Approximately four decades have elapsed since the Islamic government was established in Iran. Nowadays one of the most important topics of discussion in which the Islamic government and the legislature are involved is the degree and kind of affinity between the Islamic government and the society’s established custom. No doubt, discussions on the extent to which the Islamic precepts and rulings are related to the established custom of society makes it a jurisprudential and juridical necessity to bring fixed and changing rulings up for discussion. The reason for this necessity lies in the fixed and changing needs of human beings. One of the contemporary thinkers who fully realized the significance of ‘time and place’ in the realm of religion was Shahid MurtiÃÁ MuÔahhari whose concerns for these matters appeared in a collection of issues raised under the title of “Islam and the Exigencies of the Age”. In this research work the criterion of affinity between the fixed and changing rulings have been investigated from MuÔahhari’s viewpoint and concerning the concept ‘fixed’ and ‘changing’ some relevant cases from among his works have been scrutinized. Among these criteria one can refer to the idea of paying attention to the progress and development in Islamic societies, putting emphasis on the common interests, and considering the spirit of the Islamic Law (shariÝah). Having conducted the research, a conclusion has been drawn that a review of Shahid MuÔahhari’s thought reveals the fact that accepting the exigencies of the age and attending the fixed and changing criteria in drawing up Islamic laws will be the solution to the problems in the field of ‘authorized interpretation (ijtihad)’and expertise (fiqÁha) in the legal, social and political realms of the Islamic government.