Abstract : The Philosophy of Jürgen Habermas is one of the most famous in the 20th century. The researchers in communication studies are obviously very interested in his work. Habermas had to define his position in front of marxism in the same time of the USSR collapsed. He build an original thought between political philosophy, philosophy of language, knowledge psychology. His concept of "public space" is especially usefull in communication : how can we take a common and right decision, justified by our common values ?