You might find this interesting:

I told Clayton Cramer in an email that I believed that the Constitution’s text was sacrosanct and that it and the Declaration of Independence contained principles that were “objective, ascertainable, and timeless.” Although I didn’t so elaborate, I believe those principles are generally rights to life, liberty, equality, the pursuit of happiness, and property. Some of the notable particular principles/rights—I can’t list all of them because they are literally unenumerable—include “conscience,” “speech,” and “contract.”

He replied:

Objective, ascertainable, timeless principles--why, if you weren't an atheist, you would be sounding downright Christian! This is the core conflict going on in our society right now, between a Platonic notion of universals, and an Aristolean view that is skeptical.

My reply back illustrates my own philosophy and how I think it dovetails with the philosophy of the founding:

I’m not an atheist—rather I’m somewhere between Deism & Agnosticism. I believe in objective truth and operate in the tradition of the Enlightenment—or the tradition of objective notions of Reason—which has its origins in Ancient Greece, had its heyday in the Enlightenment and is exemplified in the modern era by folks like Ayn Rand. I know she was an atheist. And most of our founders weren’t (I don’t think any were avowed atheists). But the belief primacy of Man’s Reason over Biblical Revelation, I would argue, was dominant among the most influential framers. They believed in God and were heavily influence by the Deistic-Unitarian philosophy which holds that the existence of God is ascertainable by Man’s Reason, that He created us with unalienable rights (this is not a Christian doctrine—even though many Christian’s adopted this idea). Susan Jacoby in her book Freethinkers, A History of American Secularism describes how God & Reason co-exist according to Enlightenment founding principles:

What did distinguish the most important revolutionary leaders was a particularly adaptable combination of political and religious beliefs, constantly subject to revision in an era when modern views of nature, science, and man’s place in the universe were beginning to take shape. These views included skepticism vis-à-vis the more rigid authoritarian religious sects of their day; the conviction, rooted in Enlightenment philosophy, that if God exists, he created human rationality as the supreme instrument for understanding and mastering the natural world; and the assignment of faith to the sphere of individual conscience rather than public duty. The logical extension of such beliefs was a civil government based not on the laws of God, as promulgated by self-appointed earthly spokesman, but on the rights of man. p. 14.

Now many in the day believed that orthodox Christianity was perfectly “Reasonable” and thus there was no conflict (which is what Locke argued in “The Reasonableness of Christianity). Others like Jefferson—and even Adams—scrapped much of such faith because it was “unreasonable,” (i.e. the Trinity). It appears based on Adams’s writings that even though he was quite conservative, that he put his faith in Reason over Revelation. Here is a letter of his to Jefferson in 1813 commenting on Britain’s repeal of a statute that made it a crime to deny the existence of the Holy Trinity:

We can never be so certain of any Prophecy, or the fulfillment of any Prophecy; or any miracle, or the design of any miracle as We are, from the revelation of nature i.e. natures God that two and two are equal to four. Miracles or Prophecies might frighten Us out of our Witts; might scare us to death; might include Us to lie, to say that we believe that 2 and 2 makes 5. But We should not believe it. We should know the contrary. Id at 13.

Now this Enlightenment philosophy holds religion to be a matter of “opinion” which government has no business touching or ruling over. But the principles of natural law/rights—principles ascertainable from Man’s Reason, unaided by Biblical Revelation—are within the realm of “knowledge,” not “opinion.” And these principles are what founds the public institutions of our nation—not the Bible.

I don’t follow the ACLU’s interpretation of “separation of Church & State.” I support vouchers and have no problem with public proclamations of a generic non-denominational God. And I realize that not every founder was so Gung-Ho imbibed in the Enlightenment. I think it would make for an interesting law-review article—maybe I’ll try to write it one day—that examines the Enlightenment, i.e. Madisonian, Jeffersonian vision of separation of Church & State and how it differs from both the ACLU’s version and the conservative version that holds that “disestablishment” means no government established sect only, whether state or federal.

[Update] Timothy Sandefur and Ed Brayton have commented on this post. Thanks for the link guys!