While using court decisions as legal precedents and case law are central to Western law, the importance of the institution of fatawa (non-binding answers by Islamic legal scholars to legal questions) has been called "central to the development" of Islamic jurisprudence. This is in part because of a "vacuum" in the other source of Islamic law, "qada`" (legal rulings by state appointed Islamic judges) after the fall of the last caliphate the Ottoman Empire. While the practice in Islam dates back to the time of Muhammad, according to at least one source (Muhammad El-Gamal), it is "modeled after the Roman system of "responsa"," and gives the questioner "decisive primary-mover advantage in choosing he question and its wording."