Ethical beauty and indecency, which belong to the optional activities of human beings are the sources of issuance of ethical commands and prohibitions have been a matter of discussion from a long time ago, and philosophers of ethics have made discussions specially on the quality and source of them and have expressed some views in this regard. Allame Sayyed Mohammad Hossein Tabatabai, a great contemporary philosopher, has also expressed his view which is new in some respects. His theory involves, in the present writer's point of view, two main parts. The first part deals with the quality of existence of ethical beauty and indecency which are mental assumptions. The second part deals with the source of ethical beauty and indecency which depends on the assumption of necessity and exigency, with its three branches: necessity of doing, necessity of necessity, itself, to be the basis of the assumptions of beauty and indecency is the main aim of the present article which will be discussed in light of Allamah's views.