I thank Joe Carter for noticing an essay of mine on Two Bases of Morality in Catholic Theology originally published in Dappled Things , and I thank both Joe and the various others for taking the time to comment on that essay. Before I respond to those comments, let me provide a little background.
In contemporary academic philosophy, there are three main kinds of moral theory. There is virtue theory or eudaimonism, which is the way the Greeks thought about morality and which is nowadays associated with Aristotle. There is utilitarianism, which was invented in the modern period and is associated with Bentham and Mill, although it has roots in Hume. And there is deontology, which was also invented in the modern period and which received its classic expression in Kant.
Thus, Rosalind Hursthouse begins her important book On Virtue Ethics by stating, Virtue Ethics is a term of art, initially introduced to distinguish an approach in normative ethics which emphasizes the virtues, or moral character, in contrast to an approach which emphasizes duties or rules (deontology) or one which emphasizes consequences of actions (utilitarianism). Almost every contemporary introduction to philosophical ethics repeats this classification. See, for example, Anthony Kennys A New History of Western Philosophy . This is such standard stuff nowadays that if you type deontology into Google and then continue with the letter u, Google will suggest deontology utilitarianism virtue theory as a possible search for you.
So, when I distinguished Aristotelian virtue theory from Kantian deontology in my essay, I was just repeating a truism of contemporary philosophy. My only original contribution was pointing out that some Catholic moral theologians incorporate concepts from both systems, apparently without realizing that these systems are widely understood to be incompatible. Virtually no one working in philosophical ethics would think that such mixing and matching was a viable strategy.
Thus, the answer to Joe as to why theology cannot use both kinds of concepts simultaneously is that theology, like any other rational discipline, has to be internally consistent. It is not a question of nuance, as Joe puts it, but a question of glaring self-contradiction. In virtue theory, an action is morally right or wrong depending on whether it is appropriately related to the human end (e.g., Summa Theologiae , Ia-IIae.18.1-11 ); in Kantianism, an action is right or wrong entirely independently of the human end (e.g., Groundwork for the Metaphysics of Morals , 4:395 ). It simply cant be both ways. You cant be a free marketeer and a socialist in economics, you cant be a nominalist and a realist in metaphysics, and you cant be an Aristotelian and a Kantian in morals.
Joe suggests that Christianity has long believed that human beings have dignity because they were created in the image and likeness of God. Christians of all stripes say this nowadays, but the idea has virtually no basis in the history of Christianity. Certainly the Fathers of the Church do not say such things. The reason is that the concept of dignity as a foundational moral concept was one they didnt have.
I havent checked every reference to Genesis 1:26-27 in the Fathers, but just now I did check every reference in Jurgens three volumes of The Faith of the Early Fathers , and not one of these is even about morality, much less an attempt to found morality on dignity and the imago Dei . Only in the modern era, when Christians borrowed the idea of human dignity as a foundational moral concept from the broader culture, has the imago Dei been pressed into service to ground morality.
This brings me to the Friend of Robert T. Miller who says that Dignitas is used a couple of hundred times in the Summae and by it Aquinas means the special worth of creatures who possess the excellence of rational mastery of their own acts. I appreciate the writers friendship, but this is not close to true.
According to the Index Thomisticus , dignitas and its various forms appear 343 times the Summa Theologiae , and I have looked at every one of these passages. In the vast majority of them, Aquinas is referring to the dignity of kings, bishops, priests, teachers, sacraments, virtues, human faculties, gifts of the Holy Spirit, the Eucharist, Christ, the Blessed Virgin, or various other things (see, e.g., Summa Theologiae IIa-IIae.102.1-2 , which is typical), but almost never to the dignity of persons as such.
The few references to the dignity of persons as such are concentrated in the articles on the Trinitarian persons and the articles on the person of Christ. They have nothing to do with Aquinass moral theory based on the final end for man elaborated in the Prima Secundae , and, moreover, none of these references speak of anything like rational mastery over [ones own] acts. Indeed, in one of the few places where Aquinas does speak of the dignity of human beings as such ( Summa Theologiae III.4.1 ), he expressly explains human dignity in terms of the final end for man, noting that human nature is naturally fit for ( nata est ) knowing and loving God, which, of course, is the final end for man in Aquinas.
My friend has fallen victim, I think, to certain contemporary authors who have adopted basically Kantian moral notions but want to claim the patronage of St. Thomas. His own texts support no such claims.