In order to understand the relationship between International Law and Municipal Law, it is important to understand the similarities as well as the link between the two laws. International Law in simple term is a set of rules that comes into action when a minimum of two nation states interact. Unlike International Law, Municipal Law also known as National Law of the country applies within the domestic territory of a country.1 Article 27 of the Vienna Convention on the Law of Treaties: Prohibits the states from invoking its Municipal Law as its justification for non obligation towards the performance of treaty.

Article 8 of the Universal Declaration of Human Rights and Fundamental Freedoms:
Every individual is vested with the right to an effective remedy by the tribunal which is competent to hear, for violations of fundamental rights granted by the constitution or by any other law. 2 Municipal Law is usually argued among the nation state those who follow International Law.

Apart from the theoretical aspect the relation between the two laws there exist a practical problem in a state's Municipal courts that, as to what extent the National Court of a country give effect within its jurisdiction to the rules and principles of International Law, or which rule and principle should prevail if both the laws are in direct or indirect conflict.

Theories On The Relationship Between International Law And Municipal Law

The relationship between International Law and Municipal Law can be mainly explained by two principal theories namely Monism and Dualism. The former theory states that International Law and Municipal Law are two components but complementary to one single system. While the later states that, both the laws are entirely different, distinct and independent legal system. The dualist theory believes that state law involves the rules of a single state whereas the international law involves the legal system of a multiple states and hence this theory is sometimes known as the pluralistic theory.

To know the relationship between the two laws it is very important to understand the actual meaning of the laws. On one hand we can say that international law is "the law of the nations". On the other hand, the municipal law is known as the "internal law of the land".3

Monistic Theory

Monist theory was developed by German scholars namely Moser, Hegel, Bergbohm, Zorn, Wenzel in the late 18th century and in the 19th century by Wright, Kelsen and Duguit. It is believed that international law and municipal law are the aspects of one legal system and are not different to each other.

They are in the view that both international laws and municipal law originate from the source, branch, are facets of the same phenomenon and belongs to the unitary order comprised by the conception of law.4 But it has not clarified that about the concept of one legal system that whether it is municipal law or international law. According to the scholars both the laws in one way or the other regulate the conduct of individuals.5

• Delegation Theory:
  Monist support delegation theory which states that every state constitution has been delegated the authority in which manner the international law will apply to them. According to this theory international law will apply to municipal law without any specific delegation and this gives birth to single legal system. The theory, thus provide primacy of international law over municipal law, as it is applied immediately without any transformation.6
   
• Kelsen: Grundnorm Theory:
  Kelsen (Austrian Jurist) says that both the laws are "manifestation of a single unit of law". He also believes that since states should behave as they customarily have behaved, the international law is supreme and also because international laws represent higher authority and are derived from state's practices. According to Kelsen it becomes impossible to deny that two legal systems constitute a single system when international law is accepted that it is rules of legal character.
   
• Criticism:
  Monism is very sound theory and it is really difficult to disapprove with Kelsen view that the man is root of all laws. But in actual practice implementation of this theory is difficult because every state is a sovereign body and is not bound by international law. States obey international law only when they consent for the same or on some other account.7

Dualist Theory

The chief exponents of this theory are Anzilloti, Hersch Lauterpacht and Triepel. Dualist hold the view unlike monist, international law and municipal law are two distinct legal systems.8 To prove that both the laws are entirely different dualist gave three concepts:

1. Origin:
   municipal is at will of the state itself whereas international law is the common will of different nation states.
    
2. Subjects:
   Individuals are the subject of municipal law whereas states are the subject of international law.
    
3. Substance of their law:
   municipal law is sovereign over individuals whereas in international law no one is supreme, it's simply the sovereignty between states.9

Transformation or specific adoption theory:
Dualists believe that international law cannot be applied directly within the spheres of municipal law. The rules of former becomes applied into the later only if, transformed into municipal law. In simple words, this theory states that, no rule of international will be applied on the municipal law by its own force, unless they through the transformation theory or they are specifically adopted by the municipal courts and systems.10 This theory also marks the difference between international treaties which are promising in nature while the municipal law which the commanding in nature.11

For example international covenant on civil and political rights and international covenant on economic, social and cultural rights have been adopted by India under Protection of Human Rights Act, 1993

