Readers of my blog know that I have been debating whether the is/ought dichotomy is compatible with theistic metaethical realism . I’ve taken the stance the odds the is/ought dichotomy is true are at least as probable as the odds the is/ought dichotomy is false. Since the is/ought dichotomy is incompatible with theistic metaethical realism, and there are more ways to be a moral realist who denies the is/ought dichotomy than theistic metaethical realism, the odds theistic metaethical realism is true are less than 50%; thus, theistic metaethical realism is not obviously true. The preceding argument can be extended further: since theistic metaethical realism is less than 50% likely to be true, we should not be theistic metaethical realists. In place of theistic metaethical realism, I have suggested metaethical non-natural realism: the view that there are non-reducible objective moral truths that constitute their own fully autonomous domain of facts. Richard Bushey has argued the is/ought dichotomy and theistic metaethical realism are compatible , but, thus far, I have found his substantive challenges unconvincing. Here, I respond to another possible argument that the theist may provide against meta-ethical non-natural realism.
The theist may argue that, if the meta-ethical non-natural realist is correct, then it is difficult to explain how we know what moral truths there are. Moral truths would not have any spatial or temporal location, so we cannot observe them in the world; they would have no causal efficacy, so they could not cause various events that we observe; and our brain’s access to non-physical moral truths is mysterious. But, the theist may argue, theistic metaethics does not suffer from these problems. For theistic metaethics, God produces all moral truths, which He communicates to us through divine revelation . The argument can be put formally as follows:
- Our moral knowledge is unexpected on meta-ethical non-natural realism.
- Our moral knowledge is expected on theistic metaethics.
- Therefore, theistic metaethics is probably true.
We can call this the epistemic worry. In what follows, I will provide a response to theistic proponents of the epistemic worry. First, I will comment on a weaker version of the epistemic worry and show that the weaker version is incompatible with the theist’s moral argument for the existence of God. Afterwards, I demonstrate that a stronger version of the epistemic worry is not successful.
Let’s turn to the weaker version of the epistemic worry. Many proponents of theistic metaethics advocate the moral argument for God’s existence:
- If God does not exist then objective moral truths do not exist.
- Objective moral truths do exist.
- Therefore, God exists.
The proponent of meta-ethical non-natural realism questions premise 4 because, on their view, objective moral truths exist with or without God. They do not deny premise 5, for they agree with the theist that objective moral truths exist. However, the proponent of the moral argument does not restrict themselves to arguing against moral realists, so 5 is not always uncontroversial between the theist and the atheist. For the theist to show the moral argument is sound, they need arguments for both 4 and 5. What sort of argument might the theist provide for 5? If the theist’s argument for 5 appeals to God, they have assumed what they seek to establish. But if they argue for 5 using arguments that are independent of God, then they have conceded that one can establish moral truths exist without appealing to God. So the moral argument advocate should not say that the existence of moral truth can never be established without appealing to theism. Instead, the moral argument proponent should say that there are arguments for the existence of moral truth that are God-independent, but that moral truth, once established, is evidence for theism.
There are moral argument proponents who, when arguing for 5, appeal to moral convictions the atheist already possesses instead of arguing that the existence of moral truths can be established through some God-independent means. However, whether or not the atheist believes moral truths exist has little to do with whether there are moral truths; so the moral argument proponent cannot establish 5 by appealing to the atheist’s convictions. Moreover, theists and atheists often disagree on what is moral, so the theist cannot establish the moral truths they endorse by appealing to the atheists’s endorsements. Thus, to establish 5, the theist must concede the existence of moral truths can be established without appealing to God. Nonetheless, the claim that exist moral truths exist is not a claim about which moral truths there are, so the theist may retain the view that specific moral truths can only be established with reference to God.
I advertised that I would consider a weaker version of the epistemic worry. The weaker version states the existence of moral truths could never be established without appealing explicitly to God, so no secular moral theory can succeed. I call this a weaker version of the epistemic worry because it entails 1 and 2, but anyone advocating the moral argument (at least as described in 4-6) must deny that theism is required to establish the existence of moral truths. Most theists advancing the epistemic worry advovate the moral argument, so they must, on pain of contradiction, endorse that theist and atheist alike recognize moral facts.
