Isaac ibn al-Ahdab

Itzḥak ben Shlomo ibn al-Aḥdab (or ibn al-Ḥadib) ben Tzaddiq ha-Sefardi (Hebrew: יצחק בן שלמה בן צדיק אלאחדב הספרדי‎, c. 1350 – c. 1426) was a Jewish mathematician, astronomer, and poet.[1]

Ibn al-Aḥdab was born in Castile to a prominent Jewish family. He was a student of Judah ben Asher II, the great-grandson of Asher ben Yeḥiel of Cologne, who was killed in the anti-Jewish massacres of 1391. By 1396 Ibn al-Aḥdab had fled Spain and was in Sicily, where he lived (in Syracuse and Palermo) until his death around 1426.[2]


He studied the algebra of Maghrebi mathematician Ibn al-Bannā and published The Epistle of the Number, a translation and detailed commentary on Ibn al-Bannā's 13th century treatise Talḵīṣ ʿAmal al-Ḥisāb ("A summary of the operations of calculation").[3] The work is notable in being the first known Hebrew-language treatise to include extensive algebraic theories and operations.[4][5]

His main astronomical work was Oraḥ selulah, a set of tables in Hebrew for conjunctions and oppositions of the Sun and the Moon.[6]


  1. ^ Raanan, Ora, ed. (1988). The Poems of Iṣḥak ben Shlomo Al-Aḥdab (in Hebrew). Lod: Mekhon Haberman le-meḥḳere sifrut.
  2. ^ Steinschneider, M. (1964). Mathematik bei den Juden (in German) (2 ed.). Hildensheim. p. 168.
  3. ^ Katz, Victor (2016). "The Mathematical Cultures of Medieval Europe". History and Pedagogy of Mathematics.
  4. ^ Wartenberg, Ilana (2015). The epistle of the number, by Ibn al-Ahdab. Perspectives on Society and Culture. Piscataway: Gorgias Press. ISBN 978-1-4632-0417-4.
  5. ^ Reif, Stefan C. (1997). Hebrew manuscripts at Cambridge University Library: a description and introduction. University of Cambridge Oriental Publications. 52. Cambridge University Press. ISBN 978-0521583398.
  6. ^ Goldstein, Bernard R.; Chabás, José (2006). "Isaac ibn al-Ḥadib and Flavius Mithridates: The Diffusion of an Iberian Astronomical Tradition in the Late Middle Ages". Journal for the History of Astronomy. 37 (127): 147–172. Bibcode:2006JHA....37..147G. doi:10.1177/002182860603700202. ISSN 0021-8286. S2CID 220913612.