The argument of this page fits in three lines:
Law is based on morality.
Morality is objective.
Therefore law is objective.
The previous page showed that morality is objective. This page shows why law has to rest on morality, and why that settles the question of where law comes from.
Why law has to rest on morality
Suppose someone tells you that law doesn't need to be based on morality. Then it isn't based on morality. And if it isn't, no one has any moral obligation to obey it.
Go one step further. If law were to contradict morality, we would have a moral obligation after all: to resist it, and to dismantle the institutions that enforce it.
No society can hold together on those terms, and every government knows it. Whether a given government actually has moral authority is debatable. But every government claims to have it, and claims that its legal system rests on it. Its entire ability to govern depends on that claim, and on enough people believing it. A government that openly admitted its laws had no moral basis would be unheard of, and it would not last a week.
So every government that claims the authority to govern, which is to say every one of them, rests that claim on its laws being moral.
Conceding the debate
This is why "law doesn't have to be moral" is not a position anyone can actually defend. The moment you say it, you have conceded the whole debate.
If your law has no moral basis, no one owes it any respect. What remains is the law of the jungle. And under the law of the jungle, as soon as someone else gathers enough raw force to overthrow your system and smash it to pieces, they are perfectly justified in doing so, because by your own admission morality never entered into it. All that's left is brute force and the appetites of the powerful.
Democracy is no exception
"But we don't have a king. We have a democracy."
Democracy rests on the same thing: raw power, only in larger numbers. Instead of one man making the law, it's many. The idea is identical. A king claims to create law by issuing it from his throne. A legislature claims to create it by issuing it from a great marble building.
Both use verbal rituals. The king's herald cries, "Hear ye, hear ye!" The legislature announces, "The ayes have it!"
Both use ceremonial objects. The herald blows a trumpet. The Speaker bangs a little wooden hammer.
In both cases the ritual has one purpose: to hide the fact that not one person in the room has any more power to edit the law than a mathematician has to edit the Pythagorean theorem.
Internal validity, not external authority
There are two ways something could claim to be law.
Man-made rules rest on external authority. A statute is "law" because some recognized body enacted it. Its validity comes from who said it.
Natural law rests on internal coherence. A principle is law only if it can be derived, by valid reasoning, from true premises about reality, about human beings, and about what harms and what sustains life. Its validity comes from whether it is true.
That second standard is much harder to meet, and that's the point. Saying "this is natural law" proves nothing by itself. The claim stands only if the argument is sound and the premises are true, exactly as in mathematics. Which is why a civilization founded on natural law depends on its people caring, seriously, whether their arguments are valid and their premises honest.
Law is found, not made
A civilization that understood this would be built very differently from ours.
- Law would be found, not made. The bodies that work with law would behave less like parliaments and more like scientific or mathematical communities, where claims are tested, challenged, and refined in the open.
- Legitimacy would be a matter of truth before procedure. A rule wouldn't be legitimate because it "passed." It would be legitimate because it can be shown, by reasoning anyone can check, to match the moral structure that was already there.
- Every person would be a co-inquirer, not a subject. Each of us would have both the right and the responsibility to reason about the law ourselves, the same way anyone, in principle, can check a mathematical proof.
No outside source is needed for this. A free mind, reasoning honestly, has access to the same law that any expert claims to see. No one has privileged access to natural law that isn't equally open to you.
The only part of morality that may be enforced
"Fine, morality is objective. But law and morality are two different things. Morality might be built into reality, but law is man-made."
They are different, but not in the way the objection supposes. Morality covers everything about how to live well: kindness, honesty, generosity, courage. Law is narrower. It is the part of morality that answers a single question: when is force justified?
That is what separates a law from a piece of good advice. A law is something that may be enforced. And whether force against another person is justified is itself a moral question, among the most serious there are. It does not become less objective because it is enforced. It becomes more important to get right.
So law isn't something separate from morality, invented by people and laid over the top of it. Law is morality's answer to the question of force. And if morality is objective, so is that answer.
Which leaves one conclusion. A rule that contradicts that answer, a rule that uses force where force is not justified, or forbids defense where defense is justified, cannot be law, no matter who wrote it.