PlatoVirtually all moral theories end up with a subjective version of morality (including evolutionary explanations of morality), in which moral values have their genesis in the human will in one way or another. In our moral experience, however, we have a basic moral intuition that moral values are objective.

To say a moral value is objective is to say its truth value does not depend on any human knower. So, for example, to say that killing Jews simply because of their ethnicity is immoral in an objective sense is to say that killing Jews is wrong whether anyone believes it to be wrong or not. If Hitler had won the war and eliminated everyone that thought the Holocaust was immoral, such that everyone believed it was moral, it would still, in fact, be immoral.

For a moral value to be objective it must be grounded in a source that transcends human beings (if humans invented the moral values, or if the moral values only came into being when humans came into being, then they would be relative).  The only two viable sources for objective human values is a personal God whose very nature is good, or abstract objects in some Platonic realm.

Since I have defended the existence of God as the best explanation for the existence of objective moral values elsewhere (here, here, and here), I will limit my thoughts to why moral Platonism fails as an adequate moral theory.  Here are eight reasons we have to reject Platonism as the grounding for objective moral values:

  1. Why think abstract objects exist? – It’s taken for granted that there is a realm of abstract objects which includes things such as love and justice, but why should we think such a realm exists? After all, if there are no good reasons to think it does exist, then the atheist cannot help himself to any of the supposed existents from that realm. What is the argument?
  2. Moral values are not abstractions – How could moral values exist as abstractions apart from minds? Think of justice.  It makes sense to understand someone as being just, but it doesn’t make much sense to think that justice can exist as an entity in itself.  The concept of justice itself is not just, in the same way that quickness is not quick, nor laziness lazy.  To be meaningful, these abstractions must be mind-dependent.
  3. Why think some abstract objects have the unique property of possessing moral value? – There are an infinite number of abstract objects, so why is it that we have a moral duty to obey some abstract objects but not others? Platonists cannot explain why some abstract objects have the unique and queer property of possessing moral value, but others, such as the number two, do not.
  4. Unable to discriminate good from evil abstractions – Abstract objects inveighed with moral properties are not limited to kindness, fairness, love, and the like, but also include hatred, selfishness, and greed as well. Why, given the impersonal nature of abstract objects, am I obligated to be kind, fair, and loving, but prohibited from hating, being selfish, and being greedy?  What is it about the former group of abstract objects that makes them good, whereas the latter group evil?
  5. Cannot ground moral duties – Even if it could be shown how certain abstract objects are invested with the property of having moral value, the Platonist still cannot explain why we are morally obliged to obey them. Why think they apply to us? Why not ignore them if we choose?  Are the abstract objects going to enforce themselves?  Clearly not.
  6. Abstract objects, particularly moral objects, require thinkers – Abstract objects are objects of thought. It makes no sense to think of objects of thought existing for eternity without thinkers to know them.  Indeed, what applicability would abstract objects like love, justice, fairness, tolerance, and the like have apart from personal minds?  These sorts of objects require the existence of minds to even be meaningful.  Human thinkers have not existed for eternity, so the existence of these abstract moral objects would require an eternal mind, which we would identify as God.  As Alvin Plantinga writes:

    How could there be truths totally independent of minds or persons?  Truths are the sort of things persons know; and the idea that there are or could be truths quite beyond the best methods of apprehension seems peculiar and outré and somehow outrageous.  What would account for such truths?  How would they get there?  Where would they come from?  How could the things that are in fact true or false propositions, let’s say-exist in serene and majestic independence of persons and their means of apprehension?  How could there be propositions no one has ever so much as grasped or thought of?  It can seem just crazy to suppose that propositions could exist independent of minds or persons or judging begins.  That there should just be these truths, independent of persons and their noetic activities can, in certain moods and from certain perspectives, seem wildly counterintuitive.   How could there be truths, or for that matter, falsehoods, if there weren’t any person to think or believe or judge them?

    If God must exist to ground abstract moral objects, then it makes better sense to ground moral values in God rather than abstract objects.

  7. How are we aware of abstract moral objects? – Abstract objects are causally impotent, meaning they have no causal relations to their instantiations in the physical realm. The number two, for example, doesn’t cause anything.  Given their causal impotence, how could we ever come to know that such a realm exists?  Remember, our basic moral knowledge is known to us via moral intuitions.  Wouldn’t it be a bit odd, if God does not exist, that we evolved in such a way that knowledge of the Platonic realm is built into us, such that we cannot not know abstract moral objects?
  8. Unable to distinguish the good from the right – Moral theory makes a distinction between what is morally good and what is morally right. Goodness refers to the ethical quality of the thing in itself, whereas rightness refers to our obligation to perform that which is good.  Not everything that is good is right.  For example, it’s surely a moral good to become a doctor to help heal people of their ailments, but one does not have a moral obligation to do this good.  If moral truths are impersonal, abstract objects, and if one thinks we are morally obligated to these moral values, what basis could there be for saying we are morally obligated to obey some abstract moral values, but not others?  If we have any moral obligations to keep them at all, it would be to keep all of them.  In the end, we are obligated to do every good that can be done, which is impossible.

I would recommend this short video in which William Lane Craig explains why the Platonic explanation is inferior to the theistic explanation, in which he explains a few of the reasons I included above.

Moral Platonism only explains one aspect of our moral experience: how the moral truths we apprehend are objective in nature.  Moral Platonism, however, is utterly incapable of explaining how moral values exist as abstractions, how we apprehend them, why some have the property of being good while others have the property of being evil, why we have a moral duty to obey them, and the like. The best explanation for the existence of objective moral values is the existence of a personal God whose very nature is the good.