David Bentley Hart, a skeptic about the uses of natural law in our pluralistic society, writes:
Assume that we can establish the existence of a moral imperative implicit in the orderliness of the world, as perceived by a rational will that, for itself, must seek the good: Does that assure that we can prove what hierarchy of values follows from this, or how we should calculate the relative preponderance of diverse moral ends? Yes, we may all agree that murder is worse than rudeness; but beyond the most rudimentary level of ethical deliberation, pure logic proves insufficient as a guide to which ends truly command our primary obedience, and our arguments become ever more dependent upon prior evaluations and preferences that, as far as philosophy can discern, are culturally or psychologically contingent. Consistent natural law cases can be made for or against slavery, for example, or for or against capital punishment, depending on which values one has privileged at a level too elementary for philosophy to adjudicate. At some crucial point, natural law argument, pressed to disclose its principles, dissolves into sheer assertion.
To anyone who creates “a false dilemma by imagining a real division between the discrete realms of supernatural and natural knowledge,” Hart responds:
What we call “nature” is merely one mode of the disclosure of the “supernatural,” and natural reason merely one mode of revelation, and philosophy merely one (feeble) mode of reason’s ascent into the light of God. Nowhere, not even in the sciences, does there exist a “purely natural” realm of knowledge. To encounter the world is to encounter its being, which is gratuitously imparted to it from beyond the sphere of natural causes, known within the medium of an intentional consciousness, irreducible to immanent processes, that grasps finite reality only by being oriented toward a horizon of transcendental ends (or, better, “divine names”). There is a seamless continuity between the sight of a rose and the mystic’s vision of God; the latter is in fact implicit in the former, and saturates it, and but for this supernatural surfeit nothing natural could come into thought.
It does not then represent some grave failure of natural reason that philosophy cannot achieve definitive moral demonstrations, or that true knowledge of the good is impossible without calling upon other modes of knowledge: the (ubiquitous) supernatural illumination of a conscience—a heart—upon which the law is written, Platonic anamnesis (of the eternal forms or of what your mother taught you), cultural traditions with all their gracious moments of religious awakening (Jewish, pagan, Christian, Hindu, Taoist, Buddhist, Muslim, Sikh, and so on), prayer, inspiration, the cultivation of personal holiness, love of the arts, and so on. There is no single master discourse here, for the good can be known only in being seen, before and beyond all words. Certain fundamental moral truths, for instance, may necessarily remain unintelligible to someone incapable of appreciating Bach’s fifth Unaccompanied Cello Suite. For some it may seem an outrageous notion that, rather than a collection of purportedly incontrovertible proofs, the correct rhetoric of moral truth consists in a richer but more unmasterable appeal to the full range of human capacities and senses, physical and spiritual. I, however, see it as rather glorious: a confirmation that our whole being, in all its dimensions, is a single gracious vocation out of nonexistence to the station of created gods.
– “Nature Loves to Hide” (First Things)