This contribution proposes an epistemological view of the development of a typology for qualitative comparison. The operations undertaken in the context of European research on providing care to children from single-parent families in five European countries provide a guiding principle for the analysis. The theory defended here is that the typology results from a projection of traits exemplified in cases. The typological construction is justified if we assume, in a Weberian, nominalistic interpretation, the unreality of the resulting representations. The construction of a typology for policy takers makes it possible to identify the relevant variables without first postulating the coherence of national models. It is not a matter here of directly analyzing public action itself as a mechanism, but of analyzing it indirectly through its uses, as a combination of selected resources.