Karaite scholar; lived at the end of the eleventh, or at the beginning of the twelfth, century. Two decisions of his have been preserved by Hadassi. The first of these ("Eshkol ha-Kofer," alphabet 197) refers to the eating of quail in the wilderness, which, according to his calculation, began on the 24th of Iyyar in the second year after the Exodus, and ended on the 24th of Siwan (Numbers 10:11,33; 11:18,19). The second decision ("Eshkol ha-Kofer," alphabet 236) refers to the conditions under which it was allowable to sacrifice outside the sanctuary. Isaac is also quoted by Jacob Tamani and the author of "Ḥilluḳ." Nothing is known of his literary activity.