Law is not morality. The is isn't ought. Don't say an immoral law isn't a law because it is and you know it. Just say the law is immoral.
Other things positivists say that aren't related to the above but may be related to why the aforementioned above may not be getting through to you, you and your many adroit feelings:
1) Studying the vocabulary of law and legal concepts is as important to our understanding of law as historical and social studies. Incidentally words, like the law, don't have a specific moral orientation.
2) The imperative theory of law: Law is command. (As it would if, for example, you (I'mma call you "natural law theorist"and Nawath for short) got your way and law was treated as inseparable from morality. That would be some kind of Power Rangers fusing type situation and pretty damn imperative. If you keep them separate, you get to retain your moral voice which means it's your power ranger and the law's power ranger.) (Hart hates this one because he's got a lot riding on his Rule of Recognition theory, designed to prove that a legal system isn't a simple matter of command aka the government aren't a band of robbers/Gunmans Writ LARRRGE)
Okay so just because these two claims are admittedly WEAK doesn't mean the claim that law is separate from law isn't true.
YOU, Nawath, might possibly get it twisted because you think the problem with #2 is that it's lacking a moral aspect. Then you go "Aha! These positivists are totally ignoring morality. I can tell because Thing Positivists say #2 is soooo obviously inadequate." NO Nawath! DON'T BE CONFUSED. The missing part is actually the portion of law related to law-making procedure for legislators/lawmakers so that all these little peoples can know what the actual rules are that they have to obey. Also in a democracy, the sovereign mega-boss is composed of a regularly changing cast of rowdies from the public--this means the public is the commander is "law is command" would basically mean "Do whatever" and democracies don't work like that. We. Must. Have. A. Procedure.
What's that I hear? Do I hear you muttering about a dimly sensed yet urgent albeit blurred criticism of the command theory that involves and important connection between law and morals? I see. I see how it is. You are talking about the portion of law that gives you, ordinary citizen, private power ranger, the ability to make some legal dealings with your fellows--contracts, wills and trusts AKA "the REALIZATION OF WISHES AND CHOICES." This does not seem to be some kind of a command.
Yeah.
This guy, Salmond, thought of that. BUT THEN HE ALSO GOT IT TWISTED. He concluded that the best way of explaining wish-granting wheelindeelin authority conferring law is some sort of necessary connection between law and morality. I say to him, rules that confer rights don't have to be moral. Rules and like laws. Mayyybe they go hang at morality's house sometimes. Das cool. But they don't friggen live there. They live at their own house. And sometimes they go visit the house of the DARKEST EVIL. And then morality won't speak with them for months or punches them in the nose or something. Point is. You get the point.
Now let's go and see these Americans and what they've got to say about some nonsense about some combination law and morality. You know what they say, these so-called Realists? Core and Penumbra.
Core=the written law, plain and simple, easily applicable to garden variety cases
Penumbra= Weeeeird unusual unforeseen cases that seem pretty related to an already existing law it's going to require some judicial stretching. (Bonus part of the text: toy car says, "I am a vehicle for the purpose of this law." Rollerblades hastily chorus (chorus! sometimes they even finish each others'----sentences!) "We are not a vehicle." Hart calls the toy car and the rollerblades "dumb"thus silencing their point of view for the remainder of the paper.)
In ambiguity we need JUDICIAL DISCRETION. Ah, Nawath, so predictable, so tender. You think judicial discretion involves reference to morality, elsewise the judge is some kind of heartless android, ill-suited for the profession. You are wrong. You know why? it's because you think "ought" signifies always some sort of movement toward goodness. But if we're in an evil system, the law ought to ensure the greatest amount of evil. So what actually happens is the judge makes a decision weight the societal consequences against the wording of the law and just chooses something they think fits. I'm not trying to pretend law is complete. (So you don't try to pretend a deliberate manipulation of the sense of the law to suit some sort of societal goal is any more logical than a deliberately close-minded narrow headed literalism because it isn't.)
CUTTING TO THE JUICY BIT AKA NUREMBERG TRIALS DISCUSSION
I, Hart, can understand why people would be pretty concerned with morality and its position relative legality. But what they should have done is been candid about the handling of the trials--basically they decided to go with the lesser of two evils and sacrifice a distaste for retrospective law in favour of punishing heinous crimes. They did not not do this. The Nazi laws were laws at the time, however reprehensible, and definitely, if those persons moral consciences had been in good working order, they would have realized that they had a duty to abstain from following the law BUT that is exaclty where the separation between law and morality is key. In fact, this is a perfect example of an instance where law and morality are in fact polar opposites.
Okay, Nawath? Get it straight.