SUBJECT AND OBJECTIVES : Religious rules in Shiite jurisprudence are inferred from the four sources of the Quran, Sunnah, reason and consensus; but in addition to these sources, some foundations such as common law are also mentioned. Based on it, the question arises here “what are the roles of common law and Ertekazat in common law in understanding and inferring the religious rules? This article seeks to answer this question and tries to study and analyze the functions of common law in understanding and inferring the religious rules. The research hypothesis is that common law and Ertekazat in common law are used in understanding the words of religious arguments, subjecting and de-subjecting of common law for the religious documents, proving or denying some rights and other issues that are used by jurists and lawyers in the process of inferencing. METHOD AND FINDING : The research method is descriptive-analytical. One of the findings of the present study is that most scholars of the Islamic jurisprudence and law have not distinguished between these two foundations; but it is more correct that common law is considered from the category of objective matter in the practical life of people, but Ertekazat in common law are from the category of subjective matter. CONCLUSION : Presence of custom in the scene of inference causes the contemporary Muslim to realize that the religious rulings are made according to the customary understanding, facts and tangible needs, and therefore in his spiritual biology more obedience to the rulings, commands. He will have the divine and the spiritual program of Islam and his spirituality will be strengthened.
