This article analyzes the unsystematic character of Arendt and Foucault, which, far from denoting a lack of rigor, stands as a particular form of research that takes the form of a laboratory of thought in both are like "seismographs" who, at the combining philosophical reflection with historical analysis, they detect, on the one hand, concepts that, from being used so much by tradition, become exhausted and disused and, on the other, they capture fragiles points both in our harmful custom and in our ways of thinking, act and feel. To bring the above to fruition: first, two prejudices that can be raised against Arendt and Foucault and that are the result of the particular styles of research of these authors is examined. Then, both the unsystematic mode and the historical, specific and contingent mode with which Arendt and Foucault undertake their respective inquiries are addressed in separate topics, which is reflected in the "separation and fine-tuned discrimination" of concepts and problems addressed by them. Finally, the issue of truth is formulated in both, as well as the unique way in whom they approach it: in Arendt the truth linked to personal responsibility and in Foucault articulated with the production of subjectivity.