Unless one is a cartesian skeptic, one accepts some things that haven’t been proven absolutely. Presumably, the basis of our core beliefs is perception of things. One accepts that the physical world is real, after all, because we perceive it. While it is true that one may be wrong to do so, it seems far more reasonable than to believe that reality is all simply a delusion.
Many who are deeply committed to the reality of the physical world, however, are hostile to this same reasoning process when applied to other areas.
In this case, I’m speaking of moral truth.
Many insist upon “evidence” for objective morality, by which they seem to mean something that can be shared via the senses. Apparently, we need no evidence that the senses are reporting (however imperfectly) a real world, but we need evidence that the moral sense is (again, imperfectly) a touchstone of the real.
This seems completely inconsistent, and the only response I’ve ever been given is descriptions of moral beliefs in terms of the physical (i.e. sociobiological evolution). Surely, one can do this. But one can equally explain the physical in terms of the mental (or even the moral). This disproves the reality of neither. Nor does it establish that one simply reduces to the other.
All this seems to show is that the truth is difficult for humans to understand. But this seems a reason to be more, not less, open to seriously considering multiple facets of reality. Walling one’s mind off from anything which doesn’t fit into a particular category which is easy for us to investigate is not seeking truth.
I suspect that, were it not for the current zeitgeist, it would be next to impossible to believe that having a physical explanation of a thing precludes the validity of any other kind of explanation. That is rather tidy, but isn’t any more defensible than a similar argument against the physical.
That being the case, I’m inclined to think that (while I may misperceive it, as I do the physical) moral truth is as real as the physical universe.