However, the weaker version highlights a general difficulty for the epistemic worry. If God exists, God would have both the ability and the desire to ensure that Her revelations were understood as originating from Her. Nonetheless, the moral argument proponent must grant that the existence of objective moral truth can be established without appealing to God. Thus, we are led into a contradiction: how could the existence of moral truths be established without reference to God if we could only know about moral truths through explicitly divine revelations? Theists may reply God possesses reasons, incomprehensible to us, for revealing moral truths in a sufficiently ambiguous way that they are not obviously divine revelations. However, if we allow the possibility God possesses reasons to provide revelations whose origins are mysterious, the probability that God reveals moral truths is rendered inscrutable. We wouldn’t know whether the moral truths, as we perceive them, were either likely or unlikely to be the ones God reveals. The theist’s mysterianism is a point in favor of alternative views because mystery counts against explanations. Moreover, theistic metaethics proponents typically argue God’s authority has some special role to play not available in secular ethical accounts; for example, perhaps God’s supreme authority has the unique ability to create duties for us. But if God’s revelations are not obviously divine, how could they obligate us to various duties?
Onto the stronger version of the epistemic worry. The stronger version of the epistemic worry concedes there are convincing arguments for the existence of moral truths that do not appeal to God, but argues (as in 1-3) theistic metaethics is a better explanation of objective moral truths than meta-ethical non-natural realism.
There are several difficulties for the stronger version of the epistemic worry. I have already pointed out the first difficulty. If moral truths are only available through divine revelation, how could the theist justify 5 without begging the question? Any non-question begging argument for 5 is evidence against the view that moral knowledge requires divine revelation.
Putting this first difficulty aside, there are further reasons theistic metaethics proponents, who endorse the moral argument, should not endorse the epistemic worry. The non-natural moral realist might say that our moral knowledge is analogous to our mathematical knowledge. Consider how we know that ‘1+1=2′ is true. We reflect on the meaning of 1, +, =, and 2; anyone who understands the concepts those symbols represent cannot help but know that ‘1+1=2′. ‘1+1=2′ is self-evidently true for anyone who knows the meaning of ‘1+1=2′. I do not claim that ‘1+1=2′ is self-evidently true for all humans; perhaps some do not have a concept of one, addition, numerical equality, or two. But anyone who possesses the requisite concepts cannot help but see that ‘1+1=2′ is true.
Metaethical non-natural realists argue that many of our moral obligations are similarly self-evident. For example, the reason that we should follow through on promises, unless there are stronger overriding reasons, is because of the essential characteristics of promises . Of course, we should not follow through on all promises, since following through on some promises would be immoral. But the immorality involved in following through on any given promise would be a stronger, overriding reason not to follow through.
In defense of 5, moral argument proponents, such as Bushey and Craig, argue that we can know one should follow legitimate authorities merely from the nature of authority. As an example, they consider a situation where a police officer issues a command to a citizen. Craig writes:
Someone might demand, “Why are we obligated to do something just because it is commanded by God?” The answer to that question comes, I think, by reflecting on the nature of moral duty. Duty arises in response to an imperative from a competent authority. For example, if some random person were to tell me to pull my car over, I would have absolutely no legal obligation to do so. But if a policeman were to issue such a command, I’d have a legal obligation to obey. The difference in the two cases lies in the persons who issued the commands: one is qualified to do so, while the other is not. 
Richard considers an additional example involving a parent who holds authority over a rebellious teenager:
Suppose a rebellious teenager was told by their parents, “I know what is best for you. Listen to me.” After carefully contemplating who their parents are and what they have gone through in their lives, they decide that they are competent authorities and it is their duty to listen to them, even if they do not understand the moral commands that are being issued to them. 
Bushey insists that the teenager is making a rational, and not a moral, evaluation, but admits that there are “moral consequences”. Implicitly, Bushey has admitted that rational evaluations of the concept of authority have moral implications. Craig and Bushey are committed to a moral principle like one ought to obey worthy authorities and that this moral principle can be discovered by reflecting on the nature of authority. Craig puts this principle at the center of his view, arguing theistic metaethics is superior to “platonism” (or non-natural moral realism) because only theism provides a “competent authority” who “is uniquely qualified to issue such commands as expressions of His [sic] nature” .
