Table Of ContentThe Invention of Custom
THE HISTORY AND THEORY OF
INTERNATIONAL LAW
General Editors
NEHAL BHUTA
Chair in International Law, University of Edinburgh
ANTHONY PAGDEN
Distinguished Professor, University of California Los Angeles
BENJAMIN STRAUMANN
ERC Professor of History, University of Zurich
In the past few decades the understanding of the relationship between nations has undergone a
radical transformation. The role of the traditional nation-s tate is diminishing, along with many
of the traditional vocabularies which were once used to describe what has been called, ever since
Jeremy Bentham coined the phrase in 1780, ‘international law’. The older boundaries between states
are growing ever more fluid, new conceptions and new languages have emerged which are slowly
coming to replace the image of a world of sovereign independent nation states which has dominated
the study of international relations since the early 19th century. This redefinition of the international
arena demands a new understanding of classical and contemporary questions in international and
legal theory. It is the editors’ conviction that the best way to achieve this is by bridging the traditional
divide between international legal theory, intellectual history, and legal and political history. The aim
of the series, therefore, is to provide a forum for historical studies, from classical antiquity to the 21st
century, that are theoretically informed and for philosophical work that is historically conscious, in the
hope that a new vision of the rapidly evolving international world, its past and its possible future, may
emerge.
PREVIOUSLY PUBLISHED IN THIS SERIES
The Right of Sovereignty
Jean Bodin on the Sovereign State and the Law of Nations
Daniel Lee
Jews, Sovereignty, and International Law
Ideology and Ambivalence in Early Israeli Legal Diplomacy
Rotem Giladi
The Invention of Custom
Natural Law and the Law of Nations,
ca.1550– 1750
FRANCESCA IURLARO
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Series Editors’ Preface
The Law of Nations – the ius gentium – had originally been merely the law which
the Romans had applied to their – predominantly commercial – relations with non-
Romans. It took on a wholly new significance, however, after the ‘discovery’ of the
Americas, which had in effect brought into existence what the German jurist Carl
Schmitt in 1951 described as ‘the traditional Eurocentric order of international
law’. In this book Francesca Iurlaro offers a broad- ranging and powerfully compel-
ling new account of just how this new ‘order of international law’ transformed what
had once been a form of law based upon a voluntary agreement between peoples,
into one which was supposed to be binding on all peoples across the globe – and
might thus be imposed by one people upon another. She charts the evolving strat-
egies by which a succession of jurists, theologians, and humanists from Francisco
de Vitoria in the 16th century until Emer de Vattel in the eighteenth, sought to
create a ‘new law which was universally applicable to the global community (orbis),
regardless of the specific cultural and historical contexts of local political commu-
nities’. This tied the Law of Nations to the Law of Nature (the ius naturae) – the
Thomist and neo-Th omist elaboration of the claim that there existed in nature it-
self a single basic form of knowledge for all humankind, which was discoverable
through the use of human reason. The Law of Nature, however, was in effect a piece
of cognitive machinery capable only of generating a universal order of justice. The
jurists who contributed to the creation of Schmitt’s ‘traditional Eurocentric order
of international law’ required something more precise – and ultimately enforce-
able – something capable, in effect, of creating a true positive law. To do this they
turned to custom to provide the normative foundation for a universal legal code.
In so doing, however, they transformed what was understood to be ‘custom’ from
a collection of exemplary regulations – which inevitably varied greatly from one
people to another – into ‘an unwritten norm that the jurist could unravel from the
diverse manifestations of human history.’ Out of this emerged a new genre: the
‘Law of Nature and Nations’ which dominated the thinking about the relationship
between peoples and states from the mid sixteenth until the end of the eighteenth
centuries. Custom was now cast, not as the accumulated practices of individual
societies but as the collective expression of the consensus of all peoples (consensus
omnium gentium). It was, as Francesca Iurlaro explains, interpreted ‘as being both
temporally situated – an institution whose foundations resided in Roman law,
Christian religion [and] European classical antiquity – and universal at the same
time.’ Although there were recognized to exist customs that were restricted to in-
dividual communities, and which were, where possible, accepted as valid by the
vi Series Editors’ Preface
European colonizing powers, the kind of custom capable of sustaining an inter- na-
tional law could only, as Francesca Iurlaro explains, be arrived at through sustained
inquiries into a history which was believed to provide secure evidence of univer-
sality. ‘Authors of the natural law tradition’, as she puts it, ‘invented customary rules
of ius gentium precisely in an open dialogue with the past.’ The customs of the an-
cient – European – world, ‘constructed and fictionalized as universal’ – came to
stand in for those of the orbis terrarum in its entirety. Custom, it was believed was
ultimately ‘capable of transitioning the naturalness of reason into the historicity of
specific political and cultural context.’
