The paper is a translation of the first part of the second chapter of the 1st volume of "Theory of Communicative Action" (1981) by J. Habermas, where author undertakes a critical revision of M. Weber's theory of rationalization. Taking Weber's works on the sociology of religion as starting point, Habermas makes a systematic reconstruction of the concept of rationality with which Weber describes basic features of occidental rationalism, and shows contradictions inherent in Weber's theory of rationalization. For Habermas, these contradictions are caused, first, by too narrow conceptualization by Weber of the theory of action (based on the idea of purposive rationality) and, second, by confusion of the theory of action and of the system theory.