Once an exact knowledge of the facts and conditions has been established, and the finest possible description of the conducts carried out, the question of the interpretation and significance of the actions then comes to the fore. This article proposes to show which are the generally implicit or non-thematized resources to which the sociologist then appeals. Going back to insights offered by two founders of comprehensive sociology, the author shows, that recourse is made on one side to the knowledge of a socialized being, to a psychology of convention, to rules of experiment (Simmel) and on the other side to a nomologic knowledge of usual ways of behaving (Weber).