How to use this visual guide
Amber = memory hook — learn the keywords
Green = exam tip — what scores marks
Blue dashed = simple diagram to redraw in exam
Pink = case law citation details
1 Nature of IL — Is it a True Law?
International Law (IL) is the body of rules governing relations between States, international organisations, and individuals. It rests on consent rather than a supreme global sovereign, sparking the classic debate: is it truly law?
Austin's attack — "It is not law, only Positive International Morality"
Austin's definition of law"Law is the command of a sovereign backed by sanctions." Every law needs a Sovereign, a Command, a Duty and a Sanction.
- No sovereign — there is no world government or parliament above States.
- No effective sanctions — no world police or compulsory court.
- Therefore IL is (for Austin) mere positive morality, not law.
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Memory trick — Austin's 4 essentials
S · C · D · S → "Some Cops Demand Silence"
Sovereign · Command · Duty · Sanction. Austin says IL fails all four.
Sovereign · Command · Duty · Sanction. Austin says IL fails all four.
Modern view — IL IS true law (reply to Austin)
- Austin's command theory is too narrow — even domestic law (like customs) isn't just "commands."
- IL does have sanctions: reprisals, countermeasures, loss of rights, and UN Security Council action.
- States treat it as binding — they argue over legal interpretations, not whether law exists.
- Modern jurists (Oppenheim, Starke, Kelsen) firmly classify IL as law.
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Exam tip
Structure: (1) Austin's theory → (2) his 3 reasons IL fails → (3) 4–5 counter-arguments → (4) conclude: IL is a "weak" but genuine legal system. Always cite the S-C-D-S framework.
2 Definition of International Law
Oppenheim (classic, State-only)"Law of Nations… the body of customary and treaty rules considered legally binding by civilised States in their intercourse with each other."
Starke (modern, wider)IL includes rules States feel bound to observe plus rules on international institutions, and relations of States with individuals.
- Fenwick: general principles + specific rules binding on members of the international community.
- Shift over time: States-only → States + Organisations + Individuals.
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Remember the 3 "actors" of modern IL
S-I-O → "State, Individual, Organisation" — the widening circle of subjects.
3 Public IL vs Private IL (Conflict of Laws)
Both use the word "international," but they are fundamentally different. Private IL is a branch of a country's domestic law that decides which law/court applies when a dispute has a foreign element.
| Basis | Public International Law | Private International Law |
|---|---|---|
| Nature | Autonomous international legal system | Part of each State's domestic law |
| Subjects | States & organisations (individuals limited) | Private individuals & companies |
| Source | Treaties, custom, general principles | Domestic statutes & case law |
| Subject matter | Sovereignty, treaties, war, sea, human rights | Contract, tort, marriage, succession w/ foreign element |
4 Origin & Development of IL
- Ancient: Egypt–Hittite treaty (c.1258 BC, earliest treaty); India's Kautilya's Arthashastra; Greece's Amphictyonic Councils; Rome's jus gentium.
- Medieval: Canon Law; "Just War" (Aquinas); maritime codes (Consolato del Mare).
- Founding: Hugo Grotius (1583–1645) — "Father of International Law," wrote De Jure Belli ac Pacis (1625).
- Modern: Peace of Westphalia 1648 (birth of sovereign-State system) → UN Charter 1945.
✏️ Draw this — the timeline arrow
5 Basis of IL — Why does it bind States?
| Theory | Jurists | Binding force comes from… |
|---|---|---|
| Naturalist | Grotius, Vitoria, Pufendorf | Natural law / universal reason — binds whether or not State consents |
| Positivist (consent) | Bynkershoek, Vattel | State consent — express or implied |
| → Common Will | Triepel | Union of wills = Gemeinwille (Vereinbarung) |
| → Auto-limitation | Jellinek | State's own self-limitation of its will |
| → Pacta sunt servanda | Anzilotti | One basic norm: agreements must be kept |
| Grundnorm | Kelsen (Pure Theory) | A hypothetical basic norm at the top of a hierarchy of norms |
6 Sources of IL — Article 38(1) ICJ Statute
The authoritative list of sources applied by the International Court of Justice:
| Clause | Source | Rank |
|---|---|---|
| 38(1)(a) | International conventions / Treaties | PRIMARY |
| 38(1)(b) | International custom (practice accepted as law) | |
| 38(1)(c) | General principles recognised by civilised nations | |
| 38(1)(d) | Judicial decisions & juristic writings | SUBSIDIARY |
Art 38(2) — The Court may also decide ex aequo et bono (what is fair and good) only if both parties agree.
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The master mnemonic
"Tiny Cats Grab Juicy Jerky"
Treaties · Custom · General principles · Judicial decisions · Juristic writings.
Treaties · Custom · General principles · Judicial decisions · Juristic writings.
✏️ Draw this — Sources tree diagram
7 Custom as a Source
Custom = general practice of States followed out of a sense of legal duty. Two ingredients are essential:
✏️ Draw this — the custom "equation"
"Body + Soul." Practice without belief = mere usage/comity, not law.
⚖️ Case Law
North Sea Continental Shelf Cases (1969)
FactsGermany challenged Denmark/Netherlands regarding boundary delimitation using the 'equidistance' rule from a treaty Germany had not ratified.
HeldCustom needs extensive & virtually uniform practice + opinio juris. The equidistance rule was not a customary rule.
⚖️ Case Law
The Paquete Habana (US Sup. Ct., 1900)
FactsUS Navy seized two unarmed Cuban fishing boats as prize of war.
HeldCustom exempting coastal fishing vessels is part of international law, which US courts must enforce.
8 Relationship: IL & Municipal (Domestic) Law
| Basis | Municipal Law | International Law |
|---|---|---|
| Subjects | Individuals/entities in the State | Mainly States (+ orgs, individuals) |
| Source | State Legislature | Treaties, custom, general principles |
| Structure | Vertical — sovereign over subject | Horizontal — equal sovereign States |
| Enforcement | Courts & police | State responsibility, reciprocity, institutions |
✏️ Draw this — one legal order vs two separate
Dualism = two circles apart. Monism = one big circle.