Determining the origin of moral judgment is one of the main concerns of moral philosophers. Some Western thinkers have considered the collective agreement as a criterion of value and a basis for establishing moral rules. In Islamic thought, the fundamentalists have also used the rule of reason through jurisprudential inferences. In view of these apparent relationships, the present research has decided to deal with the feasibility of establishing or discovering moral judgments based on the basis of reason in the view of the Usulites, using a descriptive-analytical method. The findings showed that although some insist on the inherent validity and the impossibility of rejecting rational constructs, their arguments lack the necessary strength. More importantly, the application of the foundation of reason in discovering moral rules faces theoretical and methodological difficulties. Among these difficulties, the distinction between the nature of validity and validity in rational structures compared to moral values, the differentiation of the ontology of value in comparison with the context of rational structures, and the restrictive nature of values ​​versus rationality or rationality. It is rational.