The arbitariness problem also does not arise in DM theory. That is because a will needs a
reason, but a motive is a reason. The will, according to Aquinas, always chooses “under
the aspect of good,” which means that reasons are not inherent in the will itself (1992, ST
I, ii, q. 1, art. 5, corpus). In contrast, motives provide not only the impetus to action, but
the reason for the action. If we know that God acts from a motive of love, there is no
need to look for a further reason for the act. On the other hand, a divine command
requires a reason, and if the reason is or includes fundamental divine motivational states
such as love, it follows that even DC theory needs to refer to God's motives to avoid the
consequence that moral properties are arbitrary and God himself is not good. This move
makes divine motives more basic than the divine will even in DC theory.
DM theory also has the theoretical advantage of providing a unitary theory of all
evaluative properties, divine as well as human. DC theory is most naturally interpreted as
an ethics of law, a divine deontological theory, wherein the content of the law is
promulgated by divine commands. God's own goodness and the rightness of God's own
acts, however, are not connected to divine commands because God does not give
commands to himself. In contrast, DM theory makes the features of the divine nature in
virtue of which God is morally good the foundation for the moral goodness of those same
features in creatures. Both divine and human goodness are explained in terms of good
motives, and the goodness of human motives is derived from the goodness of the divine
motives.
An advantage of DM theory for the Christian philosopher is that it shows the importance
of Christology for ethics, whereas DC theory ignores the doctrines of the Trinity and the
Incarnation, focusing on the will of the Creator-God as the source of moral value. For
those who prefer virtue ethics to deontological ethics, the theory also has the advantage
of being a form of virtue theory. The basic moral concept is not law, but the good.
There are innumerable ways that a moral theory can be structured with a theological
foundation. The dominance of DC theory and natural law theory in Western religious
ethics is probably due to a combination of the importance of law in Western thought and
a particular way of reading the Bible that became standard. Virtue ethics can have a
theological foundation also, whether or not it has the form I have proposed here. There
are also forms of virtue theory that lack an explicit theological foundation but are
compatible with a religious explanation for the existence of value. Whether ethical theory
on its metaphysical side needs religious theory is an issue that cannot be disentangled
from the general question of what is required for an acceptable metaphysics. When
naturalistic ethical theories are preferred to religious ethical theories, it is not because
they are thought to be superior as ethical theories, but because it is thought that
naturalism is superior to religion. That, of course, is not a dispute that will be resolved
within ethics.
Religion and the Task of Developing a Common Morality
Moral pluralism is a challenge to every kind of moral theory, whether or not it is
religiously based. Apart from the issue of the justification of one moral system over
others, there is the problem of developing a common morality. As I pointed out in the