In the previous post, I said that generalizing from causation to explanation helps remove the difficulties posed by mathematical knowledge to causal theories of knowledge and content. What about knowledge of morality? The explanatory move does not seem to help. For not only is it mysterious how the fact that murder is wrong could cause us to believe that murder is wrong, but it is even mysterious how the fact that murder is wrong could help explain our belief. Again, just as in the morality case, bringing in God might help. If morality is grounded in the nature or will of God, then through God's power it might be efficacious on us—God might, in light of moral truths, create us with a propensity to believe these moral truths.
But again I want to suggest that there is a solution that is not explicitly theistic. Suppose an appropriate Natural Law theory is true. Then moral truths are grounded in the teleological features of our nature. Now our nature is not inert. It explains our development from embryo to adult. It is because rationality is a normative part of our nature that we as adults tend to exhibit rationality at least sometimes. This explanatory relation between our nature and features of us may be taken as final or formal causation (that is the classic Aristotelian way), or one might actually think it involves efficient causation, but in either case the way is at least open towards coming up with a story about moral knowledge or content that is compatible with the explanatory generalization of causal theories of knowledge or content. Whether in the end such a story would work is a further question.
The Aristotelian naturalist, thus, has the resources for resisting arguments for theism based on moral knowledge. Of course it may well be that an argument from the teleology of Aristotelian natures of the existence of God can be constructed.