The issue of the source of ethical value is one of the most important issues in the field of metaethics. Moral philosophers have come up with different perspectives on this issue. Some Islamic thinkers, including Muhaqqiqi Isfahani, have considered the rationals` tradition as the formulating cause for moral propositions. This research is intended to emphasize on the viewpoint of Muhaqqiqi Isfahan and examine the role of rationals` tradition in formulating moral propositions critically. Although he emphasizes the conventionality of ethical propositions and their being formulated through the rationals` tradition, he believes that the rationals` opinions are issued on the basis of man's survival, interests and corruptions and is valid under certain conditions. The semantics of ethical concepts may not be permitted. Also, this viewpoint is not based on the correct reasons and is not the ultimate justification of the survival of man and his interests and corruptions.