International Law 2025 – Lecture 1 Notes: Customary International Law

Foundations of Public International Law (PIL)

• Harvard definition (Damrosch, Henkin & Murphy): “Law that principally operates among sovereign states, arising from sources such as treaties and the customary practice of states.”

• Three analytic pillars derived from sentence:

  1. Actors (“principally states”).

  2. Sources (“treaties & custom”).

  3. Legal character (“is law” vs mere politics).

What PIL is Not

• Comparative Law – juxtaposition of municipal systems.

• Private International Law (Conflict of Laws) – forum & choice-of-law for private disputes (e.g., collision of Bolivian & Panamanian ships).

Law vs Politics

• Political motives create law, but adjudication requires legal vocabulary.

• Henkin Compliance Maxim (1979): “Almost all nations observe almost all principles of international law … almost all of the time.”

• Decentralised “primitive” system (no legislature; ICJ jurisdiction consensual) yet still binding.

Actors in the International System

• States (primary subjects):
  • Sovereign equality (UN Charter Art. 2(1)); unrestricted capacity unless limited by law.

• Other Entities with International Personality:
  • Intergovernmental Organisations – UN, WHO, UNESCO, NATO, EU, AU, Commonwealth.
  • Specialised Agencies & Programs – ILO, UN Secretariat, Peacekeeping DPKO.
  • Humanitarian bodies – ICRC (powers under 1949 Geneva Conventions, e.g., GC III Art. 126 POW visits).
  • International Tribunals – ICJ (The Hague), ICC (The Hague), ITLOS (Hamburg), ICTY/ICTR, ad hoc inquiries.
  • Corporations (e.g., Cluster-Munitions Convention restricts private investment).
  • Individuals (limited standing; ICCPR + First Optional Protocol enables communications to UN HRC – Toonen v Australia re Tasmanian anti-sodomy law).

Sovereignty & Statehood

• Lotus Principle (PCIJ 1927): “Restrictions upon the independence of states cannot be presumed.”
  • Revived caveats: modern law curtails absolute sovereignty; $\textit{jus cogens}$ norms (e.g., genocide, racial discrimination, aggressive war) non-derogable.

• Montevideo Convention 1933 (customary status) enumerates four statehood criteria:

  1. Permanent population.

  2. Defined territory.

  3. Government.

  4. Capacity to enter relations with other states.

• Political stakes: Palestine, Taiwan, etc. Recognition vs declaratory efficacy.

Sources of International Law (ICJ Statute Art 38(1))

1. Treaties – express consent; analogous to statutes.

2. Customary International Law (CIL) – state practice + opinio juris.

3. General Principles of Law recognised by civilised nations.

4. Subsidiary Means: judicial decisions & “teachings of the most highly qualified publicists”.

Customary International Law – Detailed Analysis

Essential Elements

• State Practice (usus)
  • Must be extensive & substantially uniform (North Sea Continental Shelf 1969).
  • Quality over quantity: conduct of “specially affected” states weighs heavily.
  • Attributable only when performed by state organs (executive, legislature, judiciary, authorised military/diplomats).

• Opinio Juris
  • Belief that practice is legally obligatory, not mere courtesy.
  • Evidenced via: statements in GA, treaties’ preambles, ministerial speeches, pleadings before courts, military manuals.

Binding Effect & Consent

• Silent acquiescence ⇒ consent ⇒ bound.

• Persistent Objector Rule: state that consistently & openly rejects emerging rule during formation remains unbound (Anglo-Norwegian Fisheries 1951).

• Regional / Local Custom: binding inter se among limited group (Right of Passage over Indian Territory 1960).

Special Phenomena

• Instant Custom: near-uniform acceptance of new practice in very short time (e.g., $1957$ Sputnik orbital overflight ⇒ freedom of outer space).

• Jus Cogens vs Custom: peremptory norms override conflicting custom or treaties.

Proving CIL (Evidentiary Sources)

• UN GA & Security Council resolutions (voting patterns + debate transcripts).

• Diplomatic correspondence, treaties (ratifications can indicate but not create CIL), national legislation, executive orders.

• Domestic & international judicial decisions.

• Official military/diplomatic manuals (e.g., U.S. DoD Law of War Manual, Australian Targeting DMP).

• ILC Draft Articles & commentaries (secondary but persuasive).

Landmark Jurisprudence

• Nicaragua v United States (ICJ 1986):
  • Affirmed existence of CIL prohibitions on use of force & intervention.
  • Stated perfect consistency unnecessary; general conformity suffices.
  • Permitted reliance on GA resolutions, treaty ratifications & ILC work as evidence of CIL.

• Paquete Habana (U.S. Sup. Ct 1900): $\approx1000$ pages; traced centuries of practice to find fishing vessels immune from capture.

• Lotus (PCIJ 1927) – freedom principle absent prohibitive rule.

• North Sea Continental Shelf (ICJ 1969) – need for widespread & representative participation.

Treaties ↔ Custom Interplay (Preview)

• Treaties can:
  • Codify existing custom.
  • Crystallise emerging custom (mass ratification → CIL for non-parties).
  • Co-exist distinctly (non-parties unaffected unless CIL develops).

• Vienna Convention on the Law of Treaties (VCLT 1969) rules on interpretation (Art 31) to be covered next week.

Study & Exam Tips (Lessons from 13 Years)

• Start early; “Week 11 time-machine problem” unsolvable.

• Focus on law, not pure IR politics (e.g., the Palestine essay that cited zero law = fail).

• Always provide legal basis: treaty article, CIL evidence, or case law.

• Use Nicaragua where truly relevant (but not as generic filler).

• Check spellings: $\textit{opinio juris}$ NOT opinion juris (auto-correct hazard).

• In footnoting count, apply AGLC4; confirm all citations in provided guide.

Numeric & Formulaic References

• Word limit: $2000$ (inc. footnotes).

• Late penalty: $5\%/\text{day}$.

• Quiz average completion: $\approx45\ \text{min}$.

• Exam weighting equation (see Assessment supra).

• ICJ Statute Art 38(1) lists $3$ primary + $2$ subsidiary sources.

Ethical & Real-World Implications

• Academic dishonesty recorded → communicated to Supreme Court on admission; jeopardises “fit & proper person” test.

• IL constantly evolves (expect in-semester developments).

• Practical stakes: navigational rights in Indo-Pacific, use of force debates (Ukraine, etc.), treaty-based business compliance (super funds & cluster-munitions ban).

Key Terminology Cheat-Sheet

• AGLC4 – citation standard.

• CIL – customary international law (state practice + opinio juris).

• Persistent Objector – state exempt from new CIL due to continuous objection.

• $jus\ cogens$ – peremptory norm; non-derogable.

• Montevideo 1933 – statehood test.

• Lotus Freedom – “not prohibited = permitted”.

• Article 38(1) – ICJ source hierarchy.

• VCLT 1969 – treaty interpretation framework.