Tasnim interpretation, by utilizing various methods of interpretation based on sources of interpretation, has a comprehensive ijtihadic interpretation method. In this comprehensive method, one of the methods is interpretation with reason or rational interpretation. In his valuable interpretation of Tasnim, Ayatollah Javadi Amoli, by focusing on comprehensive ijtihadic interpretation, has focused on rational interpretation and has made extensive use of argumentative reason. From his perspective, reason plays the role of a “source” in this position, and rational interpretation is in fact the opposite of the narrational and apocryphal method. The epistemological result of applying argumentative reason and a source in interpretation is not only to confirm the Quranic teachings and to show the harmony of the Quran with reason and rationality in revealed teachings, but beyond that, to further explain and deepen the understanding of the teachings and also to avoid incorrect or incomplete and superficial understanding. The present article, written using a descriptive-analytical method, explains the nature of reason, demonstrative reason, and comprehensive ijtihadic interpretation, and mentions various perspectives on interpretation with reason, and explains some of its Quranic and narrational evidence. The important point in this topic is to pay attention to the principles of using demonstrative reason in interpretation. Demonstrative reason has several applications in interpretation, some of the most important of which are: the role of demonstrative reason as a common ground and negation of meaning, the role of demonstrative reason as a specific ground and determination of meaning, explaining the contents and deepening understanding, confirming and strengthening the contents of the verse, general assignment and absolute restriction, and criticism of the interpretation of interpretive narrations.