Meta-ethical non-naturalism refers to meta-ethical theories which hold that moral terms such as “good” and “bad” and the entire domain of morality and ethics cannot be reduced to any natural properties of the universe, but that moral properties nevertheless exist objectively and are knowable by non-empirical means such as intuition or pure reason.
The first problem with meta-ethical non-naturalism is that it relies on means of “knowledge” that can’t be verified or demonstrated to be reliable in any meaningful way. Equally important, one person’s intuitions or a priori reasoning can lead to very different moral notions than the intuitions or a priori reasoning of another, and there is no way to objectively or impartially adjudicate whose views correspond or are more likely to correspond to purported moral truth. The “head count” approach in which the views held by the majority are treated as more likely to be true or valid does not help matters, as it is entirely possible for the majority of people to be wrong. Indeed, the majority of people have been wrong many times in human history. This is true if even one person’s intuitions or a priori reasoning could conceivably lead to different moral beliefs than those of most or even all other people, as it would still be impossible, even in that situation, to adjudicate which view was correct—it would still only reveal what people believe, not whether those beliefs were correct. But in any case, it is not necessary to posit such a fantastic scenario, as it is self-evident that different peoples’ intuitions and a priori reasoning regularly lead them to very different opinions about morals on a regular basis.
The second problem with meta-ethical non-naturalism is that it lead to the positing of moral views that are not falsifiable in any way. They are not merely not falsifiable by experiment— they are not even falsifiable by another person’s intuitions or a priori reasoning, as these would not prove that moral beliefs derived from a previous person’s intuitions or a priori reasoning are false, but only the banal fact that the people in question disagree about moral truth. It would lead to an impasse and there would, again, be no objective or impartial way to adjudicate whether one was correct or both were incorrect. In practice, this means that moral beliefs derived from intuitions or a priori reasoning could only be accepted or rejected on the basis of some sort of faith in one particular set or type of intuitions and/or a priori reasoning.