Editing Gersonides

{{Short description|Medieval Jewish philosopher}}
{{For|the printers of Hebrew books|Gersonides (printers)}}
{{Infobox philosopher
| birth_name       = Levi ben Gershon (לוי בן גרשון)
| region           = [[Jewish philosophy]]
| era              = [[Medieval philosophy]]
| name             = Gersonides
| image            = 
| caption          = 
| birth_date       = 1288
| birth_place      = [[Bagnols-sur-Cèze]]
| death_date       = {{death year and age|1344|1288}}
| death_place      = [[Perpignan]]
| school_tradition =
| main_interests   = [[Religious philosophy]], [[mathematics]]
| notable_ideas    = 
| influences       = 
| influenced       = 
}}

'''Levi ben Gershon''' (1288 – 20 April 1344), better known by his [[Greek language|Graecized]] name as '''Gersonides''', or by his Latinized name '''Magister Leo Hebraeus''',<ref>{{Cite book|url=https://books.google.com/books?id=sFztBAAAQBAJ&pg=PA387|title=Philosophy in the Middle Ages: The Christian, Islamic, and Jewish Traditions|isbn=9781603844512|last1=Hyman|first1=Arthur|last2=Walsh|first2=James J.|last3=Williams|first3=Thomas|date=24 September 2010|publisher=Hackett }}</ref> or in [[Hebrew language|Hebrew]] by the abbreviation of first letters as '''''R'''a'''LB'''a'''G''''',<ref>"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: {{Cite book |last=Rubin |first=Aaron D. |title=Encyclopedia of Hebrew language and linguistics |date=2013 |publisher=Brill |isbn=978-90-04-17642-3 |editor-last=Khan |editor-first=Geoffrey |volume=1 |location=Leiden; Boston |pages=2 |chapter=Abbreviations}})</ref> was a medieval French Jewish [[philosopher]], Talmudist, [[mathematician]], [[physician]] and [[astronomer]]/[[astrologer]]. He was born at [[Bagnols-sur-Cèze|Bagnols]] in [[Languedoc]], [[France]]. According to [[Abraham Zacuto]] and others, he was the son of [[Gerson ben Solomon Catalan]].

==Biography==
As in the case of the other [[medieval]] [[Jewish philosophy|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. It has been suggested{{by whom|date=September 2016}} 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 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.

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|Abarbanel]], [[Chisdai Crescas]], and [[Isaac ben Sheshet|Rivash]], the latter accusing him of [[heresy]] and almost banning his works.<ref>The Rishonim, The Artscroll history series, Pg. 179</ref>

==Philosophical and religious works==
{{Jewish philosophy|expanded=Medieval}}
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 the Lord"), and occupied twelve years in composition (1317–1329). A portion of it, containing an elaborate survey of [[astronomy]] as known to the [[Arab]]s, was translated into Latin in 1342 at the request of [[Pope Clement VI]].

''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.<ref>{{Cite book|first=Samuel |last=Taikh |author2=Hersh Goldwurm |date=2001 |title=The Rishonim: biographical sketches of the prominent early rabbinic sages and leaders from the tenth-fifteenth centuries |location=[[Brooklyn]] |publisher=[[Mesorah Publications]] |page=182 |oclc=60850988}}</ref>  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]] 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 decide 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 [[Neoplatonist]]s 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 commentaries on the [[Pentateuch]], [[Book of Joshua|Joshua]], [[Book of Judges|Judges]], [[Books of Samuel|I & II Samuel]], [[Books of Kings|I & II Kings]], [[Book of Proverbs|Proverbs]], [[Book of Job|Job]], [[Ecclesiastes]], [[Song of Songs]], [[Book of Ruth|Ruth]], [[Book of Esther|Esther]], [[Book of Daniel|Daniel]], [[Ezra–Nehemiah|Ezra-Nehemiah]], and [[Books of Chronicles|Chronicles]]. He makes reference to a commentary on [[Isaiah]], but it is not extant.

===Views on God and omniscience===
In contrast to the [[theology]] 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 [[Omniscience|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."<ref>{{Cite book|first=Louis |last=Jacobs |author-link=Louis Jacobs |title=God, Torah, Israel: traditionalism without fundamentalism |publisher=Hebrew Union College Press |location=[[Cincinnati]] |date=1990 |isbn=978-0-87820-052-8 |oclc=21039224}}{{Page needed|date=September 2010}}</ref>

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".<ref>{{Cite book|first=Julius |last=Guttmann |author-link=Julius Guttmann |title=Philosophies of Judaism: The History of Jewish Philosophy from Biblical Times to Franz Rosenzweig |publisher=[[Henry Holt and Company|Holt, Rinehart and Winston]] |location=[[New York City]] |date=1964 |pages=150–151 |oclc=1497829}}</ref>

