This article is the first in a series devoted to the study of a priori in law. It is part of the ANTECEDENT research project supported by a Chair of the Initiative of Excellence Université Côte d’Azur sponsored by the French government . The aim of the project is to revisit the law through its preunderstandings, leave behind the law only better to return to it, propose an “antecedent” theory of law and apply this theoretical reflection to major topical issues. It is based on the following general hypothesis: if a priori are everywhere, and if the law is capable of dealing with a priori, then the law is everywhere, and not just where we want to leave it. To begin the research, this first study takes stock of the vocabulary of a priori in and around the law.