Somewhere behind Feser’s argument slouches the specter of what is often called “two-tier Thomism”: a philosophical sect notable in part for the particularly impermeable partitions it erects between nature and grace, or nature and supernature, or natural reason and revelation, or philosophy and theology (and so on). To its adherents, it is the solution to the contradictions of modernity. To those of a more “integralist” bent (like me), it is a neo-scholastic deformation of Christian metaphysics that, far from offering an alternative to secular reason, is one of its chief theological accomplices. It also produces an approach to moral philosophy that must ultimately fail.
Before completing that thought, however, it might help to rehearse just a few of the conceptual obstacles our age erects in the path of natural law theory. So:
First. Finality’s fortuity. Most traditional accounts of natural law require a picture of nature as governed by final causality: For every substance, there are logically prior ends””proximate, remote, or transcendent””that guide its existence and unite it to the greater totality of a single cosmic, physical, moral, social continuum embraced within the providential finality of the divine. They assume, then, that from the “is” of a thing legitimate conclusions regarding its “ought” can be discerned, because nature herself””through her evident forms””instructs us in the elements of moral fulfillment. In our age, however, final causality is a concept confined within an ever more beleaguered and porous intellectual redoubt. One can easily enough demonstrate the reality of finality within nature, but modern scientific culture refuses to view it as in any sense a cause rather than the accidental consequence of an immanent material process….