The ‘pragmatic maxim’ is basis of Pierce’s pragmatism. To form this maxim, Pierce was influenced by Descartes’s and Kant’s ideas – especially Descartes’s term of ‘clearness’ and Kant’s interpretation of “Pragma”. At first step, Pierce defined clearness from Descartes’s and Leibniz’s points of view; however, he found these points of view insufficient and criticized them. After that, he presented his own pragmatic maxim and introduced this maxim as the highest level of clearness. In order to give a name to this maxim, Pierce selected the term of ‘Pragma’ (instead of ‘practice’), because - based on Kant’s view - ‘experience’ absolutely interferes in the meaning of pragma. The pragmatic maxim, is a logical maxim that was outlined in Pierce’s ‘research theory’ and it is focused on a sensible practical effect created after every theory. In research theory, Pierce discussed ‘opinion’ as it makes the human ready to act. According to Pierce’s discussion, the task of human’s thought is ‘to create habit’, and the identity of habit is ‘to direct into action’. As a result, Pierce made a connection between opinion, action, habit, and sensible and practical effects of opinion. The Pragmatic maxim is also a semantic maxim and its main functions are clearing the metaphysics’ dilemmas and clarifying that some of its terms are meaningless.