We might be skeptical parents or police officers always yield legitimate authority and add further criteria to the examples Craig, Richard, and others offer – for example, the police officer or the parent must be reliably just. In any case, many proponents of the moral argument argue there is something about worthy authorities such that if one understands what worthy authorities are, one cannot help but feel a duty to that authority. In other words, merely reflecting on the concept of worthy authority grants us the knowledge that worthy authorities should be obeyed. I agree: there is something about the nature of worthy authority which compels our assent to their commands. On arguments endorsed by the theist, at least some moral truths can be known by conceptual analysis and not from revelation. But according to the epistemic worry, moral truths could be known only through revelation. Thus, the moral argument proponent should deny the epistemic worry.
Suppose the theist retorts our obligation to obey worthy authorities cannot stem from conceptual analysis after all and must have been provided through revelation. This response fails for the following reason. Suppose that we know of no obligation to obey the commands of worthy authorities and we receive a command – call it C – we know to be from God that we ought to obey the commands of worthy authorities. We would have no reason to obey C because we knew of no obligation to obey worthy authorities. Thus, our obligation to obey whatever God reveals cannot be only provided in revelation. (Of course, I do not deny that God, if God exists, might provide revelations that help us to understand our obligation to obey worthy authorities.)
Craig’s example highlights another worry for the moral argument proponent. If the moral argument proponent endorses the view that any worthy authority, whether a police officer, parent, or God, can create obligation, then we can have obligations independently of God. In possible (or counterpossible) worlds where police officers and parents exist but God does not, we are obligated to follow (worthy) parents or police officers, so 4 is false, and we would know we should follow their commands by reflecting on the nature of authority. Perhaps the moral argument proponent will object that our obligation to acquiesce to parents or police officers is not a moral obligation, but this is difficult to understand. After all, I am not considering our obligation to follow the commands of some arbitrary authority; I am considering our obligation to follow the commands of worthy authorities. As with promises, we may have stronger overriding reasons to disobey the commands of worthy authorities. And because our obligation to obey worthy authorities is categorical, only moral reasons could be overriding.
The theistic metaethics proponent’s insistence that moral obligations could only arise through divine commands is difficult to understand. There are normative obligations beyond moral obligation, and many of these obligations are non-controversially God-independent. For example, there appears to be a law of rationality according to which, whenever we see a belief b is justified, we ought to believe b . Similarly, Craig and Bushey argue whenever there is a worthy authority, we ought to obey that authority. God does not create either the principle of rationality or our obligation to worthy authorities, so both are God-independent normative truths. Given God-independent normative truths exist, I see no reason to posit God to explain morality. And given that we can recognize God-independent normative truths without God’s assistance, I see no reason to posit God to explain our moral knowledge.
I end with a suggestion for the moral argument advocate. The arguments advanced by the meta-ethical non-natural realist for their view – that moral facts are required for our deliberative discourse , that some moral facts are self-evident, etc – rely on our recognition of moral facts. The theist should use the metaethical non-natural realist’s arguments for the existence of moral facts to support 5 and should provide additional arguments for 4. Importantly, arguments for 4 should at least show there is no plausible secular moral theory, or that atheism entails moral nihilism. Doing so involves a substantial difficulty, because the moral argument proponent will have to demonstrate the implausibility of all possible secular moral theories, even the ones we have not yet thought of. Until the moral argument proponent does so, the secular moral realist is free to grant the existence of moral facts while maintaining moral facts are God-independent.
 Philosophers of mathematics will note that the epistemic worry parallels Benacerraf’s Objection. See section 3.4 in Horsten, Leon, “Philosophy of Mathematics”, The Stanford Encyclopedia of Philosophy (Spring 2015 Edition), Edward N. Zalta (ed.).
 Thanks to Eric Wielenberg for suggesting this example.
 Craig, 2010.
 See Shafer-Landau, R. 2004. Whatever Happened to Good and Evil?. Oxford: Oxford University Press, p 77; also Chad Vance’s lecture notes on Divine Command Theory, from which I took my example of a “law of rationality”.
 See chapter 3 in Enoch, D. 2011. Taking Morality Seriously: A Defense of Robust Realism. Oxford: Oxford University Press.