How can philosophers determine when they should conclude their research process? This paper introduces the saturation principle to philosophical methodology. The idea of saturation, first formulated by Glaser and Strauss in 1967, has become an influential quality criterion for qualitative research in the hermeneutical and pragmatist traditions in the social sciences. By taking a pluralist and gradualist approach, this paper explores how different types of saturation may guide philosophers in deciding when to conclude their research activities. It identifies five core activities that are central to philosophical research projects and describes which type of saturation is most relevant to each of them. It also introduces two new forms of saturation: namely, perspectival and reflective saturation. While the paper concludes that saturation is a valuable methodological principle for philosophical research, it does not provide strict rules, let alone checklists. Saturation should be understood as a gradual process rather than one cut-off point.
