Problem 2 IEL
Learning objecti ves
1. What is customary international law?
Custom (gewoonterecht): The exact content of customary law is based on the everyday
interaction of states and therefore has the ability to adapt to changing circumstances.
It is a particularly important source of international law, many well-known legal principles
are derived from common usage and interstate practice. The way things have always been
done becomes the way that things must be done. This is because of the absence of an
international ‘law-maker’.
As a legal source, custom is controversial and volumes have been written on its theoretical
complexities.
International customary law arises when a particular way of behaving is:
1. Objective element: Followed as a general practice among states. For a specific
pattern of state behaviour to become legally binding, it must be ‘the way things are
done’. This requires consistent repetition of a particular behaviour; for a considerable
period of time states have acted in a certain manner when confronted with the same
facts. All state acts may be taken into consideration, also statement on Twitter.
- Verbal acts must be public, and internal documents and memoranda don’t qualify.
State practice can be divided into three elements:
a. Consistency: requires that practice is reasonably uniform. *Nicaragua
b. Duration: practice generally evolves slowly and gradually over time, often
through years of repeated behaviour. * North Sea Continental Shelf Cases
c. Generality: how widespread must participation in the practice be? Unanimity
is not required, but practice should include the majority of states. * North Sea
Continental Shelf Cases
2. Subjective element: requirement of opinion juris sive necessitates: only binding
when accepted by those states as legally binding, the belief that it is binding. Is
important when a state acts contrary to an existing customary rule. The purpose is to
differentiate between acts motivated by a desire to honour – or create – a legal
obligation and other acts.
The subjective element is controversial and there are theoretical difficulties in the
requirement that a state must participate in a practice believing it to be legally required.
According to the International Law Association, the existence of sufficient general and
representative state practice is usually sufficient to create a binding custom, and evidence of
opinion juris is usually only looked for if there is reason to believe that particular behaviour
stems from non-legal motivations.
A customary rule binds all states (unless a state persistently objects) including a state that
has not taken part in the information of the practice, such as a newly emerged state.
Customary legal norms need not be universal in scope.
A state may avoid being bound by an emerging customary rule by persistently objecting to
the practice. The law hereby protects a state from the imposition by a majority of other
states of new obligations upon it while simultaneously allowing that same majority to
progressively develop the law without having to wait for acceptance by all states.
, The persistent objector rule only applies, however, in relation to new and emerging
customary rules. One a rule has come into existence, it can no longer be objected to.
New states are also bound by existing customary law.
Lastly, the persistent objector rule does not apply to peremptory norms/jus cogens.
North Sea Continental Shelf Cases (Judgment of 20 February 1969)
About a rule that would have become customary law
Legal question:
What are the applicable principles and rules of international law considering the
delimination of areas of the continental shelf in this case?
Held:
The court rejected the use of the equidistance rule of delimitation as a customary rule of
international law being obligatory between Denmark, Germany and the Netherlands. It
found that there was no customary rule of international law regarding the delimitation of
the continental shelf that could be imposed on States. A delimitation should be drawn by
agreement between the States involved and in accordance with the equitable principles that
take into account the natural prolongation of land territory of States into sea.
The Court noted that ‘the passage of only a short period of time is not necessarily, in itself, a
bar to the formation of a new rule of customary law’. In situations of rapid change, state
practice may be formed in a very short time potentially paving the way for so-called ‘instant
custom’.
Example instant custom: the international reaction on 9/11; the overwhelming response to
the attacks indicated that states were suddenly willing to accept that armed attacks under
art. 51 of UN Charter could perpetrated by non-state actor.
The ICJ stated that the practice by states ‘whose interests are specially affected’ is
particularly relevant. The task is not determine how many states participate in a given
practice, but which states.
2. What is the relationship between custom and treaty?
When a treaty codifies customary international law, the parties to the treaty are bound by
both the treaty and customary law while non-parties are only bound by customary law.
In practice, all states are under the same material obligation.
The ICJ confirmed the potential existence of such ‘parallel obligations’ in *Nicaragua, where
it stated that the use of interstate force is regulated in both the UN Charter and customary
international law and that the two norms retained a separate existence.
Treaty-based obligations may also be identical to obligations in customary international law,
if the treaty has a ‘crystallizing’ effect whereby its content develops into customary law.
When the content of a treaty-based and a custom-based obligation are identical, the two
sources complement and reinforce each other. If the content of the obligations is not
identical, a potential conflict can often be avoided through interpretation.
But, if conflicting content cannot be reconciled, the question arises which of the two sources
prevails.
If one of the two has a peremptory/jus cogens character, it prevails.
