This piece on Princeton's Robbie George inspired some thoughts on the natural law. The natural law is what man can know from his reason unassisted by revelation or other sorts of unargued dogma. The natural law is Capital T Truth, something non-negotiable, and True regardless of how many people do or don't believe in it. For instance, even if 99% of the population denied 2+2 = 4, they'd still be wrong.
Natural law is often associated with a religious point of view -- doctrinaire Catholicism, because the Church's teachings have embraced the natural law through Aquinas.
But Aquinas didn't "invent" this concept -- the Pagan philosopher Aristotle did. And Reason itself is not beholden to any Church's doctrine; rather it's supposed to be the other way around. As Allan Bloom wrote in The Closing of the American Mind, "Aristotle...was used as an authority almost on a level with the Church Fathers and was assimilated to them. This was, of course, an abuse of Aristotle, who thought that authority is the contrary of philosophy....The essence of philosophy is the abandonment of all authority in favor of individual human reason." pp. 252-3.
And indeed, Reason has as often been used to question rather than support traditional religious doctrines. The Enlightenment was one big natural law project in that it posited Man's Reason as the ultimate discerner of Truth. That doesn't mean Church doctrine or Revelation were, according to natural law, untrue. But rather, they had to be Reasonable in order to be True. So it was under the auspices of the natural law, not only was America Founded, but so too was the French Revolution conducted. And there we saw that Reason turned out to be not too friendly to the Catholic Church.
Now, in researching the philosophical origins of the Founding, I've dismissed the "Christian Nation" thesis entirely. The Declaration of Independence and the Constitution simply did not come from the Bible. The Founders were very clear that whatever Truth may be found in the Bible, it was not the guidebook from which our government was constructed. However, I do take natural law claims to the Founding seriously, because the United States's government was founded under the rubrics of "Reason" and "Nature."
As John Adams put it in "A Defence of the Constitutions of Government of the United States of America" [1787-1788]
"The United States of America have exhibited, perhaps, the first example of governments erected on the simple principles of nature; and if men are now sufficiently enlightened to disabuse themselves of artifice, imposture, hypocrisy, and superstition, they will consider this event as an era in their history. Although the detail of the formation of the American governments is at present little known or regarded either in Europe or in America, it may hereafter become an object of curiosity. It will never be pretended that any persons employed in that service had interviews with the gods, or were in any degree under the influence of Heaven, more than those at work upon ships or houses, or laboring in merchandise or agriculture; it will forever be acknowledged that these governments were contrived merely by the use of reason and the senses.
". . . Thirteen governments [of the original states] thus founded on the natural authority of the people alone, without a pretence of miracle or mystery, and which are destined to spread over the northern part of that whole quarter of the globe, are a great point gained in favor of the rights of mankind."
Political science, according to the Founders, was a form of natural science. The Declaration of Independence was a self-evident Truth as much as 2+2=4. The Founders no doubt due to the influence of Isaac Newton viewed "Nation Building" as part of the same system of "mechanical and mathematical foundations [that] served [the] grounding post for their scientific reasoning," in Jim Walker's words. (Gary North makes a similar point in this article.)
But how relevant is natural law to us today? After Carl Becker (who once famously said "to ask whether the natural rights philosophy of the Declaration of Independence is true or false, is essentially a meaningless question") it is assumed by many, perhaps most that the Founders were "wrong" in believing that the natural law of the Declaration was "True" like the principles of natural science and in refusing to distinguish between the two. As Charles Murray recently put it, the doctrine of natural rights "is not a falsifiable hypothesis."
Murray is right, I think, that the Declaration can't be proven like 2+2=4; but this doesn't mean the Declaration is not part of some larger metaphysical Truth. Whether the Declaration is ultimately True in an empirical and/or metaphysical sense is a question I leave open.
Another critique of natural law is, even if it is True, because people disagree over its content, the Declaration of Independence has no proper place whatsoever informing constitutional law. This is Justice Scalia's critique. He stated, (as a Catholic) he believes in the natural law. He just doesn't believe that nine lawyers on the Supreme Court are the final arbiters of what the natural law says.