Criticism:
The view that international law are transformed or adopted by the municipal law is not true in absolute sense because there are some norms that are linked with the state at the will of international law

The Problem Of "Lex Posterior"

In dualist theory as already discussed, international law must be translated into municipal law and when the existing municipal law comes in conflict, the same is translated away. It simply means that international law needs to be translated into municipal law in order to conform as an international law.12 However this translation causes problem in context to the municipal law that are formed after the translation period.13

In monist theory, any municipal law that emerges after international law and the same is in conflict, municipal law becomes null and void on its own. This marks the superiority of the international law.14

So, in the dualist theory the problem of lex posterior arises which means:
The later law replaces the earlier one. This means that when international law is transformed into municipal law, it can be overridden by another municipal law on the principle of lex posterior.15 Now it becomes clear that dualist state willingly or unwillingly can violate the international law and this system requires continuous screening of all the newly passed municipal law, in order to avoid the violation of international law.16

Differences Between Monist And Dualist Theory

Monist Theory v. Dualist Theory

1. Chief supporter: Kelse--Chief supporter: Anzilotti
2. Forms a single legal system--Forms two different legal system
3. Supported by advocates of natural law--Supported by advocates of positive law
4. Exists no need for translation of laws--Exists the need for translation of laws
5. Municipal law becomes null and void if conflicted-- Municipal doesn't becomes null and void 
6. International law gets embedded automatically 17--International law does not gets embedded automatically in the municipal law. 18

Practice Of State With Reference To Indian Approach

The Indian Constitution underneath articles 51, 73, 245 and 24619 has given consideration to the term 'international laws' and 'treaties', however clause c of the article 51 (Directive Principles of the State Policy)20 mentions 'international laws' and 'treaty obligations' specifically. It should be noted that article 51(c) does not give any clear steering in context to the position of international laws in India as well as the relationship between international laws and municipal laws but we are able to gather some points from Professor C.H.

Alexandrowicz who is in the  view that the expression 'international law' in article 51 connote Customary International Law  and treaty obligation stands for treaties.21

International Customs:
In context to this India does not follow Blackstonian Doctrine which states that law of the nations is part of the law of the lands. The guiding stone of Indian practice or International custom is Article 51(c) 22of the Indian Constitution. In this regard the words of Prof. C.H. Alexandrowicz can be quoted.23 International  Custom has been shut down in India and once this approach is accepted it simply means  that customary international law is not incorporated in the Indian laws ipso facto. 24 Thus, we see that the international law has inferior position in India because it is being  incorporated in Article 51(c) which is not binding in nature.

International Treaties:
The Indian Constitution in way proclaims that International Treaties are supreme law of the law. Article 73 of the Indian Constitution states that executive power of the union would extend to law making power of the parliament whereas Article 53 states that executive power is exercised directly or indirectly by the President of India. Article 246 states that Parliament has exclusive power over union list i.e. the list 1 of the 7th schedule and entry 14 of list 1 deals with entering into treaties and agreements with foreign countries while Article 253 states that Parliament could make� laws for whole or any part of India but does not clearly points that whether enactment by Parliament is required for implementation of treaties and agreement and the question of� implementation could depend on the subject matter.25

Judicial Discourse on Relationship Between International Law and Municipal Law:

1. Shri Krishna Sharma v The State of West Bengal 26:
   In this case the Calcutta HC came up with the view that if the Indian statute are in conflict with the international law, then the Indian Courts will have to obey the law of their land. In adopting such the courts will look that such interpretation dose not comes in conflict with the rights and obligations of the International law and if such situation arises the municipal law may prevail.
    
2. ADM Jabalpur v Shivkant Shukla 27:
   After the emergency which was declared in the year 1975 under the MISA several oppositions were arrested. Justice Beg stated that UDHR is part of Indian convention and since article 21 is suspended no relief were to be provided. He also rejected UDHR being part of municipal law. Justice H.R. Khanna held his dissenting opinion and stated that when there is a conflict between the municipal law and international customary law, the court shall give municipal law. But if two interpretation of municipal law is possible the court would go for such construction that municipal law should go in harmony with the international law or treaty obligations.
    
3. Birma v State 28:
   In this case the court stated that treaties which are the part of international law don not form the part of the municipal law unless it is expressly incorporated by the legislative authority. In the mentioned case the treaty remained a treaty only and no action was taken to incorporate the same in municipal law. So, the treaty cannot be regarded as a part of municipal law.
    
