The ICJ’s Judgment in Nicaragua v. Colombia: Back to the Basics

The ICJ’s Judgment in Nicaragua v. Colombia: Back to the Basics

[Keshav Somani is as an Associate with the Dispute Resolution team of S&R Associates, New Delhi]


The International Court of Justice on July 13, 2023, delivered its judgment in the case concerning Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia). The Court concluded by thirteen votes to four that under customary international law, a State’s entitlement to a continental shelf beyond 200 nautical miles may not extend within 200 nautical miles from the baselines of another State. An analysis of the Court’s decision on merits and unaddressed questions in the Court’s judgment can be found here. In this post, I will critique the Court’s methodology in paragraph 77 to find the existence of customary international law. I will explain why the majority’s approach is a significant departure from its earlier jurisprudence with regard to the law and its application to facts. 

The Court’s Methodology in Nicaragua v. Columbia

The Court bases its findings on State practice and opinio juris almost entirely on the submissions made to the Commission on the Limits of the Continental Shelf (CLCS) by the States parties to the UNCLOS. With regards to State practice, the Court relies on three key factors: a) vast majority of States that have not asserted their CLCS submissions an entitlement to a continental shelf that extends within 200 nautical miles from the baseline of another State; (b) only a small number of States that have claimed an extended continental shelf encroaching the maritime areas within 200 nautical miles of another State; and c) States objecting to the claims referred to in point (b). 

Further, the Court uses the same material, i.e., the CLCS submissions as an expression of opinio juris given “its extent over a long period of time”. On the question of opinio juris, the Court further relies on the Gulf of Maine judgment (para 111) to hold that the element of opinio juris can be demonstrated “by induction based on the analysis of a sufficiently extensive and convincing practice”. I will analyze the Court’s conclusions on State practice and opinio juris in the sections below.

State Practice

The International Law Commission (ILC), in its Draft Conclusions on Identification of Customary International Law, requires that State practice must be general, i.e., sufficiently widespread and representative (Conclusion 8). The ILC also states that while assessing State practice, contradictory and inconsistent practice must be taken into account (page 136). Moreover, while assessing the generality of practice, the practice of specially affected States must be considered as held by the Court in the North Sea Continental Shelf judgment (para 74).  

In the present judgment, the Court rightly gives weight to the practice of such coastal States whose continental shelf extends within 200 nautical miles of another State, for they are specially affected. However, it fails to consider the contradictory practice of several States that have claimed an entitlement to a continental shelf beyond 200 nautical miles that extends within 200 nautical miles from the coast of another State in their submissions to the CLCS. 

Judge Tomka analyses in great detail the above submissions to CLCS and even the pleadings of States before international courts and tribunals where States have expressly claimed an entitlement to a continental shelf beyond 200 nautical miles that extends within 200 nautical miles from the baseline of another State. (See paras 45-47 of Judge Tomka’s dissenting opinion, where he discusses the contrary practice of up to 20 States)

Some inconsistencies are not fatal for a recognition of general practice, as the Court held in the 1986 Nicaragua judgment (para 186). Nonetheless, in the face of directly contrary State practice of up to 20 specially affected States, can it be said that the Court correctly found the existence of a general practice? In my opinion, Judge Tomka’s dissenting opinion and Judge Hankin’s separate opinion (para 47) reach the right conclusion that there is no consistency in the practice of the States to constitute “general practice”. 

Opinio Juris

Not One and the Same

The ILC in the Draft Conclusions adopts the position that each of the two constituent elements, i.e., State practice and opinio juris, must be separately ascertained (Conclusion 3). The ILC goes on to clarify that an element’s existence cannot be deduced from the existence of the other element (page 129). This affirms the two-element approach to ascertaining customary international law, expressly endorsed by States and recognized in the Court’s previous jurisprudence.

Perhaps, the most pertinent judgment on this aspect is the Lotus case decided by the Permanent Court of International Justice (PCIJ). The PCIJ rejected to draw an inference that because States had abstained from instituting criminal proceedings against foreign ships in collision cases, a rule of customary international law had arisen that exclusively vested the jurisdiction in such cases with the flag States. The PCIJ held that mere abstentions could not establish custom for (page 28), 

only if such abstention were based on their being conscious of having a duty to abstain would it be possible to speak of an international custom.” 

