Habermas' and Foucault's approaches have many similarities and they share basic commitment to the project of freedom. Where they disagree is how to justify this project. For Habermas this requires proving non contingency of the project of freedom because he thinks that without this one cannot claim universal validity for such a project. For Foucault however the project is essentially contingent. However, this doesn't make the project less important or less dignified. Within this broader context, Habermas' and Foucault's respective projects take different shapes. True to his intent Habermas' whole project can be seen as trying to develop a theory of rationality (broadly construed in both theoretical and practical senses) from philosophical as well as sociological angles, from synchronic as well as diachronic viewpoints. Foucault on the other hand is more "practical." He takes our essential task to be not so much "seeking to make possible a metaphysics that has finally become a science" but rather "to give new impetus, as far and wide as possible, to the undefined work of freedom." The task is to make possible the real exercise of freedom. This is a practical task and a difficult task. Archeology and genealogy are tools for making this difficult and precarious work of freedom possible. The project of freedom cannot rely on metaphysical or scientific certainties, nor on the promise of utopias. The only guarantee of freedom is freedom itself.
cross posted at Foucauldian Reflections