Consent and Customary International Law

Written by

I am pleased to see Professor Guzman and Jerome Hsiang being among those authors who admit that one cannot construct a plausible and coherent CIL theory without a thorough conceptual clarification. In their short article in EJIL Vol. 25:2 (2014), they are focusing on consent and CIL, particularly on the tension between the principle of consent prevailing in international law and non-consensual law-making in the field of CIL. They do not perform an analysis on the concept “consent”, but try to answer the question of why rationally self-interested states should accept the existence of non-consensual customary rules in international relations. I am willing to accept some of their claims or conclusions, as follows. (i) There exist some weak, limited forms of non-consensual rule-making in contemporary international law. (ii) Customary rules are the output of such rule-making. (iii) A non-consensual customary rule, by its content and nature, usually provides great benefits to most of the states or the whole international order and relatively small costs to one or some states.

Of course, all this is the rejection of the so-called consent theories of CIL. It is no surprise. In his excellent, seminal article of 2005 (Saving Customary International Law), Guzman has outlined the basis of a modern, non-objectivist, belief-based CIL theory within the framework of his rational choice doctrine. A belief-based CIL theory is not compatible with consent theories. I also have doubts about that a consent theory could adequately explain how CIL really works. However, three caveats are in order here.

First, consent theories of CIL put up a stout resistance. They are supported by the requirement of “acceptance” in the text of Article 38(1)(b) of the Statute of the International Court of Justice, although they encounter difficulties with adjusting acceptance to opinio juris. For example, Olufemi Elias and Chin Lim, who worked out a modern, refined and flexible version of CIL consent theories (The Paradox of Consensualism in International Law), simply conflate the two concepts, which is problematic from the theoretical angle. However, their theory found some support in the pragmatic method used by the ICJ of reconciling acceptance and opinio juris (the test of individual consent, thoroughly analyzed by Elias and Lim). The essence of this approach is that the Court first tries to apply the twin general requirements of general practice and opinio juris to the case in order to determine whether the international community has developed a particular customary rule. Then it examines whether the State party to the proceedings, for which this rule would create a specific international legal obligation, has individually recognized (accepted) the existence of this customary rule, e.g. Libya/Malta Continental Shelf(para. 34.) or Gulf of Maine (para. 94.)

Second, it is easy to fall into the trap of such doctrinal clichés like that CIL is the source of international law. It is misleading. I maintain [EJIL 25:2 (2014), pp. 529-552] that if CIL is part of international law then it cannot be its source. It cannot play both roles. A source of a phenomenon cannot simultaneously be part of this phenomenon. One has to make a choice, which will then determine the nature of the theory relating to CIL.

Third, I am somewhat puzzled by the way that the conceptual foundations of CIL are treated. In a non-objectivist CIL theory, (which excludes State practice from the defining elements of CIL), one has to choose a default state of mind in which customary rules appear. In his 2005 article Guzman correctly identified this state of mind as belief, and later Brian Lepard built up a nice belief-based CIL theory (Customary International Law), identifying CIL as beliefs. (For a recent and improved non-objectivist CIL theory, see “Law in Mind: Towards an Explanatory Framework for Customary International Law” in the forthcoming 2014 issue of the Hungarian Yearbook of International Law and European Law). But now Guzman and Hsiang departed from this CIL-as-beliefs scheme suggesting that customary norms themselves are not beliefs, but only created by beliefs. If customary norms are not beliefs, what they are? In their article they repeatedly make reference to the perception or “sense” of legal obligation (as many authors do in the literature, relating to opinio juris), arguably advancing another form of non-objectivist theories. It is suggested that (i) States’ beliefs create customary norms; (ii) customary norms appear in opinio juris; (iii) opinio juris is equal to the sense of legal obligation; therefore, customary rules exist in the form of “sense” of legal obligations. If this is the case, then we have a different story. The sense or perception of legal obligations is inconsistent with belief. A belief in something (which suggests a strong cognitive commitment) should not be mistaken for the sense or perception of something, which is phenomenal in nature. If someone believes in something, s/he does not (only) have a sense of something (they are like night and day in psychology or philosophy of mind). One must choose between a belief-based CIL theory grounded on a CIL-as-beliefs scheme [Guzman (2005) or Lepard] and the non-objectivist claim that CIL is only sense or perception of legal obligations [Guzman and Hsiang (2014)].

I hope it does not seem hair-splitting. We can’t spare the trouble of doing the groundwork for a plausible CIL theory. This is the level where conceptual clarification begins.

Print Friendly, PDF & Email


No tags available

Leave a Comment

Comments for this post are closed


Mihai Martoiu Ticu says

August 4, 2014

Describing CIL in cognitive terms, like 'sense' en 'believe' seem to me problematic. States do not believe anything, people do. What if we change the formulation and say that CIL is what relevant representatives of the state believe. We still do not solve the problem. Who is the relevant believer in the US government? Obama? His legal advisers? The whole government? What if Bush has declared that he believes something and Obama does not believe it, but never declares officially that he does not believe it. Bush's belief helps creating a customary rule that will be binding on the US despite the fact that Obama believes something else. Even if Obama claims to believe something it might be a lie, he might believe something else.

A better solution would be to redefine the Opinio Juris in terms of declarations: there is evidence that the representatives of a state treated a rule as a customary legal rule. For instance the state's A representative has sent the ICJ a letter during a case stating that the customary rule is X according to state A.

Thus we should define opinion juris in terms of evidence that the state representatives treat a rule as a rule.

Jordan says

August 5, 2014

First, there are many actors other than the "state" with formal participatory roles (such as nations, peoples, tribes, belligerents). Second, there can be many evidences of formal actor patterns of legal expectation (or opinio juris). From a Realist perspective, see

Jordan says

August 5, 2014

Third, as the free download (as annonymous) click-on notes, "consent" can be relative and even an illusion.
Regardng the fact that international law has never been merely state-to-state, see