6. So it comes down to this. The moral relativist needs to ask himself whether he can establish some fundamental incoherence within the idea of objective morality which serves to unravel any system based on it. The moral objectivist needs to ask himself whether the denial of moral truth establishes some fundamental incoherence which makes it impossible to meaningfully speak about such things as morality, and then, if this is the case, whether it can be shown that the intelligibility of the moral relativist’s own speech and acts suffers (fatally) as a result. Can the relativist make sense of what he’s doing, given his relativism? Can he talk about things coherently?
7. I think it’s very difficult for the relativist to establish his side of the problem. I have never heard someone say that objective morality is fundamentally incoherent. However, the objectivist seems to have an easy time showing that relativism causes difficulties. This is what I was getting at in #4. A moral relativist (really, any sort of relativist) quickly loses the ability (are you reading this, E-Prime people?) to share a moral universe with anyone else. The motivations for acts the understanding of prohibitions and imperatives, etc., can no longer flow from things, but begins to be imposed on things by the mind. Instantly we end up with a thrasymachean world (which, given their rhetoric, is probably not what the relativist wants).
8. But more basically it’s impossible to explain to oneself why these things are desirable and other things are not. In other words, we’re reduced to a dichotomy: on one hand we have to resort to some nature to ground morality, in which case we find that we are actually objectivists; on the other hand, we can deny that any nature grounds morality, in which case we have to say that the moral agent is natureless, causa sui, and fundamentally unintelligible. We might say (like Sartre) that the moral agent is the ground of the intelligibility of his actions, but this really doesn’t explain anything. How do I positively bestow goodness on things? When do I choose to do this? Why would I choose either way at all? And in this case any rational or intelligible decision-making process dissolves completely, and another dichotomy presents itself: either human beings are machines suffering from an illusory consciousness and generates lies about its own behavior, or human beings are big fleshy random output generators and any attempt to make sense of what they do is futile. Whichever you choose you’re a nihilist, and no one wants to be a nihilist. (Provided their toes are all intact.) More relevantly, any talk about morality becomes meaningless.
9. So it seems like the moral objectivist wins.