While I disagree with Scalia on the natural law and its relationship to constitutional law (and I think so too would the Framers), he certainly is correct that people disagree over the contents of the natural law. For instance, the above article quotes Robbie George as believing:
"[T]he genitals of men and women are reproductive organs all of the time--even during periods of sterility," he writes. To curb sexual practices he views as immoral, including oral sex and masturbation (which he calls "bad" sex), George supports state laws banning sodomy, adultery and fornication.
This certainly looks nothing like the natural law in which I might believe.
Another interesting question: How relevant is a Thomistic view of the natural law to the Declaration of Independence? Robbie George, Hadley Arkes, and the Claremont Institute are notable for conflating the two theories. But in fairness, they would assert that the natural law is what the natural law is: The Declaration of Independence is part of it; so too are Aristotle and Thomas Aquinas.
Moreover, they seem to argue that 1) government has the right to enforce the natural law (even in its Thomistic sense) and 2) public policies which contradict (their understanding) of the natural law weaken America's natural law Foundation by contradicting the Declaration of Independence.
So for instance, Harry Jaffa might argue: 1) the Declaration of Independence derives from the natural law; 2) slavery violates the natural law and the Declaration; 3) sodomy violates the natural law; 4) moral approval of sodomy destroys our ability to make moral judgments under the natural law such that, "If then sodomy is not unnatural...then nothing is unnatural, and nothing (including the persecution of sodomites) is wrong." Jaffa would probably go so far as to assert: "Moral approval of homosexuality destroys the Declaration of Independence."
Claremont disproportionately focuses on the "sodomy" part of the natural law, but not so much on masturbation, oral sex, and contraception, and for good reason. Since much of the public holds an unfavorable view of homosexuality, Claremont's argument might resonate with them. However, should the Thomists argue something along the lines of "if we accept a teenager masturbating as natural, then the Declaration of Independence unravels and we can't even say, as a matter of moral certainly, slavery and genocide are wrong," most of the public would laugh this off as a self-evident absurdity.
Some other complicating factors for those who would conflate Thomism with the Declaration:
1) The Founders virtually never invoked Thomas Aquinas (at least in a positive sense). This is probably because Aquinas is indissolubly connected with the Catholic Church. And because of said Church's poor record on religious toleration, our Founders, if you've read what they've said about the Roman Church, were practically anti-Catholic bigots.
Still the Founders did invoke Locke and other philosophers who inherited a Anglican natural law tradition from Richard Hooker, which ultimately traces back to Aquinas and Aristotle.
2) Even the Thomists disagree on some issues. For instance, Jaffa has tried to give himself an "out" and argued that contraception between married couples is not unnatural (if you have time to read the entire link from which this passage was taken, you will see how far off his rocker Jaffa is on these sexual issues).
Chan writes that "contraception would be just as immoral as homosexuality since it frustrates the natural purpose of sex." I believe this view to be mistaken, although it is one easy to make, because it is how the Catholic Church has interpreted the natural law. According to Aristotle -- the fons et origo of all natural law teaching -- all the moral virtues must be exercised according to the dictates of prudence....Mr. Chan attributes to me the absurd opinion that "the most important thing about man's nature is his ability to perpetuate the species." Other species may fulfill their natural destiny by generation alone, but mankind seeks his end in and by the soul no less than by the body. One's duty to one's progeny only begins with the circumstances of birth. It is the nurture and, above all, the education of the young, that parents must undertake when they bring children into the world. If the resources available to the parents are such that they have to choose between failing in their duty to many, or fulfilling their duty to a few, choosing the latter course may indeed be prudent.
So here we begin to see how in using the same natural law premises, we come to different outcomes. Jaffa and the Church differ on whether contraception can be "natural." However....
3) Just as natural law arguments can be made on behalf of contraception, so too can they be made on behalf of homosexuality. Natural law is after all premised on an observation of nature and homosexuality clearly exists within both animal and human nature. When one observes a minority in nature that deviates from a general trend, one can either anathematize it as "unnatural" or simply view it as a natural variation, part of biological diversity. (See Andrew Sullivan's Virtually Normal, pp. 46-8).
