Lon Fuller’s account of the “internal morality of law” is sometimes described as a kind of “merely procedural natural law theory.” But Fuller also held that “the most important respect in which an observance of the demands of legal morality can serve the broader aims of human life generally” is something that “lies in the view of man implicit in the internal morality of law.” (p. 162. All quotations are from Fuller, The Morality of Law, Revised Ed. 1969.) Fuller explains that “[t]o embark on the enterprise of subjecting human conduct to the governance of rules involves of necessity a commitment to the view that man is, or can become, a responsible agent, capable of understanding following rules, an answerable for his defaults.” (p. 162) This is the set-up for the excerpt that follows:

Every departure from the principles of the law’s inner morality is an affront to man’s dignity as a responsible agent. To judge his actions by unpublished or retrospective laws, or to order him to do an act that is impossible, is to convey to him your indifference to his powers of self-determination. Conversely, when the view is accepted that man is incapable of responsible action, legal morality loses its reason for being. To judge his actions by unpublished or retrospective laws is no longer an affront, for there is nothing left to affront—indeed, even the verb ‘to judge’ becomes itself incongruous in this context; we no longer judge a man, we act upon him. (pp. 162-63) …

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The whole body of law is permeated by two recurring standards of decision: fault and intent. Philosophic discussion of these notions has largely concentrated on their role in the criminal law, where they have given rise to the most abstruse arguments, including that concerning freedom of the will. But these twin standards play an equally important role in the law of contracts, torts, and property. Examined closely they turn out to be difficult and elusive conceptions in whatever area of the law they appear. Yet without them we would have no thread to guide us through the labyrinth. When one of them fails, we are apt to reach for the closest approximation of it. When there is no clearly determined intent, we ask what intention the parties would have had had they foreseen the situation that has arisen. When neither party seems chargeable directly with fault, we ask which of them had the best chance to prevent the harm—which, in other words, as closest to being at fault. (p. 167)

Notice what happens when these two tests, and their near relatives, fail completely. This occurs in the law of contracts when performance of an agreement is hampered or its significance is changed by some external event, such as the cancellation of a coronation procession. In the law of property our familiar standards fail when nature intervenes and takes control, as when a river shifts its course, removing twenty acres from A’s land and adding twenty-five to B’s. In cases like these the litigants do not appear as responsible agents, but as the helpless victims of outside forces. We can no longer ask: Who was to blame? What did they intend? Since our usual standards of justice fail us, we are at a loss to know what justice requires. If we were to lose throughout the law the view of man as a responsible center of action, all legal problems would become like those I have just suggested. (p. 167)