Custom in international law

In any primitive society certain rules of behaviour emerge and prescribe
what is permitted and what is not. Such rules develop almost subconsciously
within the group and are maintained by the members of the
group by social pressures and with the aid of various other more tangible
implements. They are not, at least in the early stages, written down or
codified, and survive ultimately because of what can be called an aura of
historical legitimacy.8 As the community develops it will modernise its code of behaviour by the creation of legal machinery, such as courts and
legislature. Custom, for this is how the original process can be described,
remains and may also continue to evolve.9 It is regarded as an authentic
expression of the needs and values of the community at any given time.
Custom within contemporary legal systems, particularly in the developed
world, is relatively cumbersome and unimportant and often of only
nostalgic value.10 In international law on the other hand it is a dynamic
source of law in the light of the nature of the international system and its
lack of centralised government organs.
The existence of customary rules can be deduced from the practice
and behaviour of states and this is where the problems begin. How can
one tell when a particular line of action adopted by a state reflects a legal
rule or is merely prompted by, for example, courtesy? Indeed, how can
one discover what precisely a state is doing or why, since there is no living
‘state’ but rather thousands of officials in scores of departments exercising
governmental functions? Other issues concern the speed of creation of
new rules and the effect of protests.
There are disagreements as to the value of a customary system in international
law. Some writers deny that custom can be significant today
as a source of law, noting that it is too clumsy and slow-moving to accommodate
the evolution of international law any more,11 while others
declare that it is a dynamic process of law creation and more important
than treaties since it is of universal application.12 Another view recognises
that custom is of value since it is activated by spontaneous behaviour and
thus mirrors the contemporary concerns of society. However, since international
law now has to contend with a massive increase in the pace and
variety of state activities as well as having to come to terms with many
different cultural and political traditions, the role of custom is perceived
to be much diminished. There are elements of truth in each of these approaches. Amidst a wide
variety of conflicting behaviour, it is not easy to isolate the emergence of
a new rule of customary law and there are immense problems involved in
collating all the necessary information. It is not always the best instrument
available for the regulation of complex issues that arise in world affairs,
but in particular situations it may meet the contingencies of modern life.
As will be seen, it is possible to point to something called ‘instant’ customary
lawin certain circumstances that can prescribe valid ruleswithout
having to undergo a long period of gestation, and custom can and often
does dovetail neatly within the complicated mechanisms now operating
for the identification and progressive development of the principles of
international law.
More than that, custom does mirror the characteristics of the decentralised
international system. It is democratic in that all states may share
in the formulation of new rules, though the precept that some are more