Peter Spiro (and/or someone else operating the Opinio Juris twitter account) accuses me of “gloating” about the military intervention in Ukraine, being a “realist,” committing something called the “perfect compliance fallacy,” and believing that “international law is a chimera.” These accusations are false.

Julian Ku and Erik Voeten have already provided partial rebuttals. For the record, here are my views:

1. I am not a “realist” in the political science sense. I believe that countries cooperate when they can achieve mutual gains; that cooperation can benefit from sophisticated institutional arrangements; but that cooperation must be self-enforcing, meaning that it must be in the individual interest of the relevant countries not to defect from their arrangements (what economists sometimes call the “participation constraint”). Although few (albeit an increasing number) law professors take this approach to international law, many (although certainly not all or even most) political scientists do. Realism, as I understand that term, emphasizes security competition among countries; it has little value for understanding international law.

2. Spiro is right that you can’t infer anything from a single data point if that’s what he means by the “perfect compliance fallacy.” However, I never said that because Russia violated international law in Ukraine, international law is a “chimera.” Nor did I say anything that could be construed in such a way.

My writings about international law have been devoted to explaining it, not denying that it exists like the mythical beast invoked by Spiro. However, I am more skeptical than most international law scholars, who are frequently advocates, cheerleaders, or aspiring diplomats. The arguments I have made in The Limits of International Law, Economic Foundations of International Law, and elsewhere implied that international law is most effective at solving coordination games and managing bilateral cooperation, and not so good at solving collective action problems. So I have expressed skepticism about some types of international law–including collective security and human rights–but not others (trade law, for example). I have also argued that some areas of international law work under certain conditions but fail under other conditions–claims that are resisted by legal scholars but are familiar in political science (for example, James Morrow’s examination of the laws of war).

3. The evidence for the weakness of the use of force rules has been gathered and analyzed by many people, including Michael Glennon. The debate is too complicated to reproduce here. All I will say is that it is sufficient neither to point out that countries sometimes violate the law nor to point out that countries sometimes comply with the law. One needs to imagine the counterfactual world in which the UN system does not exist and ask how states would act differently. In such a world, would Russia have also invaded Armenia? Would the United States have invaded Canada? Countries have reasons other than law not to attack each other.