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Nature and Definition of International Law | Law Optional Notes for UPSC PDF Download


Law serves as the foundational framework within society for establishing rights and responsibilities. In the contemporary world, there is a need for a mechanism to govern interactions between nations, and this role is fulfilled by International Law. The United Nations has developed this body of law with the primary objective of advancing international peace and security.
Nations collaborate to create legally binding regulations that they believe will serve the interests of their citizens. International Laws are designed to foster peace, justice, shared interests, and trade. States cooperate to reinforce International Law because it holds significant importance in our global society. The development of International Law is significantly shaped by the writings of legal scholars, instructions provided to diplomatic representatives, critical conventions (even those not yet ratified), and decisions made by arbitral tribunals.

Definition of International Law

According to Oppenheim, International Law can be defined as the "Law of Nations," encompassing customary laws and established rules through conventions that are recognized as obligatory by civilized States in their interactions with one another.
In essence, International Law comprises treaties, a collection of regulations, and agreements among nations that hold legal authority among them. It serves as the guiding framework for how nations are to engage with each other. International Law is especially valuable in addressing jurisdictional matters that arise in cross-border trade and interactions among different States. The fundamental aim of International Law is to advance principles of justice, peace, and mutual interests.

Relevance and Role of International Law

International Law has evolved out of necessity, expanding in tandem with increased global interactions. In today's world, International Law stands as the most practical mechanism for regulating global order. Its primary objectives encompass maintaining international peace and security, upholding fundamental rights, freedoms, and human rights, discouraging the use of threats or force by one State against the territorial integrity of another, ensuring the right to self-determination for peoples, addressing international issues through international cooperation, and advocating for peaceful methods to resolve international disputes.

Principles of International Law

International Law is founded on the following two principles:

  • Jus Gentium: These rules do not constitute a part of any formal legal statute but serve as mutually accepted norms governing the relations between two nations.
  • Jus Inter Gentes: This category pertains to treaties and agreements that are mutually recognized and accepted by both countries.

International Law provides an effective framework for the peaceful resolution of disputes. Its central focus lies in defining the rights, responsibilities, and interests of sovereign States.

Classification of International Law

International Law can be categorized into two main groups:

  • Public International Law: Public International Law is governed by treaties and universally accepted norms and customs. These norms are established through State practice and opinio juris. It regulates the interactions and relationships between nations and peoples, and those nations and peoples are bound by these legal codes and rules.
  • Private International Law: This branch of International Law focuses on resolving private disputes between individuals, rather than between States. It aims to address conflicts that extend beyond a nation's domestic jurisdiction, seeking solutions within the framework of domestic municipal law.

Sources of International Law

International Law derives from various sources, including treaties, customary practices, general principles of law recognized by civilized nations, judicial decisions, and the teachings of publicists.


Treaties are a fundamental source of International Law. They are based on the principle of pacta sunt servanda, meaning that agreements must be honored. Treaties are akin to contracts, where countries establish their rights and obligations voluntarily. Treaties outline the conduct of each State when engaging with other participating States. Various terms such as charters, declarations, conventions, and statutes are often used interchangeably with treaties, although there may be slight differences in their meanings.


Custom plays a crucial role as one of the primary sources of International Law. It is highly significant due to its decentralized nature.
Two essential conditions must be met for an action by a State to be considered custom:

  • First, there must be State practice, which does not necessarily have to be an affirmative act. State practice should be extensive, consistent, and uniform, persisting for a period sufficient to establish it as an established State action.
  • Second, there must be opinio juris, meaning the State's genuine belief that its action creates a legally binding obligation. It is important to note that not every State activity results in the creation of binding customary law. Opinio juris is essential to establish such obligations, and not all State actions necessarily reflect this belief. For instance, when a State follows a specific pattern in the General Assembly on a particular issue, it reflects the opinio juris principle.

