The aim of this paper is to reframe the taxonomy debate which has, in recent years, come to dominate private law theory. We argue that the debate to date has been flawed by two fundamental mistakes. First, little attention has been paid to how legal taxonomies are actually used. This, we argue, is regrettable: how we build a taxonomy depends on why we build a taxonomy, and a clearer focus on this question produces an approach that is very different from the approaches that currently dominate private law theory. Secondly, both sides in the debate have misunderstood what legal concepts are, and hence tend to misuse them. We argue that legal concepts are Weberian ideal types, and use philosophical theories of concepts to put forward a very different understanding of how concepts acquire content and are used in the legal system. Putting these together, we argue for a far more developmental, and historically informed, approach to taxonomy and to legal concepts generally.