According to the dualist theory, the system of International Law and Municipal Law are separate and self-contained to the extent to the rules of the one are not expressly or tacitly received into the other system. The two are separate bodies of legal norms, emerging in part, from different sources compressing different subject, and having application to different object". According to the dualist theory, Municipal Law originates in the customs and treaties between the States. Triepel, Anziloti, and Oppenheim are the chief exponent of this theory.
According to them, both these laws are different from each other because their subjects and origin are different. International Law and Municipal Law are entirely different from each other regarding their sources, subjects origin nature substance and primacy.
The sources of Municipal Law is the legislature or sovereign authority of the state, while the source of international law lies in the agreements between the two or more State. for example treaties.
See in detail >>>>> Sources of International law
Municipal Law regulates relations between the individuals under the sway of a State or between the individuals and the state, while International Law regulates the relation between the member-states of the family of nations.
Thus the subjects of Municipal Law is the individual member of that State while the subjects of international law are states.
See in detail >>>>> Subjects of International Law
International Law originates from the Common will of the States, while the Municipal Law originates from the will of the state. For example - the people.
Municipal Law -
Municipal Law is having binding force because it is given by sovereign lawmaking authority and there is a sanction behind it.
International Law -
International Law was not obligatory there is no sanction behind it.
Question of primacy -
As per Monism Theory in case of conflict International Law shall prevail because the norm of International Law is superior than the norm of Municipal Law. Whereas as per dualism theory in case of conflict between the two, Municipal Law shall prevail.
It is not correct to say that international law is binding only on the States. In modern period international law is applicable to states, individual and certain other non-state entities. It is also not correct to say that origin or source of international law is a common will of the state. there are certain fundamental principles of international law which are binding upon the states even against their will.