Beyond Euthyphro: The Quadrilemma Against Theistic Grounding of Moral Values

Here's a sketch of an argument against the necessity of God for (objective) moral values.

Consider the following position:

DNT-A: Moral values are grounded in God's nature.

The motivation for this position collapses once we map the logical space of possible grounding relations. Once the options are laid out, it becomes clear: God or God's nature is not required to ground moral values.

The Quadrilemma

If objective moral values exist, their ultimate foundation must be either ungrounded, abstractly grounded, mentally grounded, or physically grounded. 

• Ungrounded. Some moral values are fundamental. For example, "kindness is good" is simply a brute, foundational truth.
• Abstract grounding. Some moral values are grounded in other abstract properties or value-relations. For example, the badness of cruelty may be grounded in the disvalue of causing suffering.
• Mental grounding. Some moral values are grounded in a mind or intellect, such as a divine being's valuing activity.
• Physical grounding. Some moral values are grounded in facts about the natural world, such as human flourishing, evolutionary facts about cooperation, or the requirements of well-being.

These four horns are mutually exclusive and jointly exhaustive. There are no further intelligible options for grounding moral values.

Objection: God's Nature is Sui Generis

One might object that the grounding of morality in God is sui generis—a unique, fifth kind of relation not captured by these categories. But is it? To count as a legitimate fifth option, it is not enough simply to assert that it is sui generis. The proponent must explain what this fifth option is and how it differs from physical, mental, and abstract grounding. Unless and until such an account is provided, there is no reason to accept it as a genuine alternative. Therefore, the quadrilemma covers all the intelligible philosophical options.

Why God's Nature Is Not Necessary

Now consider the implications of each horn.

• Ungrounded: If some values are (ontologically) fundamental, then they do not depend on God by definition. While a theist might respond by proposing God (or His nature) is the ultimate ground of axiology, this view is counterintuitive, less parsimonious, and possibly incoherent.

• Abstract grounding: If values are grounded in abstract properties like <kindness> or <justice>, it's far more parsimonious to say that they are grounded in abstract properties, full stop, than it is to say “and they are essential properties of God.”  Why the middleman? There is no compelling reason to require that moral values be instantiated in God rather than being recognized as foundational abstract properties. 

• Physical grounding: If values are grounded in natural or physical facts, then again God is unnecessary.

• Mental grounding: If values are grounded in a mind, then God is a candidate. But this option is inconsistent with DNT-A, which says that moral values are grounded in God's nature, not God's mind. Proponents of DNT-A might try to reconcile this with their 'nature' claim by asserting that God's mind and nature are identical. Not only does this move depend on the highly contested and arguably incoherent doctrine of divine simplicity, it still fails to show that God is necessary. The grounding could potentially be in a different sort of mind, making the theistic option one possibility among others, not a requirement.

Beyond Euthyphro

The famous Euthyphro dilemma pressed divine command theory with two horns: are things good because God commands them, or does God command them because they are good? Some thinkers have argued that Modified Divine Command Theory, with its appeal to God’s essentially good nature, shows that the Euthyphro dilemma is a false dilemma.

But the quadrilemma is more difficult to escape. It does not presuppose voluntarism or command theory. It partitions the entire logical space of value grounding. And once the options are on the table, the apologetic claim that (objective) moral values require God can no longer be sustained.

Conclusion

The Quadrilemma Against Theistic Grounding shows that God is never necessary to ground objective moral values. At most, God offers one possible grounding among others. The real question is not whether objective moral values can exist without God. They can. The real question is which grounding theory has the best explanatory virtues, such as parsimony and coherence. On these grounds, non-theistic options appear to have a distinct advantage.