The Harvard legal theorist, Lon Fuller (1902-78), and the Oxford legal theorist, H.L.A. Hart (1907-), were undeniably the English-speaking world's most respected and influential legal theorists from the 1950s through the 1970s, and their influence persists today. Robert Summers (1984: 2) calls Fuller the “greatest proceduralist in the history of legal theory, ” and ranks him as one of the four most important American legal theorists of the past 100 years, the other three being Oliver Wendell Holmes, Roscoe Pound, and Karl Llewellyn (1984: 1). Indeed, in 1948 Fuller succeeded Pound in the Carter Professorship of General Jurisprudence, after nearly a decade on the faculty at Harvard Law School. Aside from The Morality of Law (1964/1969), Fuller is best remembered for his debates over legal positivism in the 1950s, first with Ernest Nagel (see chapter 5, note 2), and then Hart. The latter exchange “was perhaps the most interesting and illuminating exchange of views on basic issues of legal theory to appear in English in this century” (Summers 1984: 10).

It is important to point out, however, that in the great debate over legal formalism and legal realism that raged in the United States in the 1930s, this future “greatest proceduralist” took the side of legal formalism's critics. Unlike the legal realists of his day who were advising legal scholars to describe judges' behavior as such, however, the young Fuller emphasized the importance of studying the reasons judges offer for their decisions and behavior.