: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 [[J. David Bleich|Rabbi Bleich]] indicates, and it enjoys the support of two highly respected [[Acharonim]], Rabbi [[Isaiah Horowitz|Yeshayahu Horowitz]] (''Shelah haKadosh'') and Rabbi [[Chaim ibn Attar]] (''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.<ref>''Tradition: A Journal of Orthodox Jewish Thought'', Vol. 31, No.2, Winter 1997, From ''Divine Omniscience and Free Will'', Cyril Domb, pp.&nbsp;90–91{{Verify source|what is the title and page number for the magazine article; is cyril domb's work a book, magazine?|date=April 2009}}</ref>

Rabbi [[Isaiah Horowitz|Yeshayahu 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 theology#Judaism|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 his lifetime. For Gersonides, [[Seymour Feldman]] points out, <blockquote>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.<ref>{{Cite book|first=Levi |last=ben Gershom |others=trans. Seymour Feldman |title=The Wars of the Lord: Book one, Immortality of the soul |publisher=[[Jewish Publication Society of America]] |location=[[Philadelphia]] |date=1984 |page=[https://books.google.com/books?id=job_de-tUvcC&pg=PA81 81] |isbn=978-0-8276-0220-5 |oclc=220214037}}</ref></blockquote>

===Talmudic works===
Gersonides was the author of the following Talmudic and halakhic works: 
*''Shaarei Tsedek'' (published at Leghorn, 1800): a commentary on the thirteen halachic rules of [[Rabbi 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.<ref>{{Citation |last=Kellner |first=Menachem |title=INTRODUCTION |date=2010-07-01 |work=Torah in the Observatory: Gersonides, Maimonides, Song of Songs |pages=11 |url=https://www.degruyter.com/document/doi/10.1515/9781618110183-003/html |access-date=2025-03-02 |publisher=Academic Studies Press |language=en |doi=10.1515/9781618110183-003 |isbn=978-1-61811-018-3|url-access=subscription }}</ref>

==Works in mathematics and astronomy/astrology==
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.<ref name="Simonson.2000"/>

Gersonides wrote ''Maaseh Hoshev'' in 1321 dealing with arithmetical operations including extraction of [[Square root|square]] and [[cube root]]s, 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.<ref name=induction>{{cite journal|title=Rabbi Levi Ben Gershon and the Origins of Mathematical Induction|first=Nachum L.|last=Rabinovitch|journal=[[Archive for History of Exact Sciences]]|volume=6|number=3|year=1970|pages=237–248|doi=10.1007/BF00327237|jstor=41133303|s2cid=119948133}}</ref>  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 [[Abraham ibn Ezra|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 [[sine table]]s.<ref name="Simonson.2000">{{cite journal | url=http://web.stonehill.edu/compsci/Shai_papers/MathofLevi.pdf | author=Charles G. Simonson | title=The Mathematics of Levi ben Gershon, the Ralbag | journal=Bekhol Derakhekha Daehu | publisher=Bar-Ilan University Press | volume=10 | pages=5&ndash;21 | date=Winter 2000 }}</ref>

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<sup>''m''</sup>·3<sup>''n''</sup>. 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).<ref>{{Cite journal|first=Ivar|last=Peterson|title=Medieval Harmony|url=http://www.maa.org/mathland/mathtrek_1_25_99.html|journal=Ivar Peterson's MathTrek|access-date=2010-12-26|archive-date=2012-08-04|archive-url=https://archive.today/20120804182624/http://www.maa.org/mathland/mathtrek_1_25_99.html|url-status=dead}}</ref>

He is also credited to have invented the [[Jacob's staff]],<ref>{{Cite journal|first=David G. |last=Krehbiel |title=Jacob's Staff |url=http://www.surveyhistory.org/jacob's_staff1.htm |journal=The Ontario Land Surveyor |date=Spring 1990}}</ref> an instrument to measure the angular distance between celestial objects. It is described as consisting {{Quote|…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.<ref>[http://mathshistory.st-andrews.ac.uk/Biographies/Levi.html Levi ben Gerson]</ref>}}

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.<ref name=induction/>

The lunar crater [[Rabbi Levi (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:{{Quote|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.<ref>{{Cite book|first=Julius |last=Guttmann |author-link=Julius Guttmann |title=Philosophies of Judaism: The History of Jewish Philosophy from Biblical Times to Franz Rosenzweig |publisher=[[Henry Holt and Company|Holt, Rinehart and Winston]] |location=[[New York City]] |date=1964 |page=217 |oclc=1497829}}</ref>}}

===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,<ref>Albert Van Helden, ''Measuring the Universe: Cosmic Dimensions from Aristarchus to Halley'' (Chicago: The University of Chicago Press, 1985), p.&nbsp;40.</ref> 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 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 [[Copernican heliocentrism|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 [[Nicolaus Copernicus|Copernicus]] and [[Johannes Kepler|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.<ref>[[Yuval Ne'eman]]: Astronomy in Sefarad [http://wise-obs.tau.ac.il/judaism/sefarad.html]</ref>

==In modern fiction==
Gersonides is an important character in the novel ''[[The Dream of Scipio (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 ==