General Principles of Law

In the realm of International Law, there is no centralized legislative body or court that can set precedents. As a result, International Law is less developed compared to Municipal Law, which governs domestic legal systems. Article 38 of the Statute of the International Court of Justice (ICJ) recognizes "general principles of law recognized by civilized nations" as a source of law in International Law.
In the Chorzow Factory Case, the Permanent Court of International Justice acknowledged the general principle of International Law, which states that a State has a duty to provide reparations when it breaches an international obligation. Similarly, in the Corfu Channel Case, the ICJ emphasized the acceptance of circumstantial evidence in legal systems and how it is acknowledged in international decisions. The principle of res judicata, meaning that a matter cannot be relitigated, is also recognized in International Law.

Judicial Decisions

As per Article 38, judicial decisions are recognized as subsidiary means of determination of law. Article 59 of the Statute of the ICJ states that the decisions of the Court can only guide them but does not have any binding value on the Court and the court is authorised to apply the previous decisions of the court which are known as the evidence of International Law. Thus, the doctrine of stare decisis is not followed in International Law.
ICJ through its case laws, advisory opinions and judges role-play a major role in the law-making process. One of the major examples of this was laid down in the case of Nicaragua vs. USA where the principle of the prohibition against the use of threat or use of force was recognised. This principle is now considered to be a part of Customary International Law.  In another case, that is, Alabama Claims arbitration, ICJ gave recognition to the peaceful settlement of international disputes. In this, judicial and arbitration methods were used in resolving conflict.

Writings of the Publicists

Article 38 also considers the teachings of highly qualified writers of International Law, such as Gentili, Grotius, and Vattel, as subsidiary means of determining law. These writers contribute to the structure and coherence of International Law through their textbooks, which offer explanations and interpretations of its principles. While their writings provide understanding, they do not create new laws; instead, they serve as evidentiary sources of law.

Is International Law Considered True Law? 

The classification of International Law as true law has been a subject of debate. Some argue in favor of its legitimacy, while others contest it. Those who view International Law as not being true law often cite its lack of certainty, stability, and predictability.

Not Considered True Law

  • John Austin, a prominent English writer on jurisprudence, asserts that International Law is not genuine law. He views it as a code of moral principles and rules of conduct without legal sanctions or a supreme legislative authority. According to Austin, International Law consists of positive international morality and opinions followed by nations based on their own discretion.
  • Hobbes and Pufendorff also contend that International Law is not true law because it lacks legal force and does not possess the command of a superior authority.
  • Holland characterizes International Law as fundamentally different from ordinary laws because it lacks the backing of a State's authority. He views it as akin to private law and suggests that it occupies a distinct position in jurisprudence.

Considered True Law

  • Hall and Lawrence argue that International Law is genuine law because it is derived from customs and precedents, serving as a source of law. They view it as a form of positive law that is routinely treated as legally binding.
  • Sir Frederick Pollock maintains that for International Law to be binding on its members, it only requires the existence of a political community and recognition by its members of established rules that bind them in that capacity. International Law fulfills these conditions.

Differences Between International Law and Municipal Law

International Law and Municipal Law differ in several ways:

  • Scope: International Law primarily governs relations between States, while Municipal Law regulates relationships between individuals and the State, as well as among individuals within a State.
  • Supremacy: In International Law, individuals are not subject to its provisions; instead, it regulates interactions between sovereign States. In contrast, Municipal Law is superior to individuals, and individuals are expected to obey it.
  • Sources: International Law derives from sources such as customs, conventions, treaties, general principles of law, judicial decisions, and teachings of qualified writers. Municipal Laws have a hierarchical structure that determines the authority of legal commandments, with higher courts' judgments holding more weight.


International Law serves as a set of rules designed to regulate the conduct of nation-States towards each other, ensuring global peace and the welfare of the international community. It plays a crucial role in resolving disputes among States and may influence domestic laws, becoming part of a country's legal framework. International Law does not always require codification into agreements, and it continues to evolve with developments in the modern world, with the International Court of Justice playing a central role in upholding its principles.

The document Nature and Definition of International Law | Law Optional Notes for UPSC is a part of the UPSC Course Law Optional Notes for UPSC.
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