In the Constitutional Era, the confrontation of intellectual discourses around the concept of "law" became one of the most central issues. For Islamists such as Na'ini, legitimate law was law that was consistent with the principles of Islamic law. Sovereignty belonged to God, and the parliament had the right to legislate only within the framework of fixed Islamic rulings. In contrast, secularists and Western-oriented intellectuals such as Taghizadeh considered law to be derived from the will of the people and collective wisdom and emphasized national sovereignty. This confrontation ultimately led to a crisis of legitimacy in the drafting of the first constitution and its amendments. The main question is: "What were the nature, source of legitimacy, and limits of law in the thinking of Islamists and secularists in the Constitutional Era, and what were their common and different points?" The hypothesis of this analysis is answered in a descriptive-analytical manner: "Although both currents were in agreement on the need to limit tyranny and establish the rule of law, they were fundamentally in conflict with each other in the bases of legitimacy and the scope of law."