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Abstract. — What is the relevance of historical investigations for projects of conceptual engineering? In this paper, I address this question by bringing together two prominent authors in each of these two ‘traditions’: Michel Foucault for genealogy, and Rudolf Carnap for conceptual engineering. I argue that Foucaultian genealogy is a suitable approach to address a specific and important lacuna in Carnap’s own articulation of explication, namely the all-too-brief engagement with the preliminary stage of clarifying the explicandum. I start by canvassing a number of commonalities between Carnap and Foucault, in particular the fact that they were both heavily influenced by Kant and Nietzsche, and that they share a number of philosophical commitments such as an anti-metaphysics stance and a deflationist meta-normative stance. I then discuss the clarification lacuna in Carnapian explication, and argue that Foucaultian genealogy provides the right level of detail to remedy this lacuna. I close with a brief 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.