This article proposes a reflection on the question of the principles of analysis and construction of concepts in the social sciences based on the metaphor of ”family resemblances” proposed by Ludwig Wittgenstein. This image – which emphasizes the idea of partial similarities rather than that of necessary and sufficient conditions – proves to be particularly useful for reflecting on the process of the construction of objects , as well as on the development of concepts in the social sciences. Stressing the existence of a tension between the wide open character of social reality and the work of “temporary closure” in which researchers are engaged, the image of family resemblances reminds us that the construction of objects and concepts always implies a deal of arbitrariness, but that it should not be confused with forms of free interpretation: researchers can find criteria, both formal and empirical , which, although fragile and temporary, can be used for the collective validation of concepts.