The Court cited the above dictum in the Lotus decision with approval in the North Sea Continental Shelf judgment. The Court held that the mere practice of drawing boundaries according to the principle of equidistance is insufficient to establish custom without any evidence that States felt legally compelled to use the equidistance method (para 76). However, in a completely opposite manner to these decisions, the Court in this case infers the existence of opinio juris from the submissions made by States to the CLCS.  

What’s in a Motive?

The practice reflected in the submissions made to the CLCS could have easily been motivated by considerations other than a sense of legal obligation. In this regard, it is useful to quote a passage from the Court’s judgment in the North Sea Continental Shelf that (para 78),

“There is no evidence that they so acted because they felt legally compelled to draw them in this way by reason of a rule of customary law obliging them to do so-especially considering that they might have been motivated by other obvious factors.”

The present case is similar to the above decision in that there was no evidence of the motives behind States acting in a particular way and a very real possibility that such conduct was motivated by other factors. Judge Tomka points out that States may have refrained from claiming a continental shelf beyond 200 nautical miles that extends within 200 nautical miles from the baseline of another State to a) put off a diplomatic row or b) avoid the objection procedure of the CLCS (para 53).

Further, there were several instances of contrary opinio juris where States had, as a matter of right, claimed an entitlement to a continental shelf beyond 200 nautical miles that extended within 200 nautical miles of the baseline of another State (See paras 59-63 of Judge Tomka’s separate opinion). Therefore, in my opinion, considering the absence of any opinio juris in favour of the rule, the existence of other political considerations motivating such practice, and clear opinio juris to the contrary, it is difficult to consider the requirement of “accepted as law” as fulfilled. 

Possible Insights into the Court’s Methodology?

A possible explanation of ascertaining opinio juris in this manner may be discerned from Judge Iwasawa’s separate opinion. He remarks, quite interestingly, that when States abstain from acting in a manner inconsistent with their interests, it can be presumed that a sense of legal obligation motivates such abstention (para 11). However, this leads to a problematic result that a State refraining from exercising a particular right for whatever reason may end up creating a negative obligation – for its abstention can be considered as indicative of opinio juris. 

Further, several States made a similar argument in the Nuclear Weapons advisory opinion that a consistent non-utilization of nuclear weapons since 1945, which also indicates opinio juris, has crystallized a customary prohibition on the use of nuclear weapons (para 65). Nonetheless, the Court refused to find a general customary rule because of the absence of any evidence suggesting that such non-utilization of nuclear weapons was motivated by a belief of legal obligation (para 66-67). 

Judge Iwasawa provides another possible insight into the Court’s methodology when he cites the ILC’s Draft Conclusions that “the same material may be used to ascertain practice and acceptance as law”. However, the permissibility to use the same material does not equate to inferring opinio juris from that material even when there is none. The ILC is clear that two distinct inquiries are required even when using the same material, and the material will reflect opinio juris only if it indicates in some form that the particular conduct is required or permitted under customary international law (page 129).


Several decades ago, in the North Sea Continental Shelf judgment (ironically in a case concerning the delimitation of a continental shelf), the Court perhaps pronounced the most authoritative observations on identifying customary international law, even codified in ILC’s Draft Conclusions. However, in this case, the Court ignores the abundant guidance in the form of the Draft Conclusions. Or perhaps the Court felt that the circumstances of the case required a more flexible approach than the methodology prescribed in the Draft Conclusions?

At this point, it is important to briefly discuss the reaction of States to the Draft Conclusions and how it squares with the Court’s methodology. Several delegations in the discussions held in the Sixth Committee of the General Assembly reiterated the two-element approach to ascertaining customary international law. They called for a rigorous methodology to ascertain customary international law so that it is not easily created or inferred (para 131). 

Further, many delegations also expressed caution concerning the failure to react over time to a practice as evidence of opinio juris. They observed that without any express evidence of the reasoning behind refraining from reacting, such failure might simply reflect political considerations (para 133). I believe that States will find it apt to apply a similar rationale to abstaining from a particular conduct that, without evidence of the motives of a State, such abstentions could result from political expediency and not a sense of legal duty.

Lastly, an increasing number of States are approaching the ICJ that will invariably involve issues of customary international law (one that comes to mind is the alleged “terrorism exception” to sovereign immunity that Canada might claim in the Alleged Violations of State Immunities case). It will be interesting to see the Court’s methodology and approach to ascertaining customary international law in future cases. 

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