For the last 150 years, Canadian courts of general jurisdiction have exercised a special function. At the request of the executive, they issue advisory opinions in the absence of a live “case or controversy”. Borrowed from the 1833 Judicial Committee Act, but absent from the U.K. domestic context as well other Anglo-American systems, advisory opinions have been critical to Canadian jurisprudence and, in particular, to its constitutional law. They are so familiar that a basic tension at their core has become obscured. The tension arises from the asymmetry between references' formal and practical status. Formally, such opinions as “non-binding” – they do not provide independent reasons for compliance by other actors. In actual practice, though, they are treated as though they do. Drawing upon Chapter 9 of my book (forthcoming, Hart), the paper discusses what created and explains this tension, and what it can reveal about the nature of authority and about law as such.