Michael Martin and Paul Copan on morality
A long time ago, there was an exchange between Paul Copan and Michael Martin on morality, the moral argument for God, the divine command theory, Euthyphro's dilemma, etc. I remember it being really interesting and educational, so I thought I'd provide links to the article in the order in which they were written, not just for you, but for me, too, so I don't have to use google if I want to find them all again. :-)
"Atheism, Christian Theism, and Rape" by Michael Martin
"Can Micahel Martin Be a Moral Realist?" by Paul Copan
"Copan's Critique of Atheistic Objective Morality" by Michael Martin
"Atheistic Goodness Revisited: A Personal Reply to Michael Martin" by Paul Copan
"The Naturalistic Fallacy and Other Mistaken Arguments of Paul Copan" by Michael Martin
As far as I know, Paul Copan never responded to Michael Martin's last article, but I did find this short interaction with Martin's last article:
Atheist Michael Martin admits to this admixture [that man is both a sinner and a saint]; within the space of two paragraphs that humans both “seem so ungod-like” and are superior to animals in “intelligence, advanced linguistic and artistic capabilities,” possessing “mathematical, scientific, and technological knowledge.”8
Fn 8: Michael Martin, “A Response to Paul Copan’s Critique of Atheistic Objective Morality,” Philosophia Christi, 2 (2000): 75-90. I reply to Martin’s mistake in “Atheistic Goodness Revisited: A Personal Reply to Michael Martin” Philosophia Christi, Series 2, Vol. 2 (2000): 91-104. For some strange reason, in a later on-line essay, Martin persists in accusing me of a “contradiction” he himself espouses (humans as a mixed bag of goodness and evil) and that I had already addressed in my response to him (“The Naturalistic Fallacy and Other Mistaken Arguments of Paul Copan” : http://www.infidels.org/library/modern/michael_martin/copan.html). Martin’s obvious error is failing to distinguish between essential and accidental properties. Thomas V. Morris puts it this way: “There are properties which happen to be common to members of a natural kind, and which may even be universal to all members of that kind, without being essential to membership in the kind” (Our Idea of God [Downers Grove, Ill.: InterVarsity Press, 1991], 164). On the differences between essential and accidental, see Alvin Plantinga, The Nature of Necessity (Oxford: Clarendon, 1974).
That's all I could find. Paul Copan has written a few things since then on this same subject, though. There's a list of his articles here, some of which are on the subject of grounding morality.