The chronological paradox in customary international law (or, the virtue of sloppy timing in a messy world)

Customary international law suffers from a problem known as the "chronological paradox." The orthodox understanding seems to require a state belief a norm is the law (opinio ) for it to become law.; Existing approaches to the paradox violate either the law's created character or its normativity, because they share a commitment to a mentalistic/psychological and descriptive understanding of opinio.; We should understand opinio as a matter of language, rather than belief. Further, the rule language that constitutes opinio should not be understood descriptively but rather as a species of what Austin dubbed performatives. Together, these ideas let me analyze the opinio element as a matter of moves with a discursive practice. In assessing whether some rule-expression is warranted, we look at it the proprieties of the practice, not at an external realm of rules.; International legal discourse is flexible enough to allow rule change without paradox because it is a "messy" practice---one in which the propriety of moves is not fully determinate. There is not full convergence on proprieties amongst its participants, but so long as participants are committed to the practice, they will be able to give and demand reasons for and against particular uses of rule-expressions. A significant section of the essay is taken up in describing how such "messy" disputes can progress in customary law discourse, with particular reference to the debate over NATO's (putative) humanitarian intervention in Kosovo.; I resolve the paradox neither precisely by solving it nor by dissolving it. The idea that new norms must be rooted in old norms is retained, but in terms of justificatory appeal rather than in terms of belief. I shift terms of the question from "what norms are there?" to "what kinds of justifications can be provided for the use of particular norm-expressions?" The latter question, unlike the former, is answerable. Because of messiness in the practice, it will not often have an unequivocal answer, but by way of compensation, there will generally be a lot to say in those situations where the warrant of a rule-expression's use is in dispute.