Learning objecti ves
1. What is customary international law?
Custom (gewoonterecht): The exact content of customary law is based on the everyday
interaction of states and therefore has the ability to adapt to changing circumstances.
It is a particularly important source of international law, many well-known legal principles
are derived from common usage and interstate practice. The way things have always been
done becomes the way that things must be done. This is because of the absence of an
international ‘law-maker’.
As a legal source, custom is controversial and volumes have been written on its theoretical
complexities.
International customary law arises when a particular way of behaving is:
1. Objective element: Followed as a general practice among states. For a specific
pattern of state behaviour to become legally binding, it must be ‘the way things are
done’. This requires consistent repetition of a particular behaviour; for a considerable
period of time states have acted in a certain manner when confronted with the same
facts. All state acts may be taken into consideration, also statement on Twitter.
- Verbal acts must be public, and internal documents and memoranda don’t qualify.
State practice can be divided into three elements:
a. Consistency: requires that practice is reasonably uniform. *Nicaragua
b. Duration: practice generally evolves slowly and gradually over time, often
through years of repeated behaviour. * North Sea Continental Shelf Cases
c. Generality: how widespread must participation in the practice be? Unanimity
is not required, but practice should include the majority of states. * North Sea
Continental Shelf Cases
2. Subjective element: requirement of opinion juris sive necessitates: only binding
when accepted by those states as legally binding, the belief that it is binding. Is
important when a state acts contrary to an existing customary rule. The purpose is to
differentiate between acts motivated by a desire to honour – or create – a legal
obligation and other acts.
The subjective element is controversial and there are theoretical difficulties in the
requirement that a state must participate in a practice believing it to be legally required.
According to the International Law Association, the existence of sufficient general and
representative state practice is usually sufficient to create a binding custom, and evidence of
opinion juris is usually only looked for if there is reason to believe that particular behaviour
stems from non-legal motivations.
A customary rule binds all states (unless a state persistently objects) including a state that
has not taken part in the information of the practice, such as a newly emerged state.
Customary legal norms need not be universal in scope.
A state may avoid being bound by an emerging customary rule by persistently objecting to
the practice. The law hereby protects a state from the imposition by a majority of other
states of new obligations upon it while simultaneously allowing that same majority to
progressively develop the law without having to wait for acceptance by all states.
, The persistent objector rule only applies, however, in relation to new and emerging
customary rules. One a rule has come into existence, it can no longer be objected to.
New states are also bound by existing customary law.
Lastly, the persistent objector rule does not apply to peremptory norms/jus cogens.
North Sea Continental Shelf Cases (Judgment of 20 February 1969)
About a rule that would have become customary law
Legal question:
What are the applicable principles and rules of international law considering the
delimination of areas of the continental shelf in this case?
Held:
The court rejected the use of the equidistance rule of delimitation as a customary rule of
international law being obligatory between Denmark, Germany and the Netherlands. It
found that there was no customary rule of international law regarding the delimitation of
the continental shelf that could be imposed on States. A delimitation should be drawn by
agreement between the States involved and in accordance with the equitable principles that
take into account the natural prolongation of land territory of States into sea.
The Court noted that ‘the passage of only a short period of time is not necessarily, in itself, a
bar to the formation of a new rule of customary law’. In situations of rapid change, state
practice may be formed in a very short time potentially paving the way for so-called ‘instant
custom’.
Example instant custom: the international reaction on 9/11; the overwhelming response to
the attacks indicated that states were suddenly willing to accept that armed attacks under
art. 51 of UN Charter could perpetrated by non-state actor.
The ICJ stated that the practice by states ‘whose interests are specially affected’ is
particularly relevant. The task is not determine how many states participate in a given
practice, but which states.
2. What is the relationship between custom and treaty?
When a treaty codifies customary international law, the parties to the treaty are bound by
both the treaty and customary law while non-parties are only bound by customary law.
In practice, all states are under the same material obligation.
The ICJ confirmed the potential existence of such ‘parallel obligations’ in *Nicaragua, where
it stated that the use of interstate force is regulated in both the UN Charter and customary
international law and that the two norms retained a separate existence.
Treaty-based obligations may also be identical to obligations in customary international law,
if the treaty has a ‘crystallizing’ effect whereby its content develops into customary law.
When the content of a treaty-based and a custom-based obligation are identical, the two
sources complement and reinforce each other. If the content of the obligations is not
identical, a potential conflict can often be avoided through interpretation.
But, if conflicting content cannot be reconciled, the question arises which of the two sources
prevails.
If one of the two has a peremptory/jus cogens character, it prevails.
