Drawing on philosophical studies seems to be a common practice among researchers specializing in public law, particularly in constitutional law. Since the constitution decides (or serves as a basis to decide) on the fundamental political issues in a State, it is often argued that the understanding of such issues requires to examine its foundations, thus leading our research into the field of philosophy. But how do we discern which philosophical works or doctrines are relevant for our research? And with which methodological tools do we face these philosophical studies? The purpose of the paper is to reflect on these questions, with special emphasis on the way in which constitutional scholarship draws upon works on philosophical concepts that also happen to be constitutional terms. To do so, I use the notion of human dignity as a “case study”, in order to illustrate the meaning and possible implications of these reflections by reference to a specific concept.