How much can individual be influenced by reason? In his review of ethics and language, Charles L. Stevenson, in the Saturday Review, Stuart Chase states " This is one of the most important questions ever asked, one on which our survival may depend.In deed, the reason and rationality concept play a crucial role in our individual and social life so that the survival of our civilization, namely, our social, educational and moral system, as Chase says, may depend on this question. On this base, the question is concerned, amongst the others, with the place and weight of reason is one's theory of understanding and action (social action, political action, educational action and even moral and religious action). So many attempts have been done to find out the answer but it seems that these attempts have been stranded, and this is because philosophers and those who are working to expose the matter disagree about the nature of reason and rationality. They may view the concept reason and rationality differently, and thus their theories on action and understanding, which they may give, based on these views would be unlike. In this article, I will be concerned with concept rationality and reason in order to work out and classify some major aspects of reason on which we may reach to some extent to a reasonable conclusion and increase agreement over the matter. These aspects, or questions with which theories of reason, in different ways are concerned, are as follows: Reason as a human mental faculty; Reason and its ability to move people to act; as an instrument or as a source of knowledge; Reason or reasons. On this base, by referring to Ayer and Moor, I will show that not only emotivists and intuitionists, but also those who have entitled their theories as " rational" like Toulmin (1960, 1979), R.S. Peters, George D Snell (1988), B Gert (1973), D. Guathier (1986, 1990, 1991), who maintain that reason occupies the essential place in the sphere of action and also in the process of decision making in that sphere, like morality and making moral judgment, do not argue for the same theory. This is because they do not have the same theory of reason. After all, I will give an Islamic view concerning rationality based on which we can declare the weight of reason in decision making and performing an action, and will give us a better conception of an Islamic educated person