Paul DeHart: "Reason and Will in Natural Law"
Theories of natural law are divided into two kinds. The first kind grounds moral obligation in reasonableness. Actions that are substantively or non-instrumentally reasonable or good are, just for that reason, taken to be obligatory. The second kind grounds morality in the will or command of some person (or persons) with the authority or power to command. In theistic versions of will (or command) based morality, God is the authoritative or power person in question. On such a view of morality, some act is good or right just because commanded by the relevant person (or persons) and wrong only insofar as forbidden by that person (or persons). It is sometimes suggested that the first view, commonly referred to as the intellectualism, is Catholic and the second view, commonly called voluntarism, is the Protestant view. Both views of moral obligation (and so theories of natural law grounded in each view) are unsound.
This typology for accounts of obligation and for theories of natural law is problematic for two main reasons. First, the dichotomy is a false one. It is possible to construct, as William of Ockham did, a divine command theory of natural law that is ultimately voluntaristic, on the one hand, and in which divine commands, grounded in nothing but omnipotent power, are nevertheless promulgated through right reason which in no case fails, on the other. Indeed, a morally unconstrained, omnipotent deity could create a world in which actions are right or wrong depending on their reasonableness (or conformity to the requirements of reasons) and in which the requirements of right pertained the proper function of human persons. Thus, it seems that there is a broadly logical possibility of a theory of natural law that is voluntaristic, rationalist, and teleological. The intellectualist-voluntarist dichotomy fails to recognize this. The dichotomy fails because it does not go all the way down to the deep ontology of moral obligation.
Second, each account of moral obligation described above fails, philosophically, in important ways. Ethical voluntarism as such is self-referentially incoherent. Consequently, the divine command variety of ethical voluntarism is also self-referentially incoherent. Moreover, the divine command variety of ethical voluntarism that is rationalist and teleological is also self-referentially incoherent. The intellectualist account of moral obligation fails because such an account is a non sequitur. Just because some act is good or reasonable it does not follow (analytically or otherwise) that the act in question is prescribed (i.e., morally mandatory). For an act to be obligatory, it must not only be good or reasonable but also prescribed. What intellectualist accounts of moral obligation and natural law leave out is prescription. So doing, the intellectualist leaves out a necessary condition of obligation.
In view of the foregoing, I suggest that moral obligation is a compound rather than a simple property. Given the self-referential incoherency of voluntarism, reasonableness (or goodness) is a necessary but not sufficient condition of moral obligation. Given the non sequitur committed by the intellectualists account of moral obligation, the good or reasonable action that is obligatory must be prescribed—which is to say, it must be willed or commanded by an authoritative person (or persons). The compound nature of moral obligation in turn points to the necessity of a lawgiver. But it also points to the necessity of a lawgiver who is and whose commands are substantively good.