How Customary is Customary International Law?
How Customar y is Customar y International Law?
Emily Kadens 0
Ernest A. Young 0
0 Emily Kadens and Ernest A. Young, How Customary is Customary International Law?, 54 Wm. & Mary L. Rev. 885 (2013), https://scholarship.law.wm.edu/wmlr/vol54/iss3/7
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EMILY KADENS* & ERNEST A. YOUNG**
TABLE OF CONTENTS
* Professor of Law, Northwestern University School of Law. Professor Kadens would
like to thank the John W. Kluge Center at the Library of Congress for the time and
support to pursue this research.
** Alston & Bird Professor, Duke Law School. We are grateful to Michael Green and the
Institute of Bill of Rights Law for the opportunity to participate in the Symposium “Law
Without a Lawmaker” at William & Mary Law School on February 24-25, 2012.
INTRODUCTION
The ambiguity of the lawmaker has long been a central problem
in international law. Writing in the positivist tradition, H.L.A. Hart
famously doubted that international law is law at all because it
lacks not only a single sovereign lawmaker but also a system of
“secondary rules” for the making and alteration of legal norms.1
Treaties bind by consent, but only between the parties. Even when
large majorities of countries sign on to multilateral agreements, we
often lack any authoritative method for determining those
agreements’ meaning or guaranteeing consistent enforcement. In any
event, treaty law leaves large gaps,2 and often those gaps exist in
those areas with the most pressing need for law. In an earlier age,
international lawyers frequently turned to natural law to fill these
gaps,3 but a revival of the natural law tradition seems unlikely at a
time when countries with widely varying religious, philosophical,
and political traditions aspire to agree on one international law.4
Enter custom—the only form of law without a lawmaker still
recognized in our post-lapsarian world. At certain times and places
in world history, custom is thought to have given rise to a coherent
and effective set of legal norms “from the bottom up”—that is,
without the command of a single sovereign.5 If merchants operating
across state borders over time can produce a set of customary rules
to govern their transactions, even without formal consent or the
intervention of a sovereign authority,6 then perhaps independent
nations similarly can derive binding norms of conduct from their
own practices. Conventional wisdom in international law thus holds
that the international community has developed a set of definable
rules through custom that nations must accept as law.7 This wisdom
rests on extrapolation from the historical success of custom in
commercial law. On this view, customary international law derives
its appeal not only from a fear that it may be the only game in town
but also from a widely held sense that it is, well, customary.
We question that latter assumption in this Article by comparing
early theories of custom with the debates in which publicists engage
today. Article 38(
1
)(b) of the Statute of the International Court of
Justice asserts that custom, defined as “evidence of a general
practice accepted as law,” forms a fundamental part of international
law.8 This assumption about the role of custom has a well-known
history extending back to the writings of the Spanish theologian
Francisco Suárez (1548-1617), who equated the law of nations with
custom in his Treatise on Laws and God the Lawgiver of 1613.9 This
history, however, has a prehistory that modern scholars do not know
as well, and that prehistory sheds some interesting light on current
debates about the usefulness of the standard definition of custom.
The value of studying history lies not in any claim that
premodern jurists had better answers than do scholars today, but rather in
a historical perspective on the problem of how custom functions as
law. That problem, then as now, remains largely intractable. The
debates among jurists of the thirteenth and fourteenth centuries
mirror the debates in which their intellectual descendants engage
hundreds of years later. The story of custom, in both its past and
present manifestations, thus underscores contemporary doubts
about the usefulness of customary law on the international plane.
Part I of this Article surveys the historical development of
customary law. Part II ventures some suggestions as to what that history
can tell us about current debates over customary international law.
I. AN INTELLECTUAL GENEALOGY
Following the parameters laid down in Roman law,10 the medieval
jurists believed that custom consisted of acts, repeated with some
degree of frequency over some period of time, that the community
—or some part thereof—understood itself to be obligated to continue
performing due to its tacitus consensus, a phrase usually translated
as “tacit consent.”11 Scholars of customary international law today
begin, whether in support or opposition, from nearly identical
premises.12
Nearly, that is, but not quite identical, for modern publicists
generally use t (...truncated)