International Law and Municipal Law: Monism and Dualism

International law and municipal (national) law often govern the same matters, such as the treatment of foreigners, the sea or human rights. Two questions arise. In theory, are they parts of one legal order or two separate orders? In practice, when does a national court apply international law, and what happens when the two conflict? This note covers the theories, the rule in international law itself, and the practice of leading states, ending with India.

1. The Theories

Figure 1: Three views on the relationship

• Dualism. Triepel (1899) and Anzilotti treated the two as distinct systems: international law governs relations between states and rests on their common will, while municipal law governs individuals and rests on the will of one state; a rule of international law therefore operates within a state only if the state adopts it.
• Monism. Kelsen saw all law as one system deriving from a basic norm, with international law at the top; Lauterpacht, from a natural law view, stressed that individuals are the ultimate subjects of both systems and that international law prevails.
• Coordination theory. Fitzmaurice and Rousseau argued that the two systems do not operate in the same field and so cannot truly conflict; a state whose law departs from its obligations is not thereby invalidating its law but incurs international responsibility.
• Transformation and incorporation. Under transformation, an international rule must be enacted into national law before courts apply it; under incorporation, associated with Blackstone's statement that the law of nations is part of the law of the land, it applies automatically unless excluded by statute.

2. The View of International Law

Figure 2: International law prevails on the international plane

• Supremacy on the international plane. Before an international tribunal, national law is a fact, not a defence; the Alabama Claims arbitration (1872) held the United Kingdom liable despite the gaps in its domestic law.
• Article 27, VCLT, 1969. A party may not invoke the provisions of its internal law as justification for failure to perform a treaty.
• Article 46, VCLT. A narrow exception: a state may invoke a violation of its internal law on competence to conclude treaties only if the violation was manifest and concerned a rule of fundamental importance.
• PCIJ decisions. In Polish Nationals in Danzig (1932), a state could not rely on its constitution to avoid international obligations; in Greco-Bulgarian Communities (1930), international law prevails over municipal law between parties to a treaty.

3. State Practice

Figure 3: How four systems apply international law

• United Kingdom: custom. Customary international law is part of the common law (Buvot v Barbuit, 1737; Triquet v Bath, 1764), subject to statutes and binding precedent; in Trendtex Trading v Central Bank of Nigeria (1977), the Court of Appeal preferred incorporation, so that courts apply a changed customary rule without waiting for Parliament.
• United Kingdom: treaties. Making treaties is a prerogative of the Crown, so a treaty changes domestic law only when Parliament enacts it (The Parlement Belge, 1879; J.H. Rayner v Department of Trade, 1990); a clear statute prevails over international law (Mortensen v Peters, 1906)
• United States. International law is part of US law (The Paquete Habana, 1900); treaties are supreme law under Article VI of the Constitution, but non-self-executing treaties need legislation (Foster v Neilson, 1829; Medellín v Texas, 2008); statutes are construed, if possible, not to violate international law (Charming Betsy, 1804)
• Germany and the Netherlands. Article 25 of the German Basic Law makes general rules of international law part of federal law with priority over statutes; the Dutch Constitution allows self-executing treaties to override conflicting statutes.
• India. Customary international law is incorporated unless contrary to statute (Gramophone, 1984); treaties need legislation where they affect rights or change the law (Maganbhai, 1969); details in Topics 5 and 6.

4. Frequently Asked Questions

Can a state rely on its constitution to avoid a treaty obligation?

No. Under Article 27 of the Vienna Convention and the PCIJ opinion in Polish Nationals in Danzig (1932), internal law, including a constitution, is no justification for failing to perform an international obligation. The only exception is a manifest violation of a fundamental internal rule on treaty making competence under Article 46.

What is the difference between incorporation and transformation?

Under incorporation, a rule of international law becomes part of national law automatically and courts apply it unless a statute excludes it. Under transformation, the rule applies within the state only after it has been enacted into national law, usually by legislation.

Is India monist or dualist?

India follows the dualist approach for treaties, which need legislation where they affect rights or change the law, but applies customary international law through incorporation so long as it does not conflict with a statute or the Constitution.

5. Related Topics

• Topic 2: Is International Law True Law? The basis of obligation.
• Topic 5: International Law in India. Articles 51, 73 and 253.
• Topic 6: Treaty Making and Implementation in India. Berubari and Maganbhai Patel.