Customary International Law

Question 1

Definition of International Custom and source

Answer 1

Article 38(1)(b) of the ICJ Statute: International Custom as evidence of a general practice accepted as law.

Question 2

How does one determine the existence of a rule of custom?

Answer 2

It is necessary to ascertain whether there is a general practice (Usus) that is accepted as law (Opinio Juris).

Question 3

What needs to be done to determine the existence of a rule of custom

Answer 3

it is necessary to ascertain
whether there is general practice (Usus) that is accepted as law
(Opinio juris)

Question 4

Case law elaborating on the requirements of determining the existence of a rule of custom

Answer 4

Continental Shelf Case, ICJ 1985

Both requirements have been confirmed
* General practice (Usus) – Conduct element
* Accepted as law (Opinio juris) – Mental Element

Question 5

What is customary international law?

Answer 5

Customary international law consists of rules that derive from the consistent practice of States followed out of a sense of legal obligation or the behalf that those rules are legally binding (usus and opinion juris).

Question 6

Factors of customary international law

Answer 6

It is:
➢ Unwritten
➢ Universally applicable – Binding on all States
➢ Evolves over time – Progressive development of international
law
➢ Customary international law, International custom, rules of
custom

Question 7

Examples of Customary International Law = State Practice (Usus) + Accepted
as Law (Opinio juris)

Answer 7

➢ Example 1: Unwritten rules about driving on the Left Side of
the Road
▪ Usus – Everyone drives on the left side of the road = common practice (consistent and uniform)
▪ Opinio Juris – We believe that we have to drive on the left side of the road.

➢ Example 2 – Piracy
▪ Usus – States refrain from acts of Piracy
▪ Opinio Juris – States refrain from acts of Piracy because they believe that it is illegal under international law

Question 8

What is Usus?

Answer 8

➢ It is the uniform and consistent State practice.

Question 9

Examples of usus

Answer 9

➢ It can be physical practices, verbal acts, inaction

Question 10

Forms of usus

Answer 10

▪ Acts taken by states in their diplomatic relations with one another
▪ Acts taken internally by states through their legislatures or courts
▪ Acts taken by states before international organizations
▪ Deliberate inaction by states.

Question 11

Duration and consistency of practice

Answer 11

➢ State Practice Is Not Law Unless States Regard It As Law

Question 12

How long should state practice continue to qualify as usus?

Answer 12

▪ There is no rigid time element – it is determined on an ad
hoc basis.
▪ Duration not the most important component of state practice

Question 13

Anglo-Norwegian Fisheries Case, ICJ

Answer 13

There must be constant and sufficiently long practice
but also that too much importance need not be attached
to the few uncertainties or contradictions, real or
apparent that may exist in practice

Question 14

Nicaragua Case

Answer 14

▪ Absolutely rigorous conformity with the rule is not
required.

Question 15

What is the BIG rule about state practice?

Answer 15

➢ State practice is NOT customary international law, unless
States accepted/regard it as Customary international law
➢ This belief or acceptance is the opinion juris or MENTAL
ELEMENT

Question 16

What is opinion Juris?

Answer 16

➢ It is the belief that states are following a practice because they
consider it to be a legal obligation

Question 17

North Sea Continental Shelf Cases (ICJ)

Answer 17

▪ The States concerned must feel that they are conforming to what amounts to be a legal obligation.

Question 18

Case law on Treaty Participation under opinion Juris

Answer 18

▪ Nicaragua Case
* The ICJ looked at the behavior of States in treaties to assess whether they acted out of a sense of legal duty.
* The willingness of states to enter into and comply with treaties indicates that they believe in the legal obligations set out in those agreements.

Question 19

Case law on general assembly resolutions under opinio juris

Answer 19

Use of Nuclear Weapons Case (1996)

• The ICJ examined how states voted on UN resolutions to determine if they believed their actions were legally
  required.
• Consistent support for resolutions can show that States view the practice as mandatory under international law

Question 20

Relation between official publications and opinion juris

Answer 20

▪ States documents and reports that outline a State’s adherence to certain international practices can indicate
opinion juris.

Question 21

❖ How can it be proved that a State considered itself to be legally
bound?

Answer 21

▪ Through General assembly resolution, as per:
* Use of Nuclear Weapons case
* East Timor Case
* Nicaragua Case
▪ Most defining factor is the attitude of the states
concerned, whether as parties to a treaty or as
participants in a General Assembly Resolution
* Nicaragua case
▪ ICJ has also referred to major codification conventions
for the same purpose
* North Sea Continental Shelf
▪ It has also referred to the work of the ILC
* Gabcikovo-Nagymaros case

Question 22

What is the Relationship between treaty law and customary
International Law?

Answer 22

➢ To determine if a practice and its associated opinion juris have
become customary international law, it is not about a specific number of states.

Question 23

Considerations that international law follows

Answer 23

▪ Widespread and representative participation
▪ There is no rigid numerical threshold
▪ Majority participation

Question 24

The Rule of the Persistent Objector

Answer 24

▪ If a State refuses to consent to the new norm/rule of
Customary International Law, then the State will not be
bound by it.
▪ If a State can prove that it tacitly or expressly opposed a rule
of Customary International Law during the formation of the
rule then it is not bound by that rule

Question 25

Key elements of the persistent objector

Answer 25

▪ Consistent Objection
* The state must consistently object to the rule while it is emerging.
▪ Clear Communication
* The objection must be clearly communicated to other states and international bodies.
▪ Timing
* The objection must be maintained from the time the practice begins to develop into a norm.

