This paper discusses the social changes in the modern world, citing two institutional phenomena occurring today: the Third Sector and the Fourth Power. To discuss clearly, this research uses a new epistemological view, so that the complexity of the changes are fully understood. The Cartesian rationality has also been used by many social scientists, but - really - this linear thinking is unable to produce a complete understanding, seeing that society is multidimensional rather than unidimensional. Although the Cartesian rationality is useful for the natural and mathematical sciences, the dialogical of Morin and the double hermeneutic of Giddens are most effective for social studies. Finally, this research uses a new rationality to explain the birth of the Third Sector and the emergence of the Fourth Power.
Modern Society, Epistemology, Third Sector, Fourth Power.