Dr. David Mazel, though he doesn't believe in the natural law, engaged in a thought experiment on my blog, where he made a pretty convincing natural law case on behalf of homosexuality. An excerpt:
But again, wait. If there is not one common Human, but rather two forms of humans, why not more? Who's to say that we should not in fact be speaking, not of Man and Woman, but of Heterosexual Man and Heterosexual Woman, in order to distinguish them from those other forms, Gay Man and Lesbian?
Perhaps the essence of Gay Man is different from that of Heterosexual Man, and the essence of Lesbian different from that of Heterosexual Woman, just as the essence of Man differs from that of Woman. If so--and Feser has given us absolutely no reason why it might not be so--then it stands to reason that Gay Man and Lesbian--as well as those naughty organs, Gay Penis and Lesbian Clitoris--have been designed by their Creator toward rather different ends than Heterosexual Man and Heterosexual Woman. Who can say? Perhaps Feser can read the Mind of God, or perhaps the Pope can, but I cannot, and anyway I'm trying to proceed on the basis of reason rather than revelation.
If Gay Man and Lesbian are Forms of their own, then natural law tells us that the moral thing for gays and lesbians to do is to strive to realize their essence qua Gays and Lesbians. The immoral thing for them to do would be to frustrate that realization. BTW, that applies to straights as well--including, I will assume, Feser. It is immoral for Feser or anyone else to deliberately frustrate the ability of gays and lesbians to realize their essence as Gays and Lesbians. (Read the entire thing here.)
4) Not only did the Founders rarely if ever invoke Aquinas, they also rarely discussed issues of "natural sexuality." Rather, they spent most of their time explicating Hobbes's/Locke's "state of nature" teachings on government; though they did discuss how natural rights related to issues like slavery and religion. On slavery, the case was clear: Slavery violated the natural law, and in a sense, the Declaration spelled the eventual end of that inhumane institution, even as the Constitution preserved slavery's legality.
On religion, according to the most philosophically minded Founders, the Trinity violated the natural law. The Trinity was simply an irrational and unreasonable doctrine. As Abigail Adams put it in her May 4, 1816 letter to John Quincy Adams, "There is not any reasoning which can convince me, contrary to my senses, that three is one and one three." Remember, that the majority of people at the time may have thought otherwise is irrelevant to natural law issues. 2+2 = 4 irrespective of whether the population at large accepts it or not. And just as we could say that the Declaration of Independence spelled the eventual end for the institution of slavery, so too did Jefferson believe that the Declaration spelled the end for the institution of Trinitarian Christianity when he declared, in 1822, "I trust that there is not a young man now living in the US who will not die an Unitarian."
Now, of course, one can make a natural law argument in favor of the Trinity. The point of stressing these differences is to note that because we differ on the finer details of the natural law, it is not possible for government to justly enforce the natural law simpliciter. This is what Jefferson believed when he wrote, in Notes on the State of Virginia that "The legitimate powers of government extend to such acts only as are injurious to others."
Indeed, I would assert that our natural rights republic is structured such that we have the right to do what arguably violates the natural law. Whether the Trinity is unnatural or not is irrelevant given that the rights of conscience are unalienable; thus people have the absolute right to believe and proselytize for any religion, no matter how orthodox, unorthodox, irrational or bizarre. Jaffa et al., support the right to privacy and the Griswold holding, meaning that individuals have a natural right to do what arguably violates the natural law (use contraception).
Moreover, the natural law generally doesn't need a government to enforce it; rather it enforces itself. Government is only needed to protect individuals' natural rights. Indeed, the Declaration of Independence holds that men have an unalienable right to liberty in its broad and general sense. The Declaration seems to dictate that most of man's decisions, even if they end up violating the natural law, be left in the private sphere of society, that man, in his "pursuit of happiness," is guaranteed the right to figure out for himself what life best leads to human flourishing, even if he ultimately gets it wrong.