Question 26

Norwegian fisheries case

Answer 26

In this case, a so-called ten-mile rule was not applicable to Norway as it had always opposed any attempt(s) to apply it to the Norwegian coast.

Question 27

S v Petane

Answer 27

▪ This is a South African case.
▪ The mere fact that a number of states had signed the
Protocol to the Geneva Convention, did not amount to
settled practice.

Question 28

Def of Acquiescence according to S v Pentane

Answer 28

▪ Where states take action which they declare to be legal, the inaction/silence of the other states can be used as an
expression of opinion juris.

Question 29

Gulf of Maine case

Answer 29

• Acquiescence is equal to tacit recognition, manifested by unilateral conduct which the other party may interpret as consent, and founded upon the principals of good faith and equity.

Question 30

What is the Relationship between treaty law and Customary International Law?

Answer 30

➢ Sometimes treaties codify existing rules of custom.
➢ A treaty may clarify a rule of custom that emerged prior to conclusion of the treaty.

Question 31

Jus Cogens (In Depth)
❖ Definition - Article 53 of the VCLT:

Answer 31

➢ A peremptory norm
➢ Of general international law
➢ Is a norm 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

Question 32

When will a treaty be void?

Answer 32

A treaty is void if, at the time of its conclusion, it conflicts with
a peremptory norm of general international law

Question 33

What indicates jus cogens status?

Answer 33

➢ When a norm permits no derogation (no exceptions) and has
a stringent threshold for modification or amendment.
➢ This also suggests that jus cogens norms hold a hierarchically
superior position within international law. International law recognize a hierarchy, with jus cogens at the top.
➢ Jus cogens norms are universally applicable. They are above
customary international law as they do not permit exceptions

Question 34

Right to self-determination as an example of jus cogens

Answer 34

It is:
▪ Non-derogable
▪ Stringent Modification is applicable here
▪ Universally Applicable

Question 35

What is self-determination?

Answer 35

Self-determination is a human right that grants all peoples the
freedom to determine their political status and pursue their
economic, social and cultural development without external
interference.
It is crucial for the independence of States and the
process of decolonization.

Question 36

Article 53 of the VCLT: Limitations

Answer 36

➢ Does not provide criteria for identifying jus cogens norms.
➢ Does not specificy which norms have jus cogens status.
➢ Leaves interpretation to courts (eg. ICJ), tribunals, and experts
including the International Law Commission

Question 37

What did the adoption of draft articles on jus cogens provide clarity on?

Answer 37

▪ The nature and character of jus cogens norms.
▪ The identification criteria for jus cogens norms.
▪ A non-exhaustive list of norms that have reached a jus
cogens status in international law.

Question 38

Nature of Jus Cogens

Answer 38

Jus Cogens reflect and protect fundamental values of the
international community.
They are universally applicable and
are hierarchically superior to other rules of international law.
Additionally, customary international law is the most common
basis for jus cogens

Question 39

What is the function of these fundamental values

Answer 39

➢ These fundamental values protect all individuals through the absolute prohibition of inhumane treatment

Question 40

Purpose and aim of jus cogens

Answer 40

to protect life, human dignity,
physical and mental well-being, autonomy and freedom of the
entire international communit

Question 41

Identification of Criteria for Jus Cogens

Answer 41

Whilse Article 53 of the VCLT does not explicitly outline the criteria for the identification of jus cogens norms, many States, scholars and international Law Commission have argued that
it still forms the basis for determining which norms qualify as
jus cogens.

Question 42

List the criteria met by jus cogens

Answer 42

▪ It is a norm of general international law; and
▪ It is 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

Question 43

Non-Exhaustive List of Jus Cogens Norms:

Answer 43

➢ The prohibition of aggression
➢ The prohibition of genocide
➢ The prohibition of crimes against humanity
➢ The basic rules of international humanitarian law
➢ The prohibition of racial discrimination and apartheid
➢ The prohibition of slavery
➢ The prohibition of torture
➢ The right to self-determination

Question 44

Definition of Erga Omnes

Answer 44

➢ Refers to obligations that a State has towards the international
community as a whole

Question 45

Barcelona Traction Case

Answer 45

➢ In this case, the ICJ emphasized that certain obligations are
owed ‘towards the international community as a whole and are
distinct from obligations a State owes to another State.
➢ Any State can invoke the responsibility of another State for the
breach of such obligations, even if it is not directly affected by
the violation

Question 46

Examples of erga omnes

Answer 46

➢ Prohibition of genocide
➢ Prohibition of torture
➢ Protection of fundamental human rights

Question 47

Nature of Obligations Erga Omnes

Answer 47

➢ Universal Applicability
➢ Non-Derogable
➢ Collective Responsibility

Question 48

Comparison between Erga Omnes and Jus Cogens

Answer 48

➢ Jus Cogens
▪ Not all jus cogens are erga omnes
▪ Violations of jus cogens norms invalidate any conflicting
treaties, rules of custom and other State acts.
▪ Jus cogens gives rise to obligations erga omnes.

➢ Erga Omnes
▪ Not all erga omnes are jus cogens. For example, environmental protection.
▪ Violations of obligations erga omnes can be challenged by
any State in the international community, not just by the
State directly injured by the breach.
▪ Erga omnes is triggered when jus cogens is breach/violated.