What is the relevance of historical, and in particular genealogical, investigations for projects of conceptual engineering? I address this question by bringing together two prominent authors in each of these traditions: Foucault for genealogy, and Carnap for conceptual engineering. I argue that Foucaultian genealogy is a suitable approach to address a specific lacuna in Carnap's articulation of explication, namely, insufficient attention for the preliminary stage of clarifying the explicandum. Moreover, the focus on practices in Foucaultian genealogies facilitates a reflection on the functions of the concept to be explicated, which is crucial for the fruitfulness of the explication as a whole. I start by canvassing a number of commonalities between Carnap and Foucault, as they were both influenced by Kant and Nietzsche; they shared a number of philosophical commitments such as a rejection of metaphysics and a tolerant meta-normative stance. I then discuss the lacuna in Carnapian explication, and argue that Foucaultian genealogy provides the right level of detail to remedy this lacuna. I close with a discussion of a concrete example, the concept of marriage, and conclude that this combination of Carnapian explication with Foucaultian genealogy is an illustration of the relevance of historical analysis for conceptual engineering.
