Sources of International Law

Note on Sources of International Law by Legum

Sources of Public International Law:

The provisions in article 38(1) of the Statute of the International Court of Justice contains some sources of International Law.

In Article 38(1), these sources are stated as follows:

The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:

(a) international conventions, whether general or particular, establishing rules expressly recognized by the contesting States;

(b) international custom, as evidence of a general practice accepted as law;

(c) the general principles of law recognized by civilized nations;

(d) subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.

International Conventions:

International conventions are taken to be treaties, defined in Article 2 of the Vienna Convention on the Law of Treaties, 1969 as "international agreement (s) concluded between States in written form and governed by international law". Similar to how a contract is formed between persons, consent is essential to be bound by the terms of a treaty. A state only becomes bound by the terms of a treaty or becomes party to a treaty if it expresses consent to be bound either by "signature, exchange of instruments constituting a treaty, ratification, acceptance, approval or accession, or by any other means if so agreed" (According to Article 10 of Vienna Convention).

Becoming party to a treaty via signature:

Whilst in the past a sovereign could merely commit a country to be part of a treaty just by signing, contemporary recognition that various consultations at the national level would have to be made before a nation becomes party to an international agreement has led to the weakening of the idea that a signature equals consent to be party to a treaty.

When the treaty explicitly says a signature means acceptance to be party to the treaty, signing nations (represented by an individual with the powers to make such commitments) may still equate an indication to be bound.

Some Effects of Signing Now:

Even if a State is not fully a party to a treaty via signing, Article 18 of the Vienna Convention still places an obligation on that state to refrain from acts that defeat the object and purpose of the signed treaty. The State, however, can opt out of this obligation if it expresses is intention not to be part of the treaty after signing.

Importantly, Article 27 of the Vienna Convention, states that a State may not "invoke the provisions of its internal law as justification for its failure to perform a treaty".

Becoming a party to a treaty via ratification:

When a nation establishes on the international plane or space its consent to be bound by a treaty, it is known as ratification. In Ghana, and prior to ratification of an international treaty, provisions in article 75 of the 1992 constitution requires that the president presents an executed treaty to parliament, parliament examines the treaty and its terms, and if satisfied, ratifies the treaty. After this local ratification, ratification would then take place at the international scene, and this usually involves a submission of the instrument of ratification to the appropriate quarters.

Acceptance or Approval:

In article 2(1)(b) of the Vienna Convention, acceptance and approval are used in the same light as ratification, and defined as “the international act so named whereby a State establishes on the international plane its consent to be bound by a treaty.” According to the United Nations glossary of terms relating to treaty action, “acceptance” and “approval” are used because “in the practice of certain states acceptance and approval have been used instead of ratification when, at a national level, constitutional law does not require the treaty to be ratified by the head of state.”


The term used when a State becomes party to a treaty it had no part in drawing up.

The second source of international law is Customary International Law: Article 38 (1)(b) of Statute of International Court of Justice:

Customary international law is characterised in article 38 as “as evidence of a general practice accepted as law”

Evidence of existence of a customary international law: According to Shaw, the following are the ways to determine if a particular practice is a customary international law.

1. The actual behaviour of states.

2. The psychological or subjective belief that such behaviour is law.

Shaw’s definition is similar to the definition established by the international court of justice in North Sea Continental Shelf Cases:

a. The act must amount to a settled practice.

b. Must be carried out in such a way to be evidence of a belief that the act or practice is made obligatory by the existence of a rule of law requiring it.

c. The states in carrying out these acts must feel they are conforming to what amounts to a legal obligation. The concept of opinio juris is often used to denote the subjective obligation or the subjective sense of obligation a State feels it has because it is bound to a particular law.

The ICJ stated that frequency of the practice is not enough to give it status of customary international law.

Problem with the above conceptualization:

To determine if a particular practice or act is done in observance of a customary international law, it is usually held that the state engaging in that practice or act ought to be doing so out of a legal obligation to the customary international law.

The difficult then is in ascertaining the convictions of a State with regards to a particular practice. Thus, are States acting the way they do simply because it is pragmatic to do so? Or are they acting the way they do in order to live up to the obligations imposed by a customary international law?

Judge Sorensen in the North Sea Continental cases advanced that it is difficult for States to obtain conclusive evidence about the motives which have prompted the actions or policies by other governments. Thus, countries cannot adequately tell if other countries are acting in accordance with the guidelines of an international custom out of a sense of obligation that they are adhering to that international custom or that they are simply being pragmatic.

Some writers have thus questioned the necessity of subjective obligation (opinio juris) in the creation of international custom because of the difficult in ascertaining whether that subjective obligation exists.

Some writers also say that evidence of repetition of precedents can be used to presume the existence of subjective obligation for States. Thus, States’ constant adherence to the terms of a purported custom can be used to presume their subjective obligation. Michael Virally similarly advances that the court is less concerned with assessing the mental states of States to determine if a subjective obligation exists, rather the court examines the facts (thus how the States act) to establish whether or not “they disclose an effective exercise by a State of a right, coupled with a recognition by another state of a corresponding obligation”.

