David, the father of Jewish philosophy, was almost unknown until the latter part of the 19th century. The publication of Judah Barzilai's commentary to the Sefer Yezirah ("Meḳiẓe Nirdamim", 1885), in which is found a poor Hebrew translation of the ninth and tenth chapters of David's philosophical work, first brought the latter into notice. Barzilai says that he does not know whether David was one of the Geonim, but claims to have heard that Saadia had known him and had profited by his lessons. Pinsker and Grätz, confounding him with Daniel ha-Babli of Cairo, make him a Mohammedan convert to Karaism, on the ground that he is quoted by Karaite scholars, and is called by Hadasi "ger ẓedeḳ" (pious proselyte).