UCL Hebrew & Jewish Studies


Isaac Israeli 'Yesod Olam'


In 1309/10 CE (5070 Anno Mundi), Isaac ben Joseph Israeli of Toledo, Spain composed the scientific treatise Yesod Olam (The Foundation of the World). Book 4 of the work teaches, primarily, the principles of the Jewish calendar and their application. Books 1 – 3 discuss mathematics, cosmography, geography and astronomy at length, ostensibly as preparation for Book 4. Book 5 contains over 50 tables, preceded by chapters explaining their use.

Editing the text: Urtext and Manuscript Transmission of Yesod Olam

Considering all of the surviving manuscripts, we discerned three medieval versions and various syntheses of these. One version is close to the original, while the other two are changed, one less, one more. We came to understand pedagogical and other reasons behind many of the changes. And we offer a system for coming close to recovering the original text.

Linguistics: Transmitting Medieval Mathematics and Science in Hebrew

We found that Israeli is nuanced in his use of scientific and mathematical vocabulary. Also, of the various approaches to Hebrew translation of technical terms, Israeli coins several terms on the basis of biblical Hebrew or on the basis of Arabic, but in many cases he uses the Hebrew terminology of his predecessors. We are preparing a lexicon in which we explain the origin and nuanced meaning of Israeli’s technical terms.

a rare example of a correct rendering of the Pythagorean Theorem diagram in the chain of the transmission of Yesod Olam.  © The British Library Board MS Add. 15977 f. 15r


Mapping Israeli’s use of Euclid’s Elements

We discovered that Book 1 includes a partial, non-linear, transmission of Euclid’s Elements. We map the correspondence between the Euclidian material and Israeli’s lessons. Israeli’s transmission is independent of any other known Hebrew transmissions of the seminal Euclidean text. Linguistic evidence suggests that Israeli’s Hebrew version was made from an Arabic source. This fits well with the cultural context.

Isaac Israeli and Rabbi Asher b. Yehiel (‘Rosh’): cultural struggle over the place of science in Judaism

We traced the origins and motives of the prevalent myth that Israeli was a disciple of Rabbi Asher b. Yehiel (‘Rosh’), the chief rabbi of Israeli’s hometown Toledo. We concluded that the two did not have a personal connection, and were on opposite sides of a cultural struggle: Israeli was a proponent of the classical Sephardic (= Jewish Iberian) view that science and Judaism should be integrated, whereas Rosh – who was not Sephardic, but an Ashkenazic (= Jewish Germanic) transplant – was opposed. Yesod Olam, which contains vastly more mathematics and science than necessary for calendar calculations, can be seen as Israeli’s attempt to perpetuate the Sephardic tradition of science-Judaism synthesis by imbedding it in a work on the calendar, the latter being relevant to Jewish law.

Research in this area was carried out by Dr Israel Sandman and Dr Ilana Wartenberg, who are preparing a critical edition and annotated English translation of Israeli’s ‘Introduction’ and ‘Book 1’, accompanied by a scientific commentary and a lexicon. In addition, they have already published a number of articles in this research area, and have more studies and texts, including an edition and translation of Yesod Olam Book 4, Chapters 7, 8, and 17, in preparation.