Since Islamic shari‘ah (law) is for all muslims at all times and in all places, it provides for every Muslim all the legal rules regarding whether an act is obligatory, forbidden, disliked, recommended or permissible, which he needs in order to obtain his real salvation. Since the Qur’an and the Sunnah of the Prophet do not deal with all the individual rulings in a very specific and detailed way and contain mostly general rulings, ijtihâd, i.e. a total expenditure of effort in the seeking of an opinion regarding a rule of divine law, is often needed. According to B. G. Weiss, “since the law of God comprehends, in principle, the whole of life, it must be continually expounded as novel life situations present themselves. Consequently, the existence of ijtihâd is not a right but a responsibility, one that rests in every age upon the community as a whole.” However one of the controversial problems in ijtihâd is that of takhti’ah (fallibilism; admission of the possibility of error in the judgments of the jurist, mujtahid) and taswib (infallibilism; maintenance of the jurist’s infallibility and denial of any possibility of error). In other words, there is a question whether jurists holding conflicting opinions can all be said to be above error. Muslim thinking on this issue is truly divided. There are two completely different opinions. Shi‘ah scholars and a number of Sunni scholars admit the possibility of error in the fatwas of the jurists and accordingly they are called, “mukhatti’ah (derived from khata’, error), whereas a majority of Sunni scholars believe that the mujtahids are above error, and hence refer to them as musawwibah (derived from sawâb). In this paper I intend to consider briefly the concept, definition, and types of ijtihâd and then examine briefly the criteria and justification of takhti’ah and taswib according to both Shi‘a and Sunni scholars. I will also try to present the arguments of both sides in the issue.