Monism
Monists assume that the internal and international legal systems form a unity. Both national legal rules and international rules that a state has accepted， for example by way of a treaty， determine whether actions are legal or illegal. In most monist states， a distinction between international law in the form of treaties， and other international law， e.g. jus cogens is made. International law does not need to be translated into national law. The act of ratifying the international law immediately incorporates the law into national law. International law can be directly applied by a national judge， and can be directly invoked by citizens， just as if it were national law. A judge can declare a national rule invalid if itcontradicts international rules because， in some states， the latter have priority. In other states， like in Germany， treaties have the same effect as legislation， and by the principle of lex posterior， only take precedence over national legislation enacted prior to their ratification. In its most pure form， monism dictates that national law that contradicts international law is null and void， even if it predates international law， and even if it is the constitution.
Dualism
Dualists emphasize the difference between national and international law， and require the translation of the latter into the former. Without this translation， international law does not exist as law. International law has to be national law as well， or it is no law at all. If a state accepts a treaty but does not adapt its national law in order to conform to the treaty or does notcreate a national law explicitly incorporating the treaty， then it violates international law. But one cannot claim that the treaty has become part of national law. Citizens cannot rely on it and judges cannot apply it. National laws that contradict it remain in force. According to dualists， national judges never apply international law， only international law that has been translated into national law.
“International law as such can confer no rights cognizable in the municipal courts. It is only insofar as the rules of international law are recognized as included in the rules of municipal law that they are allowed in municipal courts to give rise to rights and obligations.”
The supremacy of international law is a rule in dualist systems as it is in monist systems. If international law is not directly applicable， as is the case in dualist systems， then it must be translated into national law， and existing national law that contradicts international law must be“translated away”. It must be modified or eliminated in order to conform to international law.
Examples
In some countries， such as the UK for instance， the dualist view is predominant. International law is only part of British national law once it is accepted in national law. A treaty“has no effectin municipal law until an Act of Parliamentis passed to give effect to it. In other countries thisdistinction tends to be blurred. In the vast majority of democratic countries outside the Commonwealth， the legislature， or part of the legislature， participates in the process of ratification， so that ratification becomes a legislative act， and the treaty becomes effective in international law and in municipal law simultaneously. For instance， the Constitution of the United States provides that the President“shall have power， by and with the advice and consent of the Senate， to make treaties， provided two-thirds of the Senators present concur”. Treaties ratified in accordance with the Constitution automatically become part of the municipal law of the USA”.
A matter of national legal tradition
International law does not determine which pointof view is to be preferred， monism or dualism. Every state decides for itself， according to its legal traditions. International law only requires that its rules are respected， and states are free to decide on the manner in which they want to respect these rules and make them binding on their citizens and agencies.
“The transformation of international norms into domestic law is not necessary from the point of view of international law . . . the necessity of transformation is a question of national， not of international law.”