Public International Law distinguished from Private International Law — Public International Law Notes

Public International Law distinguished from Private International Law

Two subjects share the words “international law”, and students mix them up in a single word of an answer. But they are almost opposites: Public International Law is a law between States; Private International Law is a branch of a country’s own national law that decides which country’s law applies to a dispute between private persons. Learn the four axes of difference and you never confuse them again.

The distinction on four axes

Public International Law governs the relations between States (and other international persons). Private International Law — also called the conflict of laws — is that part of a State’s domestic law which decides, in a case with a foreign element (a contract signed abroad, a marriage between nationals of two countries), which country’s law applies and which country’s courts have jurisdiction. Distinguish them on four axes:

Source — Public IL comes from treaties, custom and general principles (international sources). Private IL comes from a State’s own municipal statutes and case law (national sources) — each country has its own rules of private international law.
Subject-matter — Public IL deals with relations between States; Private IL deals with conflicts between the laws of different countries in disputes between private persons.
Parties — In Public IL the parties are States (and organisations); in Private IL the parties are private individuals or companies.
Forum / enforcement — Public IL disputes go to the ICJ or arbitral tribunals; Private IL disputes are decided by national courts applying their own conflict rules.

A one-line memory hook: Public IL is the law above States; Private IL is a country’s internal rulebook for picking the right foreign law.

🧩 WORKED EXAMPLE — telling them apart in a problem

Facts. A French company and an Indian company dispute a contract signed in Dubai. Which “international law” governs whether Indian or French law applies?

Rule. Choosing between the laws of different countries in a private dispute is Private International Law (conflict of laws), applied by the national court seized of the case.

Apply. This is not a dispute between France and India as States, so Public IL (treaties, custom, the ICJ) does not decide it. The Indian court, if seized, applies its own private-international-law rules to choose the governing law.

Conclusion. The case is governed by Private International Law, a branch of municipal law — not by Public International Law.

flowchart LR
    A["Two 'international laws'"]
    A --> B["Public IL<br/>between States<br/>source: treaties/custom<br/>forum: ICJ"]
    A --> C["Private IL (conflict of laws)<br/>between private persons<br/>source: municipal law<br/>forum: national courts"]
    classDef box fill:#e8f0fe,stroke:#333,color:#111;
    class A,B,C box;

Case Laws

The Paquete Habana (1900) — an example of public international law (custom on prize) applied by a national court, useful to contrast with private-international-law application.

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