Problem 2
What is customary international law?
The absence of an international ‘law-maker’ has made custom an important source of
international law and many well-known legal principles and rules are derived from custom.
International customary law arises when a particular way of behaving is:
1. Followed as a general practice among states (objective element)
2. Accepted by those states as legally binding (subjective element)
A customary rule binds all states, even the ones that did not take part in the formation of the
practice, unless a state persistently objects to such rule. Customarily international law can
also develop regionally between a particular group of states.
The objective element
Before a specific pattern of state behaviour becomes legally binding, it must be ‘the way
things are done’. This requires a consistent repetition of a particular behaviour or act.
What counts as an act? Both physical acts (e.g., conduct of a military operation) and verbal
acts (e.g., diplomatic statement, press release etc.) count as acts, but verbal acts must be
public. Internal documents for example do not count as an act.
State practice can be divided into three elements:
1. Consistency
2. Duration
3. Generality
Consistency requires a practice to be reasonably uniform and constant. In Nicaragua is
stated that it is not expected that states act with complete consistence. As long as the
practice is generally consistent with the rule and inconsistency is by and large treated as a
breach of the rule, rather than recognition of the rule, the conduct may suffice.
For duration, practice generally evolves slowly and gradually over time, often through years
of repeated behaviour. The ICJ stated in the North Sea Continental Shelf Cases, the passage
of only a short period in 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 the creation of so-called ‘instant custom’, for instance after the 9/11
attacks.
Generality means that the majority of states should participate in practice of the custom,
but unanimity is not required. In the North Sea Continental Shelf Cases was determined that
the practice by states whose interests are specially affected is most relevant.
What is customary international law?
The absence of an international ‘law-maker’ has made custom an important source of
international law and many well-known legal principles and rules are derived from custom.
International customary law arises when a particular way of behaving is:
1. Followed as a general practice among states (objective element)
2. Accepted by those states as legally binding (subjective element)
A customary rule binds all states, even the ones that did not take part in the formation of the
practice, unless a state persistently objects to such rule. Customarily international law can
also develop regionally between a particular group of states.
The objective element
Before a specific pattern of state behaviour becomes legally binding, it must be ‘the way
things are done’. This requires a consistent repetition of a particular behaviour or act.
What counts as an act? Both physical acts (e.g., conduct of a military operation) and verbal
acts (e.g., diplomatic statement, press release etc.) count as acts, but verbal acts must be
public. Internal documents for example do not count as an act.
State practice can be divided into three elements:
1. Consistency
2. Duration
3. Generality
Consistency requires a practice to be reasonably uniform and constant. In Nicaragua is
stated that it is not expected that states act with complete consistence. As long as the
practice is generally consistent with the rule and inconsistency is by and large treated as a
breach of the rule, rather than recognition of the rule, the conduct may suffice.
For duration, practice generally evolves slowly and gradually over time, often through years
of repeated behaviour. The ICJ stated in the North Sea Continental Shelf Cases, the passage
of only a short period in 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 the creation of so-called ‘instant custom’, for instance after the 9/11
attacks.
Generality means that the majority of states should participate in practice of the custom,
but unanimity is not required. In the North Sea Continental Shelf Cases was determined that
the practice by states whose interests are specially affected is most relevant.
