Oxford University Press
Most of the philosophical literature on vagueness starts with the identification of the term whose vagueness is at issue -- tall, short, night, day, bald, tadpole, etc. But in legal interpretation an additional problem arises, because it is not always obvious which term in a legal text, or even which legal text, is the operative one. H.L.A. Hart's idea of a rule of recognition conceptualizes the way in which some second-order rule is necessary to identify which first-order rule is applicable to some form of conduct, but it is often the case that the second-order rule itself exhibits various forms of vagueness. When that is so, vagueness appears as a distinct problem with important but often unrecognized implications.
Frederick Schauer, Second-Order Vagueness in the Law, in Vagueness and Law: Philosophical and Legal Perspectives, Oxford University Press, 177–188 (2016).