Abstract: Functionalists, especially those inspired by American Legal Realism, downplay the importance of abstract concepts and their interrelations in legal reasoning. Hence, they stress shallow, narrow, and isolated concepts, in order to be close to the facts in a transparent way. In this paper, we address an often-overlooked function of law: managing legal concepts themselves. That is, one aspect of law is partially self-referential. Various devices involved in legal reasoning are designed to make the system of legal concepts work better, from fine-tuning the results of the use of concepts to tinkering with the concepts themselves. This requires us to look at law as a system, but one that is both inward-looking and operating on itself, and, at the same time, concerned with how law operates in the real world. Law also uses various devices to manage the system of concepts, and these devices in turn serve various functions. These functions include maintenance, modulation, and modification of concepts, depending on the actual or potential misfiring of the concepts in question. As we will suggest, this offers deeper insight into the role that legal fictions, equity, and presumptions play in the law.