Some of you are finding it hard to believe in Moore’s non-natural moral properties (and that is perfectly understandable, as we’ve seen), but before you all commit yourselves to subjectivism or relativism, here are a couple of articles that might give you another perspective.
The first takes a logical approach – it should be an interesting read for you, even just to see how logic ties in with ethics. I’m not sure I’m entirely convinced by it (I’d be happy to discuss it with you) – but see what you think.
The second takes an evolutionary approach. Evolutionary biology and psychology are generally appealed to in order to debunk realism (the idea being that since our morality has evolved, and evolution takes somewhat arbitrary trajectories, our morality is therefore subjective, and there are no objective truths about moral facts. We just happen to have become the sort of creature with our particular moral values).
In this article, the authors seem to want to relate natural goodness, through the concept of “fitness”, to moral goodness. Unfortunately only the first two pages are available here, but I will be trying to obtain a copy for myself.
Finally, Steven Pinker makes a strong case for moral rationalism in this Ted Talk.