This is an old post of which I am proud. It discusses the irony that many of America's Protestant Founders (even and especially the "enlightened" ones) were suspicious of if not downright bigoted towards Roman Catholics. Yet, when these Protestants made their public arguments and invoked that "higher law" which governs us, they tended not to open their Bibles, but rather spoke in the language of "natural law," which is what man discovers from reason not scripture. And Catholics, mainly through Aquinas, are the ones responsible for incorporating such a pagan notion (natural law is pagan because it originated with that pagan philosopher Aristotle) into Western Christian society. Indeed, if John Locke truly did believe in natural law compatible with orthodox Christianity, then he absolutely owes a debt to Aquinas, because Hooker -- the natural law philosopher whom Locke invoked -- operated squarely in the tradition of Thomism and indeed was scolded by his fellow Protestants for sounding too Roman Catholic.
Yet, Locke's approach to the natural law looks different than both Aquinas' and Hooker's. For one, Locke incorporated Hobbes' wholly a-Biblical "state of nature" notion into his natural law teachings and indeed, made such central to his political philosophy. And Jefferson's and Madison's "understanding" of natural law/natural rights -- a tweaked version of Locke's -- was less seemingly "Christian," and more enlighted and rationalistic than Locke's.
Indeed, proponents of the "Christian America" thesis are fond of tracing the phrase "the laws of nature and nature's God" to Blackstone. He argued for the compatibility and cooperation of reason and revelation, and seemed to hold them at the same level as "higher law" which no man made positive law could contradict. Blackstone once said:
"Upon these two foundations, the law of nature and the law of revelation, depend all human laws; that is to say, no human laws should be suffered to contradict these."
A few things should be noted. First Blackstone, like our Founders, was a Lockean. Our Founders were more influenced by Locke than Blackstone and both our Founders' and Blackstone's ideas about the natural law and government trace to Locke. Second, Blackstone was a Tory, who believed in absolute parliamentary sovereignty and our Founders were American Whigs. The Declaration of Independence is, in many ways, an anti-Blackstonian document, since it argues for a right to revolt against Parliament, the exactly opposite of what Blackstone believed.
Most importantly, look at the exact language that Jefferson adopted in the Declaration. He could have invoked, after Blackstone, "the law of nature and the law of revelation," as that "higher law" which all man made positive law should conform. But he didn't. Instead he invoked "the Laws of Nature and of Nature's God," or "reason" and jettisoned “the law of revelation” or "scripture."
Our Founders were rational theists, that is they believed reason demonstrated the existence of a "Nature's God." But "Nature's God" is, first and foremost, what man can know of God's existence and attributes from "reason" and not scripture or faith. Nature's God may well be the God of the Bible, but only if reason so proves. To Adams, Jefferson, and Franklin -- the men who wrote the Declaration -- reason proved Nature's God to be unitarian not trinitarian in His attributes.
That’s why the Declaration arguably supports an Enlightenment or "theistic rationalist" worldview over an orthodox Christian one. Though perhaps, the Declaration, Constitution and other Founding documents, to which both orthodox and heterodox thinkers approved, can be viewed as a lowest-common-denominator compromise between the two systems of thought.
There was a "common language" that both the orthodox and heterodox did speak in -- a "lingua Franca" (as Tom Van Dyke put it) -- and that language was "nature" or "reason" not scripture. Thus, the Protestant notion of sola scriptura is completely anathema to our Founding Principles of public truths. That is, sola scriptura is fine for the Churches and private consciences. But when making public arguments, our Founders so believed, one must translate those convictions into the language of "nature" and "reason."
And this is why the arguments of the Catholic theocons better resonate with Founding Principles than those of Protestant "Christianists" do. Yet, I think, we must respect thinkers like Father Neuhaus and Robbie George for making such naturalistic arguments, because those argument can be answered or reasoned with (whereas bald appeals to scripture cannot).
Ed Feser, natural law thinker, recognizes this ability to translate but still defends bald appeals to scripture:
Now, some liberals might object that it is one thing for religious intellectuals to weigh in on matters of public policy, but quite another for redneck Bible thumpers to do so. Yet why should the educational level of a person supporting a particular policy matter to the evaluation of the policy itself? If a policy can be supported with serious arguments made by serious thinkers, what does it matter whether someone who is uneducated also supports it for less sophisticated reasons? Do liberals and secularists think twice about supporting their own favored policies simply because some uninformed and inarticulate rock star or Hollywood starlet might favor them too?
My answer: it is not the education level that matters; it's the way in which the point is argued. Not all arguments are to be taken seriously. If some inarticulate rock star had a political epiphany during an acid trip, I'd write it off as nonsense and wait until I heard the "serious argument" by the "serious thinker." Likewise, we should write off bald appeals to scripture by the Bible thumpers and the like, that is until folks like Robbie George and Gerard Bradley come forth with reason based arguments. And then they can be answered with reason based arguments.