The Viability of and Need for Interpretation of Customary International Law
Whereas in the application of treaties the process of interpretation is one that always
yields a solution, with respect to CIL these rules of interpretation have not been
examined. What Pratchett and Gaiman expressed, albeit in a different context, in their
darkly humorous book Good Omens is a very apt analogy. By not knowing what the rules
that govern the interpretation of CIL are, we end up playing an ‘ineffable game of [the
judge’s/interpreter’s] own devising, which might be compared, from the perspective of any of
the other players, to being involved in an obscure and complex version of poker in a pitch-dark
room, with blank cards, for infinite stakes, with a Dealer who won’t tell you the rules, and who
smiles all the time’.
This leads to one of the following two paradoxical scenarios. Either CIL needs to be
induced each and every time, by reference to State practice and opinio juris (but this is
extremely problematic as it fails to take into account the continued existence,
development and manifestation of CIL rules); or, even worse, CIL is asserted by
international judges. But assertion, essentially means that international judges create law:
they become law-makers and exercise a power to legislate (pouvoir de légiférer) that goes
clearly against any notion of separation of powers that is so crucial to the structure of
any legal system. Both of these scenarios are untenable, so evidently there is a critical
gap in the study of CIL and in understanding how CIL can be applied in individual cases
once it has been formed. In the case of treaties, this is done through the intermediary of
This paper will have a two-pronged approach. Firstly, demonstrate that the arguments
against the interpretation of customary international law do not hold up to scrutiny.
These arguments can be grouped into three larger sets:
- It is an axiom of international law that CIL cannot be interpreted;
- CIL is not open to interpretation due to its unwritten nature;
- CIL is not open to interpretation because no court has ever undertaken
such a task.
These arguments upon closer examination will be shown to not only be demonstrably
based on false assumptions but also rejected in modern judicial practice.
The second part of this paper will elaborate on why interpretation of CIL is not only
logically and methodologically inevitable but practically also a desired option for a
plethora of reasons. Indicatively:
- The lack of an in-depth discussion on the rules of interpretation of CIL,
leaves the manner in which CIL is being identified and its content
determined couched in mystery; this raises grave concerns as to the proper
function of this source of international law, and even more perilously as to
the predictability/foreseeability of the international legal system.
- Interpretation ensures the flexibility and relevance of CIL rules,
- CIL interpretation may offer a way to address many of the concerns and
criticisms that have been launched against the rules that govern the
emergence of CIL.
Through this analysis, the paper will demonstrate that the interpretation of CIL is not
only something that is actually happening, but also a process that is inherently necessary
for the effectiveness of any legal rule, irrespective of whether it is a conventional or