4. PUCL v Union of India 29:
   In April 2001, the PUCL approached to Supreme Court on behalf of the starving people in a writ petition on the right to food. This case represents a great advance in the justice of the rights to food as human rights, as the orders of the court in this case have transformed the policy choices of the government into enforceable and justiciable rights of the people. The facts were such that the grains were kept outside while the non perishable goods were put into godown. Despite the fact that poors were unable to purchase and they were starving, though the food grain was available. After the court looked into the matter of the case poor could get the grains at subsidized rate and several acts came into force.
    
5. Vellore Citizen Welfare Forum v Union of India 30:
   Referring to the precautionary principle and the Polluter pays principle as part of the environmental law of the country, held as follows:
   Even otherwise, once these principles are accepted as part of the Customary International Law there would be no difficulty in accepting them as part of the domestic law. It is almost accepted proposition of law that the rules of Customary International Law which are not contrary to the municipal law shall be deemed to have been incorporated in the domestic law and shall be followed by the Courts of Law.
    
6. Shin Kumar Sharma & Ors. v Union of India 31:
   In this case the court held that:
   In India, treaties do not have the force of law and consequently obligations arising there from not be enforceable in Municipal Courts unless the same is backed by sanction.

Observation
Referring to above cases such as Birma v State32, PUCL v Union of India 33, Shin Kumar Sharma & Ors. v Union of India 34 etc. it can be observed that in India Courts are constant with the dualistic approach. They are simply in view that unless and until any law, treaty or custom remains untransformed in the legislation, the same cannot be enforced in the court of law.

The Supreme Court also made it clear that international customs and norms which are not contrary to the municipal law shall be deemed to have been incorporated in the domestic law. In the landmark case of Vishakha v State of Rajasthan 35 the apex court clearly stated that if there is not a law regarding any subject matter in Indian law then the reference can be taken from the customary International Law.

Conclusion
Monism and Dualism stands usually as two opposing theories of the relationship between International Law and Municipal Law. Many scholars believe that the two theories are in particular lack the explanatory provision as well as both the theories lack explanatory power and they fail to capture that exactly how the international law works within the states. Notwithstanding the statement mentioned above, both the theories monism and dualism hold power as analytical tools. With the help of these two the relationship between international law and municipal law has been examined.

References:

1. Relationship between international law and municipal law, available at: https://blog.ipleaders.in/international-law/ (visited on 28th March,2021)
2. Ibid.
3. International law and municipal law, available at: https://blog.ipleaders.in/international-law-simplified/ (Visited on 28th March, 2021)
4. Gurdip Singh, International Law 57 (Eastern Book Company, Lucknow, 3rd edn., 2015)
5. S K Kapoor, International Law 106 (Central Law Agency, Allahabad, 22nd edn., 2021)
6. Supra note 4 at 58
7. Supra note 5
8. Supra note 6
9. Dualist theory, https://repository.uchastings.edu/cgi/viewcontent.cgi?article=3097&context=hastings_law_journal (Visited on 29th March, 2021)
10. Supra note 4 at 59
11. Supra note 5 at 107
12. Supra note 1
13. Lex Posterior, available at: https://www.quimbee.com/keyterms/lex-posterior (Visited on 30th March, 2021)
14. Monism, available at: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2231530 (Visited on 30th March, 2021)
15.  Supra at 13
16. Dualist theory available at: (Visited on 30th March,2021)
17. Supra note 14
18. Supra note 16
19. The Indian Constitution, 1950
20. DPSP are the non justiciable and non enforceable parts of the Indian Constitution.
21. Professor C.H. Alexandrowicz engaged in the writing of global history of law.
22. Article 51(c) in short foster respect for international law and treaty obligations.
23. Indian approach, available at: https://lawsisto.com/artcileread/NDg3/Relationship-between-International-Law-and-Municipal-Law (Visited on 3rd April,2021)
24. Supra note 23
25. AIR 1954 Calcutta 591
26. AIR 1976 SC 470
27. AIR 1951 Raj. 127
28. AIR 1982 SC 1473
29. AIR 1982 SC 1473
30. AIR 1996 SC 2715
31. AIR 1958 Delhi 64
32. Supra note 28
33. Supra note 29
34. Supra note 31
35. AIR 1997 SC 3011