"Naturalism, Theism, Obligation and Supervenience" — Alvin Plantinga
"I propose to support the claim that naturalism cannot accommodate morality—not by showing directly that it can’t, but by displaying the failure of the most natural way of arguing that it can."1...where the "most natural way" (punny!) falls into this pattern: There is a "naturalistically acceptable" property N which is equivalent to a given moral property M in the sense that if something has property N, it necessarily has property M (and vice versa). Therefore God isn't needed to account for moral properties.
Classic Utilitarianism provides a convenient example of a naturalistic property: "maximizes the world's hedonic index." If five actions are open to me, one of them might have the property of doing the most to increase pleasure among all sentient beings in the world. According to classic Utilitarianism, any action with this property also has the property of being obligatory (and vice-versa).
Why couldn't a Utilitarian say these two properties are equivalent, note that God wasn't invoked, and shrug off claims that God is required for moral obligation? This is where Plantinga's dilemma about equivalent properties comes in.
"Identical" Option — Equivalent Properties Are Identical
As Plantinga puts it, "if a property A is equivalent to a property B, then A is identical with B." That probably sounds redundant, but remember he is defining equivalent properties as those which necessarily appear as a pair. If they always and only appear together, it's easy to see the attractiveness of declaring them one property rather than two. Occam's Razor, right?
"Non-identical" Option — Equivalent Properties Aren't Necessarily Identical
Plantinga questions whether the property of being the [principal] square root of 9 is the "very same property" as being the fifth root of 243, among other counter-intuitive examples. It's not important to resolve the debate about which view of properties is correct because both options, Plantinga argues, are bad news for naturalistically acceptable morality.
The Possibility of Divine Command Ethics
Readers are asked to consider the possibility that "[w]hat makes an action A obligatory is that it is an essential property of God to command all persons to perform A." In this scenario, it may still be the case that a naturalistic property lines up with obligatory acts. God might, for example, command all persons to perform actions with the property of doing the most to increase pleasure among all sentient beings in the world. Classical Utilitarians would have correctly identified a property which:
- always and only belongs to obligatory acts
- does not mention God
- (yet) is not the property that makes those acts obligatory
"Given [the non-identical option], therefore, one can’t show that rightness or moral obligation is naturalistic by showing that it is equivalent to a naturalistic property."2Meanwhile, it might seem at first like the identical option can show that moral obligation itself is naturalistic once someone can show that it always and only appears in conjunction with a naturalistic property (since this would show they are the same property). But if obligation also always and only appears in conjunction with a God-based property, then the naturalistic property, the property of obligation, and the God-based property would all be one and the same property according to the identical option! Therefore, the apparently naturalistic property was a God-based property all along.
"[I]f [the identical option] is true, then not even showing that obligation is identical with some naturalistic property will suffice to show that obligation is naturalistically acceptable; for obligation might well be identical with a naturalistic property, but also identical with a property obviously entailing that there is such a person as God."The Big Conclusion
Under either complementary view of equivalent properties, demonstrating the equivalence of obligation with a naturalistic property fails to prove that obligation itself is a naturalistic property.
Wait A Minute
Why should any of this bother a naturalist? Heck, Plantinga outright affirms "there are naturalistic properties that are logically equivalent to obligation." A few provocative declarations aside, Plantinga appears to spend the whole paper arguing that this equivalence relationship is compatible with a certain kind of Theism, not that it is incompatible with naturalism.
All I've learned is that naturalism can't accommodate morality in hypothetical cases when naturalism is false anyway. This paper is probably of more interest to a Theist who is troubled by the strong ties moral properties have to naturalistic properties; it's a way of holding onto the possibility that moral properties are God-based even if they always and only appear in conjunction with (apparently) naturalistic properties.
1. Faith and Philosophy. Volume 27, Number 3 - 2010.
2. I'm substituting "non-identical option" for Plantinga's term 'abundantism' and "identical option" for his term 'sparsism.' I found his terms to be a confusing adaptation of David Lewis' usage and not needed for my own explanation.