According to article 38, the third source of international law is General Principles of Law:

According to Michael Virally, these are principle of law “so general as to apply within all systems of law that have achieved a comparable state of development". In almost all countries, the following principles usually apply:

1. Res judicata: that once an issue has been judged by a competent court, it may not be pursued further by the same parties.

2. Impartiality of judges

3. Equality before the law

4. No one may be a judge in their own case.

5. Avoidance of arbitrariness and procedural and legal transparency.

Some argue that these general principles only ought to be applied by the court if doing so is relevant and appropriate.

The final source of international law according to article 38 are the Judicial decisions and the teachings of the most highly qualified publicist:

These are considered subsidiary mans of determining rules of law. The international court of justice in adjudicating issues can rely on its own previous decisions for guidance. The teachings of publicists must come from the various nations in the world

Other sources of International Law not Mentioned in Article 38 of the ICJ Statute:

According to Dunnof et al, relying on the sources of law provided in article 38 of the Statute of the ICJ as the only sources of law leads to “an unduly static and impoverished description of international law, which can also be understood in many other ways.” Dunnof et al advanced that there the sources of international law in article 38 is only a starting point, and that there are other sources of international law not captured in article 38. These include the acts and decisions of international organizations, draft articles by the International Law Commission (this is a commission of persons with recognized competence in international law who work to develop and codify international law), and unilateral declarations, jus cogens, and the standard-setting activities of multinational corporations and non-governmental organizations.

1. Jus Cogens as a source of international law:

Jus cogens, a Latin phrase for “compelling law”, also called peremptory norms, are inalienable norms. They are defined in article 53 of the Vienna convention as norms “accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.” Thus, the norms or laws derived from jus cogens cannot be set aside. It is generally held that anything in contravention of a jus cogens shall be set aside or declared unacceptable. An analogy is the constitution which nullifies anything that goes contrary to its provisions. In article 53 of the Vienna convention on the law of treaties, it is provided that a treaty is void if it contravenes a peremptory norm or jus cogens.

Jus cogens versus Treaties:

1. Jus cogens has the “power” to render a treaty invalid if such treaty contravenes it. A treaty, however, does not necessarily have the same power. Thus, the objectives or provisions of two international treaties can be contradictory, yet each is considered valid.

2. Whilst states can decide to opt into or opt out of treaties, and not act according to the terms of the treaties, they cannot do the same for jus cogens. They are expected to act according to the principles of jus cogens norm.

Jus Cogens versus Customary International Law:

1. States can deviate from customary international law by enacting treaties which contravene the customary law, but they cannot do same for jus cogens.

2. Jus cogens has a higher level of acceptance than customary law. Jus cogens also places a higher level of obligation on states to recognize it as a fundamental overriding norm.

The next source of international law not contained in article 38 is “Acts, decisions, and resolutions of international institution”:

Britannica conceptualizes international organization as an institution that draws its membership from at least 3 states, has activity in several states, and has its members tied by a formal agreement. An example of this is the United Nations. According to Yaw Benneh, such bodies make decisions and resolutions in pursuance of powers conferred on their various organs by the member countries. Organizations such as the United Nations through declarations such as the International Declaration of Human Rights and the 1960 Declaration on the Granting of Independence to Colonial Territories and Peoples can either lead to the formation of customary international law as contained in article 38, or are themselves prove of the existence of related customary laws. Further, if the declaration or act by the international organization is consistently approved by an overwhelming majority, it may create rights and obligations for states.

Another source of international law is Unilateral acts of States (Unilateral Decisions of States to Confer Rights on Other States):

Whilst a State cannot unilaterally impose obligations upon other states without the consent of those States, a State can decide to unilaterally create rights for other states, and the right-creating state would then have an obligation to live up to the expectations it created of itself when other states decide to exercise that right. Thus, a State cannot unilaterally require another state to do something against the consent of that state to which the request is being made. But a State can say that it will do x,y,z for other states, and those other states can decide to claim that right and demand that the right-creating state lives up to their self-imposed obligation. With such acts, there must be an intention to be bound by the right-creating state.

The case of Australia versus France:

Australia initiated proceedings against France concerning the latter’s test of nuclear weapons. Whilst France challenged the juristic of the International Court of Justice to issue a ruling against it, France issue several public statements indicating its intention to halt the tests. The court found that it no longer had to rule on the case before France had created an obligation on itself to not test nuclear weapons.

Another source of international law is the draft articles of the International Law Commission:

The international Law Commission is established by the United Nations Charter in Article 12(1) and consist of people who are competent in international law. Some commentators say their publications form part of article 38 which adds the opinions of publicists as a source of international law. Some also claim the publications of the commission may also be evidence of customary law.

Another source of international law is Soft Law:

These are rules of conduct that do not themselves create legal obligations.

The Relationship between Public International Law and Domestic Law:

Two theories have been advanced to explain the relationship between international law and domestic law. These theories are monism and dualism:


This is a theory that denies the existence of difference or distinction in a particular sphere. It views international law and domestic law as “an integral part of the same system”. From a monist perspective, an international law automatically becomes part of domestic law.


This approach posits that international law is different from domestic laws. International law only becomes part of domestic law if domestic law decides to incorporate.