Customary International Law
| Author | John H. Currie |
| Profession | Faculty of Law University of Ottawa |
| Pages | 160-192 |
CHAPTER
CUSTOMARY
INTERNATIONAL
LAW
A.
NATURE
AND
ELEMENTS
OF
CUSTOMARY
INTERNATIONAL
LAW
1)
Nature
of
Customary International
Law
Recalling
the
largely anarchic state
of the
international legal system
and
the
resulting conundrum
of how to
"make" (or,
for
natural lawyers,
how to
"discover") international law,
one
solution might
be to
borrow
a
page
from
domestic legal systems
which
sometimes treat certain
habitual
or
customary societal practices
as
evidence
of a
form
of
law.
For
example,
the
modern common
law
system could
be
considered
such
a
form
of
"customary"
law in
that
it
represents
the
cumulative
and
generally consistent practice
of a
certain
set of
actors (namely, judges)
over
time.1
Moreover, such practice
is
"self-conscious"
in
that these
actors subjectively believe (for whatever reason) that their
consistent
practice
is
required
as a
matter
of law
(usually expressed
as the
rule
of
stare
decisis).
That
is,
common
law
judges would
not
explain their pat-
tern
of
deciding like cases alike
as a
random
or
merely practical phe-
1 On the
similarity between customary
legal
systems
and the
common
law
tradition,
see
J.L.
Brierly,
The Law
of
Nations:
An
Introduction
to the
International
Law of
Peace,
6th ed. by H.
Waldock
(Oxford:
Clarendon Press, 1963)
at 70.
160
5
Customary
International
Law 161
nomenon,
but
would rather consider their consistent practice
to be
legally
required.2
The
apparent circularity
of
such
a
customary system
of law
(con-
duct
is
legally required because
it is
regularly engaged
in and
believed
to
be
legally required)
is in
fact
well
suited
to an
international
society
composed
of
sovereign entities.
The
theory requires
no
legislator
but
rather derives
the law
from
the
consistent actions
and
subjective con-
victions
or
perceptions
of its own
subjects.
Superficially
such
a
source
of law
would also appear
to be
conso-
nant with
the
positivist theory
of
consent, particularly
if
consistent
practice
and
subjective belief
are
considered law-creating rather than
simply law-evidencing. That
is,
states which consistently engage
in
cer-
tain conduct which they subjectively believe
to be
legally required
can
probably
be
considered
to
"consent"
to the
resultant rules
of
customary
international law.
In
fact,
as we
shall see,
the
consistency
of
customary
international
law
with
the
theory
of
consent depends crucially
on
what
is
meant
by
"consent"
and on
certain other
factors,
such
as the
meaning
given
to
"consistently,"
or the
number
of
subjects which must
be
found
to
"believe." Further,
the
idea
of
customary international
law can
also
be
argued
to be
consistent with natural
law
theories, particularly
if
prac-
tice
and
subjective belief
are
considered law-evidencing rather than law-
creating. More fundamentally, natural
law
theories might furnish
an
explanation
for why
states would believe certain practices
are
legally
obligatory where positivism might not. Thus customary international
law
mirrors
the
modern eclecticism
of
international legal
theory.3
In any
case,
the
idea that
binding
norms
of
international
law can be
derived
from
the
behaviour
and
beliefs
of
states
has
long been accepted
by
international legal
theorists4
as
well
as by
states themselves. Some
twentieth century theorists have questioned
the
continued importance
of
custom
as a
source
of
international
law
given
the
proliferation
of
multilateral codification
or
law-making treaties, which occupy much
of
the
"territory"
formerly
covered
by
custom. Some have wondered
if
this
tendency
to
codify
is a
natural
result
(and
indicator)
of
international
2
Caution
is in
order
so as not to
take this illustrative analogy
too
far.
The
reference
to
common
law as a
type
of
customary
law is not
meant
to
suggest that customary
international
law is a
form
of
international common law.
As we
have seen (above
Chapter
3
(C)(5)),
there
is no
concept
of
binding
judicial precedent
in
international law.
In
customary international law,
it is not the
consistent practice
of
judges that
is
legally
significant,
but
rather
the
consistent practice
of
states.
3 See
above Chapter
3
(B)(3).
4 See
above Chapter
3
(B)(l)
and
(2).
162
PUBLIC
INTERNATIONAL
LAW
law's evolution
from
its
"primitive" customary origins
to a
more delib-
erate,
thought-out system. Notwithstanding these musings, customary
international
law
continues today
to be
widely accepted, along with
treaties,
as one of the two
principal sources
of
international law. Article
38(1
)(b)
of the
gives
modern
expression
to
this acceptance
by
identifying "international custom,
as
evidence
of a
general practice accepted
as
law."
It
would
be
difficult
to
overstate
the
profoundly important role
played
by the
concept
of
customary international
law in the
interna-
tional legal system.
In
contrast
to
treaty law, customary international
law
is,
with rare exceptions
to be
noted
below,5
universally
binding
on
all
states.
It
thus constitutes
the
substratum
of
common legal rights
and
obligations
of the
entire community
of
states, upon which their more
particularized legal relationships (usually
in the
form
of
treaties)
are
built. What
is
more, customary international
law is an
enormously
powerful
normative concept
in
that
it can
have
the
effect,
under certain
circumstances,
of
binding states which have
not
actually consented
to
its
content
at
all.
It
thus challenges positivist interpretations
of the
the-
ory of
consent.
At the
same time,
it
receives universal endorsement
as a
valid
source
of
international law.
The
other striking implication
of
such
a
source
of law is
that
it is
forever
evolving under
the
influence
of the
actions
of its own
subjects.
In
other words,
the
legal significance
of a
state's behaviour
is not
lim-
ited
to its
consistency
or
inconsistency with
the
law.
Its
significance
can
extend,
in the
right circumstances,
to
influencing
the
content
of
the law
itself.
This can,
of
course, pose problems
for the
application
of
the law in
particular instances.
If the
content
of
customary interna-
tional
law is by
definition dynamic,
how can its
content
be
determined
or
applied with
any
precision
at any
given point
in
time? Should
a
state's behaviour which
is not in
conformity with past state practice
be
condemned
as
contrary
to
customary international law,
or
should
it
rather
be
considered evidence
of a new
customary rule?
The
require-
ments
for the
formation
and
determination
of
customary international
law
reviewed below provide partial answers
to
these
and
similar ques-
tions,
but the
fundamental
paradox persists
— a
system
of law
which
governs
the
behaviour
of its
subjects while
itself
being subject
to
modi-
fication
by
such behaviour.
See
below
Sections
(D), "Persistent
Objectors"
and
(E),
"Regional
or
Special
Customary
International
Law."
5
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