Blog Series: Locating Customary International Law in the Constitutions Around the Globe

Anupa Aryal

In the previous articles of this series, we discussed about the preambles of the modern constitutions. In this article, the author has discussed the Customary International Law taking into considering the constitutions of 179 countries.

In this era of globalization, the role of International law in the municipal domain is undeniable.This relation between international law and national law is often presented as a clash of high theory, usually between monism and dualism.When we discuss these theories we confine international law to the realm of conventions, treaties, and practices of the State only. As they are the ones officially signed and ratified. But, Does Customary International law as a supreme law needs any recognition as such?  The place of customary law is necessarily an ambiguous one.

The central idea of this study is to locate the expression on ‘customary international law’ in the constitutions around the globe. Needless to say, there is no uniformity in the constitutions on the expression used to refer to the customary international law.  Some of the expressions are so nuanced that they may not fit in any of the sources of international law referred to in Article 38 of the Statute of the ICJ. This paper comparatively analyzes the term customary international law used in the constitutions globally and further deals on its recognition, acceptance, and status. It also discourses the nuanced nomenclature used for customary international law.

This paper follows an empirical study of constitutions across the world. Among 198 countries, a comparative analysis of only 179 countries is conducted. As 6 countries i.e. Canada, Israel, New Zealand, San Marino, Saudi Arabia, United Kingdom has no written constitution and data of other 13 countries i.e. Belize, Botswana, Grenada, Jamaica, Kuwait, Morocco, Nauru, North Macedonia, Samoa, Solomon Islands, Sudan, South, Trinidad and Tobago, Vatican City were not available, hence, the study of this 19 countries have been excluded.

After the empirical data was collected, sampling of 179 constitutions concerning international law was done. Out of 179 constitutions, only 19 constitutions have used the term customary international law in one or another way (discussed elaborately later). As this paper only focuses on the customary international law, thus the part regarding the general principle of law or other international law is purposefully excluded. It will be further dealt with forthcoming articles.

Article 38 of the Statute of the International Court of Justice enumerates the sources of International law. The word ‘sources’ is not mentioned in the ICJ Statute. However, expressions under Articles 38(1)(a) to (d) have been popularized as the sources of international law by various scholars and ICJ itself.The ‘customary international law’is one of the primary sources of international law. International Custom or Customary International Law (CIL) is evidence of a general practice of States accepted as law. In Nicaragua Case, the ICJ confirmed that custom is constituted by two elements: the objective element of ‘a general practice’, and the subjective element of being ‘accepted as law’, or Opinio Juris.

The explicit term of customary International law is used only by 19 constitutions, though differently. Four countries, namely,Malawi, South Africa,Zambia, and Zimbabwe have used ‘Customary International Law’, 11 countries used the term ‘universally recognized principles/ norms of international law’ which includes Andorra, Azerbaijan, Bulgaria, Georgia, Kyrgyzstan, Lithuania, Mongolia, Russia, Syrian Arab Republic, Turkmenistan, Uzbekistan. A little different from it Moldova used the term ‘unanimously recognized principles and norms of international law.’ Gambia and Swaziland used ‘general principles of customary international law’ and Nepal used the term ‘Universal Norm.’

Do all this term have the same notion of customary law? For this, we need to understand how customary law is recognized and validated. ICJ has largely remained silent on its methodology for the determination of customary international law. The legal literature has little to say on this subject[1]. There are only isolated references in the ICJ’s jurisprudence to the inductive and deductive method of law determination. The inductive method uses observable individual instances of State practice and opinio juris, whereas deductive method uses legal reasoning. However, in both stances, universal recognition is not considered necessary for a norm to become customary law. Then, will adding the term universal and unanimous before customary international law change its status? 11 countries along with Moldova and Nepal made sure to include these terms in their constitution.

Various articles have referred to the universal norm, universally recognized principles in terms of customary international law.[2] However, Universality of norms gains the status of the peremptory norm or jus cogens. A peremptory norm of general international law (jus cogens) is a norm accepted and recognized by the international community of States as a whole. Peremptory norm has its base on customary norms as well as general principles of law[3]. Jus Cogens must also satisfy the element that customary international law required. Yet, different from customary international law, they are norms that hold for all States, perhaps at all times, achieving universal binding force.[4] Hence the term universality or unanimously shall be treated as norms higher than customary international law. Adding the term universal and unanimous takes customary international law a step further, to no derogation and abidingness. However,how these constitutions wanted these terms to be interpreted needs further research.

Malawi, South Africa, and Zimbabwe share a common language stating ‘customary international law is part of National law unless inconsistent with the Constitution or an Act of Parliament’[5]. These constitutions give higher values to their national law, even over international laws customary in nature.  Zambia on other hand have limited the term to investment only, it states “Government shall not compulsorily acquire an investment, except under customary international law [Art 10 (4)],”eluding any clear understanding or status of customary international law in the national laws.

