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The 1958 debate between Lon Fuller and H.L.A. Hart in the pages of the Harvard Law Review is one of the landmarks of modern jurisprudence. Much of the debate was about the relative merits of Hart’s version of legal positivism and Fuller’s brand of natural law theory, but the debate also contained the memorable controversy over the fictional rule prohibiting vehicles from the park. Hart used the example to maintain that rules have a core of clear applications surrounded by a penumbra of uncertainty, but Fuller offered a counterexample to insist that the language of a rule, by itself, could never determine any legal outcome. At one level, therefore, the debate was about the relative importance of language and purpose in applying a general rule to a particular issue. At a deeper level, however, the debate was about the formality of law and about the possibility of varying commitments to formality in different legal systems. By examining this debate, and by largely removing it from the surrounding controversy over positivism and natural law, we can gain valuable insights about legal rules, legal interpretation, and the nature of legal language.

Lon Fuller, in his response to H.L.A. Hart’s 1958 Holmes Lecture and elsewhere, argued that principles of legality—formal principles requiring, for example, that laws be clear, general, and prospective—constitute the “internal morality of law.” This Article contends that Hart never offered a clear response. Fuller’s claim supposes that observance of the principles of legality is both fundamental to law and inherently moral. In different writings, Hart seems variously to affirm and to deny that legality is a necessary criterion for the existence of law. Likewise, he sometimes suggests and elsewhere scorns the idea that legality has moral significance. This Article proposes that Hart’s apparent inconsistency might actually reflect the complexity of the terms. Some degree of legality might be a prerequisite of law, while some failures of legality might not condemn it. Principles of legality might have contingent rather than inherent moral value, might have moral value that is severable from their legal value, or might have both positive and negative moral effect. The Article argues, furthermore, that even the conclusion Hart strains to avoid— that legality inevitably links morality and law—is compatible with Hart’s positivism and opens a promising field for positivist jurisprudence.

This Article offers a new reading of Hart’s classic Positivism and the Separation of Law and Morals by rethinking the form of positivism Hart was putting forward. Hart’s separationism was not principally intended as a speculative proposition about the conceptual distinctness of law and morality but as a practical maxim about the need to distinguish what the law is from what the law ought to be. Hart believed that legal interpreters must display truthfulness or veracity about the law, being candid about what it actually says and how far it goes, rather than gilding the content of the law by ascribing to it what one wishes it said. “Practical positivism,” as Professor Zipursky calls it, was Hart’s antidote to the approaches of legal realism and natural law theory gaining ascendancy in American legal theory in the 1950s. Despite all of their differences, both realists and natural law theorists like Fuller treated the task of saying what the law is as inviting decision makers to make the law what it ought to be—“practical perfectionism,” in Zipursky’s terminology. Hart’s great lecture asserted, above all, that practical positivism was superior to practical perfectionism. Drawing upon a variety of contemporary examples, the Article suggests that the practical perfectionism that concerned Hart in 1958 is alive and well today among both conservatives and progressives—on the bench, at the bar, and in the legal academy. Conversely, originalists, textualists, and pragmatic conceptualists are among today’s descendants of practical positivists. The last half of the Article sketches a contemporary defense of practical positivism, adapting a Legal Coherentist framework to bolster Hart’s work against Ronald Dworkin’s criticisms.