 Avicenna was the main source of an important doctrine which spread among a number of 11th- and 12th-century Jewish philosophers, as once shown by Harry A. Wolfson (Wolfson 1935): according to this doctrine, there are in man’s mind five internal senses (common sense, estimation, imagination, thought, and memory). A first trace of this doctrine was found in Bahya Ibn Paquda: however, he might have taken it from an Arabic philosophical or theological compendium inspired by Avicenna. Such occasional employment of Avicenna as a source for one particular point of a Medieval Jewish philosopher’s thought might have happened in the case of Joseph Ibn Zaddiq’s Book of the Microcosm, as observed by Vajda in his study about the philosophical sources of the latter (see Vajda 1949, 180). A more important case is that of the well-known Spanish Jewish author Judah Halevi (1085–1141). In his main Judaeo–Arabic work, the Book of the Khazar (in Hebrew, Sefer ha-Kuzari), an explicit defence of Judaism with respect to the other religions and to philosophy as well, he significantly employed Avicenna’s Epistle On the Soul (Risala fi l-nafs) as a direct and literal, albeit implicit source for his description of man’s soul in chapter 12 of book five, as definitively shown by David H. Baneth (see his introduction to Judah Halevi 1977). Also a more “mystical” work by Avicenna, Living Son of the Watchful (Hayy ibn Yaqzan), apparently inspired Abraham Ibn Ezra in writing his own work in Hebrew on the same subject, the Iggeret Hay ben Meqits (around 1150), as shown by Israel Levin (see Levin 1983).