"You can be mistaken about what the good and right is. Certainly this is not an argument that our moral perceptions are infallible. We make mistakes all the time, but the very fact of moral error points to the objectivity of these values. If they are not objective, you can’t err or fail to do the right or good thing because it is all subjective anyway. So the very fact of moral error and moral disagreement and moral failure actually presuppose the objectivity of moral values and duties"