* 1985: [[National Jewish Book Award]] Scholarship for ''The Wars of the Lord''<ref>{{Cite web|url=https://www.jewishbookcouncil.org/awards/national-jewish-book-awards/past-winners?category=30775|title=Past Winners|website=Jewish Book Council|language=en|access-date=2020-01-24}}</ref>

==References==
{{Reflist}}

==Further reading==
*"Gersonides". ''The Encyclopaedia Judaica''. Keter Publishing.
*[[Seymour Feldman|Feldman, Seymour]].  ''The Wars of the Lord'' (3 volumes). Jewish Publication Society.
*Gerson Lange (ed. &amp; transl.), ''Sefer Maassei Choscheb: Die Praxis des Rechners – Ein hebräisch-arithmetisches Werk des Levi ben Gerschom aus dem Jahre 1321 '' (Frankfurt am Main: Buchdruckerei Louis Golde, 1909) [https://archive.org/details/sefermaasehoshev00levi online link].
*{{Cite encyclopedia |first=M. |last=Seligsohn |author-link=Max Seligsohn |author2=Kaufmann Kohler |author2-link=Kaufmann Kohler |author3=Isaac Broydé |author3-link=Isaac Broydé |title=Levi ben Gershon |url=http://jewishencyclopedia.com/view.jsp?artid=247&letter=L |encyclopedia=[[Jewish Encyclopedia]] |editor=Isidore Singer |editor-link=Isidore Singer |editor2=Cyrus Adler |editor2-link=Cyrus Adler |orig-year=c. 1916 |date=2002 |oclc=4743907 |lccn=16014703}}
*Guttman, Julius (1964). ''Philosophies of Judaism'', pp.&nbsp;214–215. JPS.
*''Lévi ben Gershom ( Gersonide ), Les Guerres du Seigneur, livres III et IV'', introduction, traduction [française] et notes par [[Charles Touati]]. Paris-La Haye, Mouton & Co., 1968.
*[[Charles Touati]], ''La pensée philosophique et théologique de Gersonide'', Paris, 1973.
*{{cite book |url=https://books.google.com/books?id=cfQdAAAAMAAJ&q=Norbert+Max+Samuelson |title=Gersonides' The Wars of the Lord, Treatise III: On God's knowledge |date=1977 |last=Samuelson |first=Norbert M. |author-link=Norbert M. Samuelson|publisher=Pontifical Institute of Mediaeval Studies |location=Toronto |isbn=978-0-88844-268-0}}
*Bernard R. Goldstein (ed. &amp; transl.), ''The Astronomy of Levi ben Gerson (1288-1344) - A Critical Edition of Chapters 1-20 with Translation and Commentary'' (New York: Springer-Verlag, 1985 [= ''Studies in the History of Mathematics and Physical Sciences'', nr.&nbsp;11]).
*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.
*{{Cite book|first=Samuel |last=Taikh |author2=Hersh Goldwurm |date=2001 |title=The Rishonim: biographical sketches of the prominent early rabbinic sages and leaders from the tenth–fifteenth centuries |location=[[Brooklyn]] |publisher=[[Mesorah Publications]] |oclc=60850988}}.
*C. Sirat, S. Klein-Braslavy, Olga Weijers, Ph. Bobichon, G. Dahan, M. Darmon, G. Freudenthal R. Glasner, M. Kellner, J.-L. Mancha,''Les méthodes de travail de Gersonide et le maniement du savoir chez les scolastiques'', Librairie philosophique Vrin, Paris, 2003.

==External links==
*{{Commons category inline}}
*[http://plato.stanford.edu/entries/gersonides/ Stanford Encyclopedia of Philosophy]
* {{cite encyclopedia | editor = Thomas Hockey | display-editors = etal | last = Rudavsky | first = Tamar M. | title=Gersonides: Levi ben Gerson | encyclopedia = The Biographical Encyclopedia of Astronomers | publisher = Springer | date = 2007 | location = New York | url=http://islamsci.mcgill.ca/RASI/BEA/Gersonides_BEA.htm | isbn=978-0-387-31022-0}} ([http://islamsci.mcgill.ca/RASI/BEA/Gersonides_BEA.pdf PDF version])
*[http://www.teachittome.com/seforim2/seforim/milchamos_hashem.pdf Milhamot HaShem First Edition] ([[PDF]]) This is the text excluding the astronomical text (Book V, Part I).  The quality varies.
* {{MacTutor Biography|id=Levi}}
*[http://research.haifa.ac.il/~kellner/bibgers.html Detailed bibliography of works on and by Gersonides] {{Webarchive|url=https://web.archive.org/web/20160303171552/http://research.haifa.ac.il/~kellner/bibgers.html |date=2016-03-03 }}
*[https://books.google.com/books?id=VKU8AAAAYAAJ&q=%D7%9E%D7%9C%D7%97%D7%9E%D7%AA%20%D7%94%D7%A9%D7%9D Milchamot Hashem]
*{{Cite EB1911 |last=Abrahams |first=Israel |author-link=Israel Abrahams |wstitle=Gersonides, Levi |short=x}}

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