There are several extensive reviews of the development of relations [Bloom, Tinker MargulisBloom 1993,Gentner RattermannGentner Rattermann1991,Gentner, Rattermann, Markman KotovskyGentner 1995,SmithSmith1989]. We do not attempt to duplicate these reviews here. Instead, we highlight five facts about development, facts about which there is remarkably little dispute in the usually contentious subfield of cognitive development. We take these as the facts that must be explained in an account of how and out of what relations are made.