Saadya Gaon (882 – 942), one of the outstanding Rabbis in the period of the Geonim, rejected the legitimacy of legal inference, as part of his polemics with his contemporary Karaite scholars. The paper analyzes Saadya's stance regarding the logical basis of legal inference, and shows that Saadya's distinction between reason and revelation in the domain of legal inference is only in regard to the ‘illah– the factor that connects the case with its law. The rationality of the commandments, on the other hand, is based according to Saadya upon the manfa‘ah– the utility of the commandments, and hence Saadya's religious doctrine turns out to be coherent and consistent. Maimonides (1138–1204), who was one of the most important figures in the Jewish scholarly world in the Middle Ages, adopted the Aristotelian concept of dialectics in order to facilitate his theory of Jewish legal argumentation. Unlike Saadya, Maimonides saw inferences in the realm of the law as legitimate. His position can be considered an inclination towards the Karaite ideology according to which reason must be the ruler in the realm of the law. Nevertheless, Maimonides' stance deviates from that of Karaites in a crucial point: according to Maimonides, only authorized institutions are qualified to use legal inference. Since the Talmud, according to Maimonides, represents the teachings of the rabbinical authorized institutions, its legal instructions must be followed. The article describes Maimonides' position regarding legal and Talmudic inferences, and shows that Maimonides' inclination towards the Karaite theory remains within the limits of the Rabbanite ideology.