When I gave a brief summary of my view of Natural Law a few weeks ago, I think one of the most important things I said was that Natural Law is good insofar as it refers to a law (or ethic) that exists independent of positive law (and on which positive law must be based) and is applicable to all persons of all cultures at all times. The reason why this is agreeable is because we Reformed Christians identify this natural law as being synonymous with the Moral Law expressed, for example, in the Ten Commandments. And it is this Moral Law that is ever binding on the human race.
Now, the other important thing I said was that this Natural Law is only agreeable as a whole if the means by which we know this ethical standard is the propositional revelation of God. That is to say, if one is claiming that we can know the precepts or rules in some other way, I cannot agree with this formulation. However, the fact that some natural lawyer claims that murder is wrong on the basis of some other standard of authority than the Bible, does not make the claim itself wrong. It is an important aspect of logical coherence that the proposition itself has truth content, even in the justification for the proposition is faulty.
For example, I believe that the God of the Bible exists. I believe this because the Bible says he does. The Bible is the authority in my worldview which determines whether or not God exists. This makes me a presuppositionalist. Other people agree with this same statement on the basis that they are convinced that their “scientific evidence” proves the existence of God. The two arguments (presuppositional and evidential) cannot both be equally epistemologically defensible because either the authority of God determines how we ought to interpret “scientific evidence,” or else this “evidence” determines (authorizes) the existence of God. Which has the final authority? God or evidence? One argument is deficient.
However, the proposition that God exists is true even if one uses a poor argument in its defense. It would literally be irrational to say that God’s existence depends on the goodness of our argument for it. This leads to postmodernism where what is a true proposition for some is not true for others.
In the same way, we can agree with the natural lawyer that murder is wrong even if we disagree with his argumentation on behalf of that proposition. Murray Rothbard had an entire system of political ethics which included the ideas that murder was wrong, theft was wrong, fraud was wrong, assault was wrong, and so forth. In all this we concur. And we appreciate and agree with Rothbard especially in light of the fact that he and his Thomist natural law were declaring war on the moral relativism, the utilitarianism, and the neoliberalism of his contemporaries. But we disagree with his assumption that Thomism was the best defense of these very rules.
Ethics are natural in the sense that they are not artificially created by human beings. They are known by reading the Bible’s propositions and by deducing from those propositions. But when some secular Natural Lawyer comes to the same conclusions as us, we may choose to challenge his argument (and this is part of Christian apologetics), but we are free to agree with his conclusion.
We may categorically affirm a type of natural law by virtue of its definition, especially when it is juxtaposed to positive law (which I talked about here), even if we challenge the way in which its conclusions are commonly justified. We may categorically affirm the conclusions of Rothbardian natural law, even if we challenge the way in which those conclusions are justified. The natural lawyer is right to say that murder, theft, fraud, assault, rape, and all those other things are wrong. But why are they wrong?
This is where we must emphasize the Christian view of morality, which attributes to God the authority to determine what is right and what is wrong. This is also where we differentiate ourselves from the so-called NL2K camp, which does not agree that Scripture binds n0n-Christians. I expressed my own view that 2K theology is good, but the “NL” part is not (according to their definitions), in this post.
The Christian worldview is not required in order for one to have rights or to agree with some ethical rule. But the Christian worldview is indeed required for one to intellectually justify both rights and ethics.