge may refer to* Various concepts of knowledge regarding future events:** Predestination** Prediction - Informed or uninformed guesses regarding future events...

 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."

Another neoclassical Jewish proponent of self-limited omniscience was Abraham ibn Daud
Abraham ibn Daud
Abraham ibn Daud was a Spanish-Jewish astronomer, historian, and philosopher; born at Toledo, Spain about 1110; died, according to common report, a martyr about 1180. He is sometimes known by the abbreviation Rabad I or Ravad I. His mother belonged to a family famed for its learning...

. "Whereas the earlier Jewish philosophers extended the omniscience
Omniscience
Omniscience omniscient point-of-view in writing) is the capacity to know everything infinitely, or at least everything that can be known about a character including thoughts, feelings, life and the universe, etc. In Latin, omnis means "all" and sciens means "knowing"...

 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
Alexander of Aphrodisias
Alexander of Aphrodisias was a Peripatetic philosopher and the most celebrated of the Ancient Greek commentators on the writings of Aristotle. He was a native of Aphrodisias in Caria, and lived and taught in Athens at the beginning of the 3rd century, where he held a position as head of the...

, excludes human action from divine foreknowledge. God, he holds, limited his omniscience even as He limited His omnipotence in regard to human acts".
"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
J. David Bleich
J. David Bleich is an authority on Jewish law and ethics, including Jewish medical ethics. He is rabbi of Cong. B'nei Jehuda...

 indicates, and it enjoys the support of two highly respected Achronim, Rabbi Yeshayahu Horowitz
Isaiah Horowitz
Isaiah Horowitz, , also known as the Shelah ha-Kadosh after the title of his best-known work, was a prominent Levite rabbi and mystic.-Biography:...

 (Shelah haKadosh) and Rabbi Chaim ibn Attar
Chaim ibn Attar
Chaim ben Moses ibn Attar also known as the Ohr ha-Chaim after his popular commentary on the Pentateuch, was a Talmudist and kabbalist; born at Meknes, Morocco, in 1696; died in Jerusalem, Israel July 7, 1743. He was one of the most prominent rabbis in Morocco.In 1733 he decided to leave his native...

 (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."


Rabbi Isaiah Horowitz
Isaiah Horowitz
Isaiah Horowitz, , also known as the Shelah ha-Kadosh after the title of his best-known work, was a prominent Levite rabbi and mystic.-Biography:...

 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.

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."

Works in mathematics and astronomy/astrology

Gersonides wrote Maaseh Hoshev in 1321 dealing with arithmetical operations including extraction of square
Square root
In mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x...

 and cube 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 by mathematical induction, and pioneering work in combinatorics. The title Maaseh Hoshev literally means a Work of Calculation, 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, Levi wrote On Sines, Chords and Arcs, which examined trigonometry
Trigonometry
Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

, in particular proving the sine law 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 in which he considers a problem of Philippe de Vitry
Philippe de Vitry
Philippe de Vitry was a French composer, music theorist and poet. He was an accomplished, innovative, and influential composer, and may also have been the author of the Ars Nova treatise...

 involving so-called harmonic 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).

He is also credited to have invented the Jacob's staff
Jacob's staff
The Jacob's staff, also called a cross-staff, a ballastella, a fore-staff, or a balestilha is used to refer to several things. This can lead to considerable confusion unless one clarifies the purpose for the object so named...

, an instrument to measure the angular distance between celestial objects. It is described as consisting

Levi observed a solar eclipse
Solar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

 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 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
Camera obscura
The camera obscura is an optical device that projects an image of its surroundings on a screen. It is used in drawing and for entertainment, and was one of the inventions that led to photography. The device consists of a box or room with a hole in one side...

.

Some of his beliefs were well wide of the truth, such as his belief that the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 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
Rabbi Levi (crater)
Rabbi Levi is a lunar impact crater that is located among the rugged highlands in the southeastern part of the Moon's near side. Several notable craters are located nearby, including Zagut just to the north-northwest, the heavily impacted Riccius to the southeast, and Lindenau to the northeast next...

 is named after him.

Gersonides believed that astrology
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

 was real, and developed a naturalistic, non-supernatural explanation of how it works. Julius Guttman explained that for Gersonides, astrology was:

Estimation of stellar distances and refutation of Ptolemy's model

Gersonides is the only astronomer before modern times to have estimated correctly stellar distances. Whereas all other astronomers put the stars on a rotating sphere just beyond the outer planets, Gersonides estimated the distance to the stars to be ten billion times greater, of the order of 100 light-years (in modern units).

Using data he collected from his own observations Gersonides' refuted Ptolemy's model in what the notable physicist Yuval Ne'eman
Yuval Ne'eman
Yuval Ne'eman , was a renowned Israeli theoretical physicist, military scientist, and politician. He was a minister in the Israeli government in the 1980s and early 1990s.-Biography:...

 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
Copernican heliocentrism
Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543. It positioned the Sun near the center of the Universe, motionless, with Earth and the other planets rotating around it in circular paths modified by epicycles and at uniform...

". 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, "a la Popper". R. Levi developed tools for these measurements, essentially pinholes and the camera obscura
Camera obscura
The camera obscura is an optical device that projects an image of its surroundings on a screen. It is used in drawing and for entertainment, and was one of the inventions that led to photography. The device consists of a box or room with a hole in one side...

.

The results of his observations did not fit Ptolemy's model at all. Gersonides concluded that the model was no good. He tried (unsuccessfully) to improve on it. That challenge was finally answered, of course, by Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

 three centuries later, but Gersonides was the first and only one to falsify the Alexandrian dogma - the first known instance of modern falsification philosophy. Levi 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 had an impact on later generations of astronomers, even though Gersonides' writings were translated and available.

Talmudic works

  • Shaarei Tsedek (published at Leghorn, 1800): a commentary on the thirteen halachic rules of the Tanna, R'Yishmael;
  • Mechokek Safun, an interpretation of the aggadic material in the fifth chapter of Tractate Bava Basra;
  • A commentary to tractate Berachos;
  • two responsa.

Only the first work is extant.

In modern fiction

Gersonides is an important character in the novel The Dream of Scipio
The Dream of Scipio
The Dream of Scipio is a novel by Iain Pears. It is set in Provence at three different critical moments of Western civilization -- the collapse of the Roman Empire in the fifth century, the Black Death in the fourteenth, the Second World War in the twentieth—through which the fortunes of three men...

by Iain Pears
Iain Pears
Iain Pears is an English art historian, novelist and journalist. He was educated at Warwick School, Warwick, Wadham College and Wolfson College, Oxford. Before writing, he worked as a reporter for the BBC, Channel 4 and ZDF and correspondent for Reuters from 1982 to 1990 in Italy, France, UK and...

, 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
Pope Clement VI
Pope Clement VI , bornPierre Roger, the fourth of the Avignon Popes, was pope from May 1342 until his death in December of 1352...

 at Avignon
Avignon
Avignon is a French commune in southeastern France in the départment of the Vaucluse bordered by the left bank of the Rhône river. Of the 94,787 inhabitants of the city on 1 January 2010, 12 000 live in the ancient town centre surrounded by its medieval ramparts.Often referred to as the...

 during the Black Death
Black Death
The Black Death was one of the most devastating pandemics in human history, peaking in Europe between 1348 and 1350. Of several competing theories, the dominant explanation for the Black Death is the plague theory, which attributes the outbreak to the bacterium Yersinia pestis. Thought to have...

 is a major element in the book's plot.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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