Furthermore,Gambia and Swaziland have used the term ‘general principles of customary international law’, merging two sources of international law as per ICJ Art 38 (b) and (c) i.e. Customary International law and General Principle of Law. Though ICJ mention these two as two different sources, however, the lines between them are much blurrier[6]. The ICJ in the Genocide case (Croatia v. Serbia) in 2015 enshrines principles that also forms part of customary international law. When the term merges, we should understand that the constitutions have muddied the distinction, taking general principles universally recognized as customary international law. The Gambian Constitution under Article 43 used the principle of fair trial in this regard[7]. Swaziland has further enhanced the term as accepted principles of public or customary international law, making sure both principles are elaborately highlighted, giving same stature to the general principle of international law in any international affairs and diplomacy conducted by the country, however, it shall be consistent with the national interest[8]. All these six countries have prioritized their national law over international law as well as customary norms, despite alluding respect to it.

Nepal has used the term ‘Universal Norm’ for the pursuit of an independent foreign policy, whereas Moldova has used ‘unanimously recognized principles and norms of the international law’in a generic sense, rather than unweaving its status as such.  All 11 constitutions using the term ‘universally recognized principles of international law’have a unanimous saying that these principles shall be the ‘integral part’of their legal system. As these principles cannot undergo any transformation as treaties, convention, or agreement through the legislative process, hence they directly become part of the law, irrespective of countries being monist or dualist. Out of the 11 countries constitutions of Azerbaijan, Georgia, Russia and Uzbekistan have further recognized that these principles shall be applied especially for foreign citizens and stateless persons, in terms of asylum, extradition, or any other rights, moving it further than national jurisdiction.  Bulgaria, Lithuania, Mongolia have further advanced this theory for the pursuit of foreign affairs as well. Unlike the countries only using customary international law, countries that use the expression unanimous or universal have adhered to deeper commitment, making it a direct part of their national law. 

One difference that the constitution of countries using just the term customary international law and countries using the term universally/ unanimously recognized norms of international law, is the recognition status. Constitutions that used customary international law only have given higher status to their national laws. But can national law be higher than customary international law? Yes, when the countries persistently object to it. The so-called persistent objector rule provides that, if a state objects to the establishment of a norm while it is becoming law and persistently objects up to the present, it is exempted from that norm. And as it is well known that the constitution is a strong source of evidence. Hence, directly envisaging this in the constitution can be said to have been made for persistent objection. The evidence of persistent objector, on the other hand, does not apply to peremptory norms as no derogation is permitted in jus cogens principle. Hence countries must show a deeper commitment to it. 

When 179 countries are conferring international law in their constitution, having only 19 constitutions addressing customary international law or preemptory norm is a slow pace race. One of the main reasons for this is the transformation or acceptance theory of international law. Treaties, agreements, conventions either require transformation into domestic law, or are accepted as a whole, and the constitution act as a strong medium for the furtherance of these theories. However, the same is not required for customary international law and peremptory norms. Countries that have used customary international law, seem to put it forward as a persistent objector, so as not to be bound by it and validating national law over international law including customary norms. Peremptory norms, however, have shown a strong abidingness in the constitution due to their universality and non-derogability. Concerning terminology each constitution has its way of expressing the terms, it requires intensive research to understand what the term refers to and what it wants to convey at large. However, we shall celebrate the nuanced character of each constitution in referring to international law.

Opinions expressed by the author are personal.


[1] Stefan Talmon, Determining Customary International Law: The ICJ’s Methodology between Induction, Deduction, and Assertion, The European Journal of International Law Vol. 26 no. 2, 2015, OUP

[2] Charney, Jonathan I. “Universal International Law.” The American Journal of International Law, vol. 87, no. 4, 1993, pp. 529–551. JSTOR, http://www.jstor.org/stable/2203615. Accessed 18 Apr. 2020.

[3]Lepard BD, “Defining Jus Cogens Customary Norms,” Customary International Law: A New Theory with Practical Applications (Cambridge University Press 2010)

[4] May L, “Jus Cogens Norms,” Crimes against Humanity: A Normative Account (Cambridge University Press 2004)

[5] Malawi Art 221,  south Africa Art 232,  Zimbabwe Art 326

[6]Lepard BD (ed), Reexamining Customary International Law (Cambridge University Press 2017)

[7] nothing in subsection (2) (m) shall prejudice the trial and punishment of any person for an act or omission which, at the time it was committed, was criminal according to the general principles of customary international law

[8] Swaziland shall conduct its international affairs directly or through officers of the Government per the accepted principles of public or customary international law and diplomacy in a manner consistent with the national interest.

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