Fuller disagrees with Hart about the separation of law and morality. We talked about three of his points.
Fuller noted that Hart’s rule of recognition replaced Austin’s sovereign. But, he reasoned, without enforced commands, there’s nothing to make legal rules mandatory. That would only work if the legal rules are also moral: they can only gain respect and deference if they are good (p. 642).
I think Hart would have said that legal rules are mandatory in the same way that any rules are. The rules of baseball are mandatory: if you want to score, you have to run in a particular way. But no one thinks the rules of baseball are merged with morality.
Fuller, it seems to me, believed that we have higher aspirations for law than that. We want people to think it’s important to comply with the law and we want officials in the legal system to strive to get the law right. We don’t want ordinary citizens or officials to think of laws as just a set of rules. Here are a few expressions of his point of view.
“with Professor Hart’s paper … It is now explicitly acknowledged on both sides that one of the chief issues is how we can best define and serve the ideal of fidelity to law. Law, as something deserving loyalty, must represent a human achievement; it cannot be a simple fiat of power or a repetitive pattern discernible in the behavior of state officials. The respect we owe to human laws must surely be something different from the respect we accord to the law of gravitation. If laws, even bad laws, have a claim to our respect, then law must represent some general direction of human effort that we can understand and describe, and that we can approve in principle even at a moment when it seems to us to miss its mark.” (Fuller, 632.)
“No written constitution can be self-executing. To be effective it requires not merely the respectful deference we show for ordinary legal enactments, but that willing convergence of effort we give to moral principles in which we have an active belief. … to be effective a written constitution must be accepted, at least provisionally, not just as law, but as good law.” (Fuller, 642.)
I think that in saying we have an “ideal” of “fidelity to law,” Fuller means that real law has to be worthy of respect, loyalty, and faithfulness. So a putative law that we have an obligation to oppose wouldn’t meet the ideal: it would not be worthy of respect, loyalty, and faithfulness.
Hart, on the other hand, thinks we would be better off if we saw laws for what he thinks they are, namely, a set of rules, invented by people for their own purposes. They are an important set of rules because they deal with important matters; in that way, they’re different from the rules of baseball. But, at bottom, they’re just rules. So, in his opinion, we would think more clearly if we did not mix our ideal laws with what he regards as the real ones.
Fuller pointed out a variety of conditions that laws have to meet in order to be effective. They have to be announced in advance, rather than retrospectively, for example, and they have to be regularly administered. In other words, running the legal system fairly in various ways seems to be a precondition of running it effectively. And that suggests a point where law and morality merge.
It seems to me that Hart largely agreed with him here. (See §V of Hart’s article.) Hart just pointed out that this involves a lot less than a full merger of law and morality. An effective legal system could have wicked laws, for instance.
Fuller, on the other hand, never said that the law had to incorporate all of morality. He did, however, think that a system such as that in Nazi Germany could violate the morality of order to such an extent that it no longer had laws (see pp. 660–61). Hart did not accept that.
So I think they ultimately disagreed with one another. But it is not easy to locate the point where their agreement becomes disagreement.
I think Fuller clearly got Hart wrong on one point. Fuller asserted that Hart suggested that “a retroactive criminal statute would have been the least objectionable solution to the problem” posed by the Nazi law case (Fuller, 649). But all Hart said was that retroactive legislation is the best alternative if you think the woman has to be punished. It’s a conditional point and I don’t see where Hart said the condition is met.
Here’s what Hart wrote, with some additions to make it clear.
The court of appeal to which the case ultimately came held that the wife was guilty of procuring the deprivation of her husband's liberty by denouncing him to the German courts, even though he had been sentenced by a court for having violated a statute, since, to quote the words of the court, the statute "was contrary to the sound conscience and sense of justice of all decent human beings." … The unqualified satisfaction with this result seems to me to be hysteria.  Many of us might applaud the objective - that of punishing a woman for an outrageously immoral act - but this was secured only by declaring a statute established since 1934 not to have the force of law, and at least the wisdom of this course must be doubted. There were, of course, two other choices.  One was to let the woman go unpunished; one can sympathize with and endorse the view that this might have been a bad thing to do.  The other was to face the fact that if the woman were to be punished it must be pursuant to the introduction of a frankly retrospective law and with a full consciousness of what was sacrificed in securing her punishment in this way. Odious as retrospective criminal legislation and punishment may be, to have pursued it openly in this case would at least have had the merits of candour. It would have made plain that in punishing the woman a choice had to be made between two evils, that of leaving her unpunished and that of sacrificing a very precious principle of morality endorsed by most legal systems. Surely if we have learned anything from the history of morals it is that the thing to do with a moral quandary is not to hide it. Like nettles, the occasions when life forces us to choose between the lesser of two evils must be grasped with the consciousness that they are what they are. (Hart, 619–620.)
To summarize, Hart thought there were three options.
Hart clearly rejected option 1 and he did not make a choice between 2 and 3. All I see is “if the woman were to be punished” then it has to be under option 3. Since Hart never said that he thought the woman should be punished, I think he meant to keep option 2 on the table. In fact, I think he chose his words very carefully to avoid stating a position.
Fuller, Lon L. 1958. “Positivism and Fidelity to Law: A Reply to Professor Hart.” Harvard Law Review 71 (4): 630–672. JSTOR
Hart, H. L. A. 1958. “Positivism and the Separation of Law and Morals.” Harvard Law Review 71 (4): 593–629. JSTOR