–Dr. Muhammad Abbas Mohsin, Diplomatic Advisor in the Iraqi Ministry of Foreign Affairs; Ph.D. in Public Law
The United Nations International Law Commission holds an important legal position. Its members are independent experts elected by the Sixth Committee of the United Nations General Assembly, not delegates bound by the directives of their states; and its outputs are recommendations under Article 23 of the Commission’s Statute, not treaties requiring ratification. Nevertheless, documents such as the Draft Articles on the Responsibility of States for Internationally Wrongful Acts, known by the acronym ARSIWA (2001), are routinely cited by the International Court of Justice—most notably in the Ahmadou Sadio Diallo (Republic of Guinea v. Democratic Republic of the Congo), Compensation 2012 —as if they were binding customary norms. One important question that arises concerns what happens when national constitutional courts inherit this ambiguity through their “domestic judicial practice.” The constitutional problem is this: Are the drafts and outputs of the International Law Commission considered binding customary law that is automatically incorporated into the domestic legal systems of states, or are they merely valuable scholarly writings that require domestic legislative action?
This is not merely a procedural footnote. It touches on the very heart of the question who has the authority to make customary international law binding domestically—diplomats and parliaments, or bodies of judges and experts. This article argues that national constitutional courts in Europe exercise their judicial functions and serve as essential legal filters, since the outputs of the International Law Commission are not considered binding domestic law that is automatically incorporated, because these outputs are not international treaties ratified by national parliaments, nor do they possess self-executing force ( vis obligatoria ) ; consequently, domestic constitutional courts do not treat them as legal rules that automatically take effect within the national or local legal system.
The Conceptual Ambiguity of the International Law Commission’s Outputs
The authority of the 2001 Draft Articles on State Responsibility for Internationally Wrongful Acts (ARSIWA) rests on a classificatory ambiguity that has not been fully resolved. Formally, the draft articles are considered what is known in Article 38(1)(d) of the Statute of the International Court of Justice as a “subsidiary means of determining the rules of law,” alongside legal scholars’ opinions and judicial decisions.
They serve as evidence of international custom, not as custom in and of themselves. In practice, however, decades of near-universal citation by international courts—including the International Court of Justice’s reliance on its treatment of the attribution rules in its 2022 compensation judgment Democratic Republic of the Congo v. Uganda,— has endowed the ARSIWA with a degree of influence that extends beyond its formal status.
This development blurs the line between codification (capturing existing custom in writing) and progressive development (proposing new rules that the International Law Commission deems desirable but which have not yet crystallized in state practice as international custom). The International Law Commission itself refrains from specifying, article by article, which provisions fall under which category, leaving this determination to interpreters. This deliberate ambiguity serves a functional purpose at the international level, the courts retain the authority to interpret the law, and no single court’s interpretation (of the International Law Commission’s drafts) is considered definitive. However, it becomes fraught with constitutional difficulties when applied in domestic legal systems in which constitutional preambles or substantive constitutional provisions are drafted with due regard to treaties and established custom.
The Constitutional Dilemma
Most European constitutions contain provisions that incorporate the “general rules” or “generally recognized principles” of international law directly into the domestic legal system, and these often take precedence over ordinary laws enacted by the domestic legislature. Article 25 of the German Basic Law of 1949 stipulates that the general rules of international law “form part of federal law” and take precedence over statutes. Similarly, Article 10(1) of the Italian Constitution of 1947 provides that the Italian legal system “must conform to the generally recognized principles of international law.”
The 2006 Constitution of the Republic of Serbia also contains an explicit provision that incorporates generally recognized rules of international law into the domestic legal system, while granting international treaties a higher status than ordinary laws.
All these provisions were designed for typical customary rules—such as diplomatic immunity and the prohibition of aggression—which have crystallized through the gradual accumulation of state practice and legal opinion as to their binding nature.
If a constitutional court treats provisions in draft articles prepared by the International Law Commission as automatically falling within those constitutional authorizations, it thereby combines two distinct processes of legitimization into a single judicial act.
The democratic deficit is structural
Ratification of an international treaty requires the participation of parliament precisely because it binds the state to new obligations. Consequently, customary law typically derives its legitimacy from the repeated and diverse practices of the states themselves in their capacity as legislative bodies.
A draft of the International Law Commission, by contrast, is the product of the Commission’s sixty experts; however distinguished they may be, they deliberate without a mandate to bind any other party, particularly the domestic legal systems and judiciaries of states.
When a constitutional court elevates the work of the International Law Commission regarding codification to the status of custom as provided for in Article 25 of the German Basic Law, for example, it effectively delegates a quasi-legislative function to the Committee on International Law, thereby bypassing the domestic legislature, which would normally scrutinize any new international obligation. This constitutes a unique form of friction in the separation of powers: not the usurpation by domestic constitutional courts of the legislature’s role in enacting laws, but rather the courts’ use of a fundamental constitutional provision to legitimize the output of an unelected international body, without consulting the legislature at all.
