Natural law, whatever its form, is an attempt to derive normative rules from the nature of things. In other words, an attempt to bridge the is-ought gap. The way things are, it is argued, implies certain things that humans should do.
Natural law doctrines vary widely in their particulars, but ultimately they are united by an epistemological claim that moral obligations are perspicuous. They have to be for the doctrines to do any work: people can know what they are supposed to do, and can be held morally responsible for not doing them.
This epistemological claim makes natural law doctrines uniquely susceptible to discredit simply by being a minority position. If moral obligations are indeed clearly derivable from the nature of things, why has everyone else gotten it wrong, and what guarantees that your derivation is correct?
I can think of four possible answers to this question:
- Normative claims are conditional. This is to rewrite any “thou shalt” with “if you want x, then thou shalt.” Really, all normative statements are implicitly of this form. But some have an unconditionally true condition. If you want happiness… well who doesn’t? It is the objects of these necessarily-true normative statements – the claims of what has intrinsic value – with which natural law is concerned, and to which the criticism applies.
- Everyone agrees on the main points of natural law and takes it for granted; the argument is at the margins. But natural law cannot pretend to be a positive science like linguistics, the goal of which is to make explicit the rules we all know implicitly in language. A linguist who finds a widespread syntactic idiosyncrasy will take it as data and try to explain it. A moral philosopher, on the other hand, who finds some widespread strange habit, will pass judgement on it based on his prior reasoning. This is the point of natural law. It makes judgements, not predictions, so disagreements cannot be adjudicated by prediction, as in a positive science. In fact, natural law purports to be itself that adjudicator, standing as evidence to a moral dispute much like an experiment would in a scientific dispute. But, quis iudicat ipsos iudices? What is left to adjudicate when the judge itself is in dispute? Naturally, this is unavoidable at the deepest level of epistemological discourse. But natural law, in attempting to be that externally valid adjudicator itself, ultimately proves self-defeating.
- Our believers are unique in some way. We have divine revelation. Our thinkers are systematically smarter than those of other sects. History has selected us as a vanguard. But whatever the distinction, isn’t the point of natural law to enable ethical discussion across such divides? What good is natural law if it isn’t ecumenical?
- Natural law is not perspicuous after all. If the moral obligations we derive from the nature of things are indeed as obscure as the existence of controversy suggests, are they really moral obligations? One will need a theory of culpable ignorance here. And again, if the majority of people are culpably ignorant, what guarantees that you aren’t the ignorant one? (the answer to which will be some sort of option 3)
No doubt there are other creative ways of getting around the problem. But for theistic natural law, unless one is willing to argue that humanity has undergone a radical moral darkening over the past few centuries, the decline of natural law philosophy appears, on its face, to be its own refutation. And as far as I can tell, no nontheistic variant has ever attained the critical mass necessary for anyone to call its conclusions self-evident. Such doctrines cannot exist comfortably as minorities. And now that the form of argument has fallen into general disfavor, barring a third Great Awakening (some exogenous moral mass-enlightenment?), it is unlikely that any will gain enough momentum to regain credibility in the future either.