I would like to thank Joslyn Barnhart for her kind and thoughtful review of my book. I learned quite a bit from her book, so I was pleased to read that she also “learned a tremendous amount” from mine. Regarding the issue of whether my historical case studies would convince a skeptic, I have two responses. First, in the empirical case studies, I reviewed philosophical texts that may seem to conflict with my argument along with texts that seem to confirm it. Given the difficulty of convincing a skeptical reader that I was not just cherry-picking quotes, this seemed like a reasonable strategy, though I now realize that perhaps I could have been a bit more thorough. Second, I see the overall argument of my book as a kind of “inference to the best explanation.” In other words, if there is any evidence at all that human beings across cultures share similar values, this requires an explanation—one that even the most skeptical reader would have to provide. One goal of the book was to develop a theory that plausibly explains these similarities. Of course, as with any social phenomenon, it is always possible that the similarities in values that I detected could have arisen by random chance. But given what we know about the nature of individual moral psychology (which I review in the first part of the book), my claim is that the likelihood that these similarities occurred by random chance is relatively low.

Barnhart also asks “how we are to understand our observed world differently after reading this book.” Specifically, because individual moral psychology is relatively malleable, “how far does this argument alone get us if we do not then understand what causes the expression of one moral intuition in a time or place?” The simple answer is “not that far, but farther than we would without it.” The more complicated answer is that no one theory alone can get us where we want to go. Because the world is complex, political science should not be monocausal. To explain more precisely how international norms emerge and develop over time, my theory should be combined with other theories that emphasize alternative causal factors and mechanisms.

That said, one of my goals in writing the book was to build a case for the idea that some of our moral intuitions are universal and innate. To the extent that the final product came anywhere close to achieving that goal, then I think that the book narrowed down the residual space for explaining what “causes the expression of one moral intuition in a time or place.” In terms of “how we [as political scientists] are to understand our observed world differently after reading this book,” I would simply say that I hope we build more space in our worldviews and theoretical paradigms for the more universal aspects of human nature, especially the moral aspects of human nature.