The Judicial Filter: European Courts and the Treatment of the Outputs of the International Law Commission
European courts have generally resisted the temptation to overreach, treating the outputs of the International Law Commission as guidance rather than binding rulings. The decision in the Argentine Necessity Case (Decision of the German Federal Constitutional Court of May 8, 2007) serves as an illustrative example.
In that decision, the German Federal Constitutional Court considered whether Argentina could invoke necessity under public international law as an affirmative defense against lawsuits filed in German courts by individuals due to the country’s default on sovereign bonds in early 2002. The Court acknowledged that necessity is recognized in customary international law as a ground for negating the illegality of a breach of an international obligation. It also accepted that Article 25 of the 2001 Draft Articles of the International Law Commission constituted an appropriate codification of that customary international law.
Consider also the historic ruling of the Italian Constitutional Court, No. 238/2014 (October 22, 2014). After the International Court of Justice ruled in the case concerning State Immunity (Germany v. Italy) in 2012 that Italy had violated customary international law by allowing its courts to hear claims for compensation against Germany for crimes committed by Nazi forces during World War II, the Italian Parliament enacted Law No. 5 of 2013. This law required Italian judges to refrain from exercising their jurisdiction in such cases and opened the door to the reconsideration of final judgments rendered against Germany.
The Florence Court referred the question of the constitutionality of this law to the Italian Constitutional Court, and also queried the constitutionality of the rule of customary international law regarding state immunity on the grounds that it conflicts with the right to access to justice (Article 24 of the Constitution) and inviolable rights (Article 2 of the Constitution).
The Italian Constitutional Court ruled that the customary international rule granting states immunity for their sovereign acts had not, in fact, been incorporated into the Italian legal system. It reasoned that this rule, as interpreted by the International Court of Justice (i.e., that it extends even to war crimes and crimes against humanity), conflicts with the supreme principles of the Italian constitutional order, specifically the right of access to the courts (Article 24) and the inviolable rights (Article 2). Article 10(1) of the Constitution, which automatically incorporates international customary law, applies subject to the condition that such customary law does not conflict with these supreme constitutional principles. Consequently, the Italian Constitutional Court held that the rule had not been incorporated into the Italian legal system; it is “non-existent” within it.
The Court’s reasoning confirms that even well-established customary law can be subjected to a test of constitutional compatibility; a fortiori, controversial draft laws on international law or those concerned solely with codification cannot expect a smooth transition into the legal system.
Turning to the United Kingdom, although British practice is dualistic in nature, it demonstrates a convergence on this point. In Jones v. the Home Secretary ([2006] UKHL 26), the House of Lords extensively discussed the International Law Commission’s articles on state immunity and responsibility, affirming that customary international law is incorporated into common law only if it is “clearly established” —a standard that the House of Lords considered to go beyond what the International Law Commission’s reformulation alone could provide.
The subsequent decision of the UK Supreme Court in Benkharbouche v. Secretary of State for Foreign and Commonwealth Affairs ([2017] UKSC 62) continued this approach of using the relevant ILC codes as an interpretive re within the United Kingdom
Constitutional Foundations and the Judicial Function
These cases clearly reveal a coherent, albeit implicit, principle: constitutional courts across various traditions—from Germany and Italy to the British dualist system—agree that the outputs of the International Law Commission are an important subsidiary source of law with high authority, rather than law in force in and of itself. This is the “constitutional foundation of international law,” which operates within a more cautious framework. Rather than simply accepting that domestic law is automatically subject to international norms, national constitutional courts act as filters, testing proposed customary rules against the constitutional framework before accepting them. The ILC’s drafts make a significant contribution to this inquiry—by formulating arguments, identifying issues, and providing legal terminology—without supplanting the conclusions of independent courts regarding legal opinion and national practice, or the legislative branch’s authority to assume genuine new obligations.
Conclusion
The apparent European consensus on this matter—as reflected in the rulings of Karlsruhe and London, alongside the broader constitutional safeguards in Rome—is neither one of full incorporation nor of outright rejection.
The drafts of the International Law Commission are considered exceptionally persuasive evidence in the context of identifying and codifying customary legal rules, as national courts themselves insist on this procedure, thereby preserving the constitutional boundaries between judicial recognition of existing international custom and the incorporation of new international obligations into domestic law. This is a true comparative achievement: unilateral and bilateral systems, as well as courts bound by the constraints of statutory law and those committed to the incorporation of public international law, achieve a similar functional balance through different jurisprudential paths. Whether this delicate balance will withstand the upcoming major projects of the International Law Commission—on sea-level rise and state formation, or on crimes against humanity—will test the ability of constitutional courts (the guardians of the European constitution) to maintain this discipline as the International Law Commission’s outputs become increasingly ambitious, and as pressure mounts on domestic courts to treat the codification of international experts as a shortcut to circumvent the more difficult task of establishing genuine state consent.
Suggested citation: Mohammed Abbas Mohsin, The European Reception of ILC Outputs: Non-Treaty Law in Domestic Courts, Int’l J. Const. L. Blog, Aug. 29, 2026, at: http://www.iconnectblog.com/the-european-reception-of-ilc-outputs-non-treaty-law-in-domestic-courts/
