Different viewpoints upon the nature of ethical necessities has become the source of variety in theories in this regard. One of these them is Ayatollah Larijani’s theory of Ethical Necessities which has been distinguished from other theories due to having belief in meaningfulness and nafs ul-amri realities. Explaining Ayatollah Larijani’s viewpoint and having an overview of the other theories from his viewpoint, the theory of ethical and rational necessities has been analyzed and evaluated in three areas of semantics, ontology, and epistemology and while certainty of different parts of this theory is insisted on without any conflicts, it is addressed by some criticisms. Restraint of reason in perception shall be reflected upon and Quranic, narrative and philosophical emphasizes about the position of practical reason and its necessity and policy shall be considered. In accordance with the position of reason in different resources and explain it precisely, our perception from rational commandments demands more explications and by considering the approach reasonableness of intellect, the implied justifications of the above-mentioned viewpoint will be faced to some conflicts. However, if the position of reason is realized differently, investigations of the scientists including Professor Larijani’s on the theory of ethical and rational necessities will become the commence of acceleration in the process of achieving a comprehensive theory about ethical theory of Islam.