ABSTRACT
This chapter recourses the philosophical literature on common sense and on universal rationality. It constitutes a refinement of the notion of common practice. The actions to be included under the term 'common practice' are only a small subset of those the author usually associate with everyday life for normal people under normal conditions. The best starting point for describing common practice is probably to investigate its links to common sense. Specialised practices, like the practice of dealing with cloud-chambers in all its complexity, include many more actions than are included in common practice. Since common practice underlies common sense, it seems reasonable to attempt to gain some insights into what such common practice must include by taking a closer look at common sense. The role of biology in the elaboration of the concept of common practice, however, together with the role of other empirical judgements, must be handled with care.
