If seen as just a change in citation practice, this might be at best an interesting shift in the form of judicial opinions. But these changes do not merely reflect a transformation in citation practice. They embody a change in what counts as a legal source, and thus in what counts as a legal argument; and what counts as a legal argument-as opposed to a moral, religious, economic, or political one-is the principal component in determining just what law is. The boundaries of law are set by the boundaries of legal authority, and law speaks as law through its sources. When previously prohibited authorities become optional, and when previously optional authorities become mandatory, the nature of legal sources has changed, and with that change comes a transformation in the nature of law itself.

Unknown, Frederick Schauer - Thinkin…, loc. 153