J.P. Moreland argues that traditional theism is the best explanation for the truth of ethical nonnaturalism in the broad sense, a correspondence theory of moral truth, and the falsity of ethical egoism.[1]

Definitions

non-natural property: an attribute that is not a scientific, physical characteristic of physics or chemistry (e.g., being a C fiber, having negative charge, being magnetic).[2]

Moreland’s Argument Formulated

We may represent Moreland’s argument with the following structure:

(1) Irreducible, nonnatural value properties do exist and are a part of the furniture of the universe.

(2) The truth of moral propositions is determined by correspondence with moral facts.

(3) We have moral obligations that seem to require duties that often go against our own best interests.

(4) The best available explanation of (1)-(3) is that God exists.

(5) Therefore, God exists. 

Moreland’s Defense of (1)

Moreland defends (1) by appealing to “our common sense moral intuitions.”[3] He writes:

Similarly, consider the claims “Kindness is a virtue;” “Humans have value;” “Persons have value.”  Or, as Roderick Chisholm says, “Mercy as such is good.”  In spite of what Nielsen says, these are synthetic a priori propositions, where at least on the surface, it seems like just as “Red is a color” commits one to the existence of red and color, “Kindness is a virtue” commits one to the existence of kindness and virtue. … “Mercy as such is good” commits one to non-natural properties that do exist and are part of the furniture of the universe.[4]

Although in one instance Moreland defines the term ‘non-natural’ in a way implicitly compatible with the term’s broad sense (and hence moral facts and properties could be either supernatural or sui generis),[5] in several other instances he refers to irreducible moral properties.[6]  Hence, nonnaturalism in the narrow sense is the position with which he seems to most sympathize and in effect endorses.