So it is the careful distinction of moral ontology and moral epistemology which answers some of the more common objections to objective morality.  To wit:

There is no such thing as objective morality.  On the other hand, we should really put an end to [morally objectionable behavior of the day].

We see here that one cannot deny the existence of a moral standard, then meaningfully apply that non-existent standard to whatever he feels strongly about.  It is utter nonsense.  Moral ontology must be real for moral epistemology to mean anything.

Evolution explains all of our moral proclivities.  We are simply driven to survival, and whatever promotes human well-being is good.

But why is human survival good?  What if humans never existed, then what would be good?  This is a claim to definitive moral epistemology without having the corresponding moral ontology to support it.  It is a house without a foundation.

Our present case follows the movement from moral epistemology (eg. specific moral judgements we make) to moral ontology (i.e. the existence of some Good by which we make our judgements).  If we agree that there are true moral judgements we can make, then what is the standard by which we make them?

Now this standard must be an objective reality, or else it becomes a relative one.  If relative, then we are back to square one – our moral judgements aren’t what we think they are.  What is good might depend on your geography, your place in history, whether you are standing on your head or on your two feet.  It is famously asked – Is rape wrong on Andromeda?

Well, is it?

So the Good is an objective reality.  It must also be true outside, or beyond, time and space.  That is, the Good is not a physical object, is not subject to any physical laws.

If it were, then our moral judgements are subject to change; the most heinous crime today could be morally acceptable tomorrow.  If the Good could decay, like a physical object, the greatest act of goodness today may be evil tomorrow.  This is not how we think of our moral judgements.

Thus, the Good is objective and immaterial.  What sorts of “things” could qualify as the Good?

We have Plato’s “form of the Good,” which is the greatest form in the world of forms.  Our world of physical objects, Plato says, is patterned off the world of forms.  And like our meditation so far, Plato envisions the form of the Good as something analogous to light; so that, in view of the Good, we see everything else clearly.

If that sounds abstract, that’s because it is.  Finding candidates for “the Good” requires a turn to the abstract.

What else would qualify?

Aristotle carried this penultimate reality further – if not exactly in a moral capacity – and gave us the Unmoved Mover, a being necessarily outside of the physical world who was unchanging and eternal.  Christianity, born monotheistic, married these Greek concepts and attributed them to God.

So, not simply a standard, an abstraction of the Good, but the Lord Almighty, Creator of heaven and earth.  God qualifies as the Good.

There may yet be some other candidate for the good, but anyone nominating must keep her eyes on the qualifications.