In this project I attempt to answer some of the questions which were raised in two previous books: Rules, Norms and Decisions (CUP 1989) and The Status of Law in World Society (CUP 2014), and in the subsequent discussions they have engendered. Both works used »law« as a prism for understanding social and political action since the prevalent approaches in the field, as varied as they might be in regard to the research agenda or the methods, all seemed to share the epistemological conviction that a »theory of action« has to satisfy the criteria of »theory«. It was however my suspicion that such a view - particularly well-articulated in positivist approaches to social analysis - was not only distorting but that it left important features of praxis unexplored. The new project, entitled Praxis: On Acting and Knowing, takes off from the earlier two books by arguing that a serious engagement with »praxis« has to deconstruct the underlying metaphysical assumptions that privilege »theory« and do justice to the peculiarities of action. Action is taking place in real (irreversible) time and is characterized by contingency instead of necessity and universality, as the »theoretical« take presupposes. To that extent my analysis harks back to Aristotle but is actually more occasioned by the wonder why the idea of the »primacy« of theory for generating useful knowledge and understanding the social world persisted even after the old ontology of the »chain of being« was dislodged from its privileged position by the skeptics’ attack on the Cartesian quest for certainty. Thus, although the old ontological speculation was replaced by an epistemology that privileged the subject (rather than the object or the ideas), reason was again conceptualized as universal and a-historical (non-contingent), leaving the old privilege of a »timeless« theory in place. In this project, I use Hume as my pivot to look back on the classical attempts of prudential reasoning and try to understand from his vantage point the conventional and historical character of social orders. (Friedrich Kratochwil)