With regard to the question of the relationship between International Law and municipal law, the theoretical question is whether International Law and municipal law are part of a single legal order or they are comprised of two distinct systems of law.
The question above raises further questions, namely;
the status of rules of municipal law before international tribunals
The circumstances in which rules of public International Law will be applied by a municipal court, and
What happens if a rule of municipal law is in conflict with a rule of International Law?
Here you will find answers to those questions.
The Relationship between International Law and Municipal Law
There are two doctrines that have sought to clarify the relationship between municipal law and international law. These doctrines are referred to as monism and dualism. Monism entails that, international law and municipal law are both parts of a single legal structure while dualism presupposes that international law and municipal law are separate systems.
Monism is an international law doctrine that explains the relationship between municipal law and international law. This doctrine holds that International Law and municipal law are both parts of a single legal structure. Thus the monist considers the municipal law and international law to operate within a common field and to be concerned with the same subject matter.
With monism, if there is a conflict between municipal law and international law, then the rules of International Law shall prevail.
Further, in the monist practice, once a treaty is, signed it becomes part of the law of the land immediately and automatically.
Dualism is also an international law doctrine that explains the relationship between municipal law and international law. The dualists argue that International Law and municipal law are separate systems whereby international law regulates relations between states, while municipal law regulates relations between the state and its citizens.
With Dualism International Law operates in the municipal sphere only when there is a specific act to adopt the law and in case of conflict between the two, municipal law can give effect to International Law.
Application of Municipal Law in International Courts and Tribunals
It is well settled in international law that the judgments of a national court may constitute a source of International Law. While this is the case, the general rule is that the state may not rely upon a provision of municipal law as an excuse for a breach of international obligations.
Article 27 of the Vienna Convention on the Law of Treaties (1969) provides that, a party may not involve the provisions of its internal law as justification for its failure to perform a treaty. Therefore, obligations arising under International Law prevail over municipal law.
Therefore states must ensure that their domestic legislation is in line with international obligations.
Application of International Law in Municipal Courts
The status and treatment of International Law in municipal courts differs from state to state. The starting point is the constitutional arrangement of a particular state regarding the application of international law in their state.
In the legal system of a county, it is usually stated how International Law is to be treated by the courts of that state.
Generally, there are two doctrines that explain the application of international law in municipal courts i.e. the doctrine of incorporation and the doctrine of transformation.
The Doctrine of Incorporation
The doctrine of incorporation holds that International Law is automatically part of municipal law, without any express act of adoption. In such a situation, a treaty signed and ratified by a state would become binding on the citizen of that state, without any legislation being passed. As such in some states, the constitution of the state will provide that rules of International Law should become automatically part of municipal law.
In principle, The doctrine of Incorporation follows the monist approach.
Doctrine of Transformation
The doctrine of transformation holds that the rules of International Law do not become part of municipal law, unless and until there has been an express act of adoption. Therefore, a rule of International Law must be transformed into domestic law.
Thus, if a state has entered into a treaty, that instrument would not be given effect to in the courts of the state, unless domestic legislation had been enacted to transform it into municipal law.
The Doctrine of Transformation follows the dualist approach.
Read also: Main sources of Public International law
SHAW MALCOLM, International Law, 5thEdition, Cambridge University Press, 2005.
BROWNLIE IAN, Principles of Public International Law, 5thEdition, Oxford University Press, 2001.
STARKE, J. G., Introduction to International Law, London, Butterworths, 1989