Reflecting upon the ongoing conversation with Feser, Hart, and others, I remembered my own little essay on natural law. It does have one simple mistake: I didn’t really explain Aquinas’ taxonomy of laws correctly. Otherwise, I do think it gets to the basic issues. The “old” natural law position does not deny the religious nature of reality, but it does allow for objective reason.
In fact, in some ways natural law is itself “presuppositionalist.” It just says that everyone presupposes the same things, and that they must do so in order to exist in the universe which God created. This is very different from saying that they must know that they presuppose this, or that they must necessarily live consistently with it. The fact that they do and always will do so is enough for social and political matters.
Natural law is also very helpful for evangelism. As the financial investment commercial puts it, “Even kids know it’s wrong….” The relevant question isn’t whether this is true; it’s why. Christians should not basically agree with Nietzsche (or Cormac McCarthy, for that matter!), but rather they should point to him as an example of where natural law’s opposition must invariably lead. Since that option is intolerable and unworkable, natural law must be the case. And since natural law is the case, natural law’s dependent foundation, theism, must also be the case. This alone will not get a person saved, but it is, as the older theologians called it, the preamble to faith. It starts the person moving down the trail which will only end in Christ.
None of this supposes that the job can be done apart from the Holy Spirit. Some Calvinists misunderstand this point, assuming that rationality is somehow “Arminian.” But if that were the case, then it wouldn’t only be true regarding evangelism, but rather everywhere. We would need to not try to think or act until first moved (or until we found a Scripture reference – but then how we would know how to read it?), and that would create the wildest sort of enthusiasm. Such a criticism is actually not Reformed at all, but rather Anabaptist. Instead, the Reformed have been supremely confident in reason and creation, because they know that it is itself already theonomous, infused with God’s goodness in virtue of its created nature.