Here now is a sketch of his argument for DCT in his own words (naturally, I'm leaving a lot out, but I think this does justice to the basic argument):
- If something seems like a command then it probably is
- Moral duties seem like commands
- So moral duties are probably commands (and as it turns out, Christians have a way of making sense of this)
When we experience the feeling of being morally obligated, we encounter that familiar experience of being commanded....When we perceive that something is right (i.e. morally required), it “seems” like we are perceiving that it is a thing we are commanded to do, and [putting adding premise 1 to the equation] that is because it really is a thing that we are commanded to do.Speaking for myself, that is not what I often experience when I perceive that something is right or wrong, obligatory, permissible, or impermissible.
I often experience a requirement that seems generated from what the rights of another individual seems to require. I lie to you when you have a right to the truth. I experience feeling like I have done something which your right requires of me which is inconsistent with your worth as another human person. I have not only wronged God, but I have wronged you.
Thinking of God, I experience approval, disapproval, or neither approval nor disapproval, more often than the experience of a command to do or refrain from doing something. If I were going to be a something akin to a Divine Command Theorist, I think I would be more inclined to be a divine approval (or perhaps intention) theorist, for approving of or intending some action seems more fundamental than the commanding of it or against it.
In fact, moral duties do not seem to me like commands at all. I'm a soldier in the Army. My sergeant commands me to lay down cover fire. My duty to lay down cover fire is not a command nor is it anything like a command (a command being a type of speech-act). The sergeant's command might (in part) generate a duty in me--a duty that I might not otherwise have, but the duty is not a command.
If this illustration is a good one, then it seems wrong to identify duties with commands. At best (and I'm skeptical that this holds for all duties), commands in some way explain or generate duties, but commands are not duties. The questions then are whether commands generate all duties and whether all duties are generated from commands of necessity. If so, then there is a type of Divine Command Theory which says that there is a strong relation between duties and commands but the relation is not identity.