The joint 108th American Society of International Law (ASIL) Annual Meeting and 76th International Law Association (ILA) Biennial Conference was organized under the theme “The Effectiveness of International Law.” In conjunction with this theme, the ASIL Legal Theory Interest Group hosted a panel discussion exploring the theoretical dimensions of the concept of “effectiveness” as understood in international law. Panelists discussed three related questions:

1. (1) Is the effectiveness of international law an empirical question measured through evaluating compliance with international legal norms?

2. (2) What conceptions of effectiveness might exist beyond compliance? Could such conceptions be captured in theoretical or moral terms?

3. (3) Why is international law concerned with effectiveness at all?

Customarily one begins a discussion about the effectiveness of international law by quoting Louis Henkin’s famous remark that “almost all nations obey almost all principles of international law and almost all of their obligations almost all of the time.” For some, this empirical claim supports the notion that international law is a vital tool for furthering international cooperation across a broad range of issue areas. For others, the implicit suggestion that international law’s mere existence might be driving states’ behavior is a calamity of causal inference. Even if Henkin’s claim is empirically correct, effectiveness does not follow from compliance. For a third group, Henkin’s claim may not even be empirically correct. In at least some areas of international law, noncompliance may be relatively high. Deploying the same suspect causal reasoning that the second group worries about, international law skeptics have sometimes suggested that we might infer ineffectiveness on the basis of such noncompliance.

What would it mean for international law to be effective? There are different senses of the word. In a dis-cussion of the idea of effectiveness, then, the first step is to distinguish a variety of different ideas. The aim is not to decide which sense of the word is the right one, conceptually or linguistically. The aim should be to discuss which of these ideas of effectiveness is important, worth thinking about.

When we think of “effectivity,” we usually come to think of a pragmatic and factual construction. The idea of effectivity, however, is anything but concrete and raises a variety of questions of legal theory, legal philosophy, epistemology, and theory of knowledge. It should also be highlighted that from a linguistic standpoint the word effectivity does not exist in British English. The attachment of the International Court of Justice to her Majesty’s English explains that the World Court uses the French word (effectivité) when it seeks to refer to effectivity. These linguistic debates, however, matter less than the semantics and especially less than the consensus that effectivity ought to be opposed to “effectiveness.”