For all that the creators of the Law of Nature and Nations struggled to find in
history and literature – rather than in anthropology – a universal customary law,
custom remained, of course, stubbornly specific to individual societies, and even if
a ‘consensus of all peoples’ were to exist it would, as the 16th- century Saxon jurist
Samuel Pufendorf complained, be impossible to find just what it was. Universal
consensus could only, that is, ever really be a legal fiction, a counterfactual, a device
as Francesca Iurlaro describes it, intended to ‘imagine concepts which are unavail-
able, or even impossible, in reality.’ What the Law of Nations had in fact become by
the time Pufendorf was writing was not so much the assembled wisdom offered by
the customary practices of the peoples of the whole world, so much as what Hugo
Grotius described as the record of ‘the continual experience and testimony of the
Sages of the Law’ – in other words, not so much a consensus of custom as what
Francesca Iurlaro calls a ‘mere agreement among arguments’. It also, of course,
meant that only those peoples who had recognized ‘sages of the law’ – and thus a
recognizable legal culture – could ever plausibly be part of the “Law of Nations”.
It was, as many have subsequently complained, but a short step from this to ar-
guing that the Law of Nations was in effect only the law of ‘civilized’ nations, or as
the English legal historian Robert Ward declared in 1795, that ‘what is commonly
called the Law of Nations . . . is not the Law of all Nations, but only of particular
classes of them; and thus there may be a different Law of Nations for different parts
of the globe.’ And if that were the case, then the entire universalizing purpose of
the project would seem to have collapsed altogether. As many more recent critics,
in particular those from the Global South, have protested, what the Law of Nature
and Nations in effect did was to divide the world not, as Ward had argued, into
many, but only into two: the ‘civilized’ nations of the globe who were bound by the
Law of Nature and Nations, and the non-c ivilized who, like pirates, would remain
the ‘perpetual enemies of mankind’ – until they were gathered into the folds of the
‘civilized’.
By the time Ward was writing, however, the direction of the argument, as
Francesca Iurlaro explains, had changed entirely. For the Prussian polymath
Christian Wolff – known to his contemporaries as ‘our German Newton,’ – and the
diplomat Emer de Vattel, the last and the most lastingly influential of the writers
in the tradition of the ‘Law of Nature and Nations’, custom could no longer be
Series Editors’ Preface vii
constructed, on the basis of supposedly universal history and literary tradition, by
‘the mass of jurists’ who, in Wolff’s view, only ever worked backward from ‘their
preconceived opinions’. What Vattel called the ‘customary law of nations’, had, in-
stead, if it were to possess any lasting authority, to be ‘founded on a tacit consent,
or, if you please, on a tacit convention of the nations that observe it towards each
other’. It had, that is, to be discoverable in some real historical past, and recognized
as local positive law.
The Invention of Custom offers an historical account based both on the wider
theoretical issues involved in the attempts to construct a persuasively universal
‘Law of Nature and Nations’ as well as of attempts by the very many jurists involved
to apply this to specific cases of inter-s tate relationships from how to deal with
cannibalism to such perennial questions as the rights of prisoners of war, and the
status of ambassadors. In the end as Francesca Iurlaro writes: ‘Looking at the past is
a value- making activity; it relies on a certain, culturally loaded, idea of temporality.’
This book offers what she describes as a ‘history of custom as an episode in the his-
tory of historiography’. But although modern international law may claim to have
entirely shed its ties to the natural law tradition, and thus to any reliance upon any
specific historical past, it is still the case, she argues, that it remains ‘to some extent,
a means of ordering the world through histories’. Until the story she has to tell in
this book has been fully understood, modern international lawyers run the risk of
being condemned, in her own words, to ‘replace old fabrications of the legal im-
agination with new founding fathers, new fictions, and new myths.’
Anthony Pagden
Acknowledgments
It is incredibly hard to do justice to all the people and institutions that supported
the publication of this book. It took way more than the proverbial village. However,
I will try, while I take full responsibility for any errors or mistakes it may contain.
This book is a revised version of my PhD dissertation, which I defended in
September 2018 at the European University Institute (EUI), under the supervi-
sion of professor Nehal Bhuta. Nehal Bhuta deserves a special place in this thankful
note. Over the past years, he has always supported and challenged me with his bril-
liant mind and enthusiasm, and always encouraged me to see the theoretical forest
whenever I was getting too lost in my textual trees. I am grateful that I had the
chance to meet him, and to have been exposed to his intellectual generosity.
The openness of the EUI academic environment made this journey even more
engaging. Thanks are due to all the people I met there, professors, fellow re-
searchers, and friends, who have supported me over these years in various and
often unconscious ways. Special thanks are due to the members of my PhD com-
mittee, Benedict Kingsbury, Martti Koskenniemi, and Ann Thomson, who offered
stimulating feedback, guidance, and support to help me turn this thesis into a book
for publication. To achieve this goal, I have benefited from the support of various
institutions which provided me with all the time, financial support, and intellec-
tual excitement I needed to finish it. I am grateful to Anne Peters and Armin von
Bogdandy for their hospitality at the Max Planck Institute for Comparative Public
Law and International Law (MPIL) in Heidelberg back in 2018, where I spent the
summer as a visiting scholar; and for welcoming me again in 2020 as an Alexander
von Humboldt Postdoctoral Fellow. Thanks are due to the Alexander von
Humboldt Stiftung for granting me such fellowship, time, and freedom to think,
and financial support to work with ease. I am immensely grateful to Benedict
Kingsbury, my supervisor at New York University School of Law, where I spent the
academic year 2019–2 0 as a Global Postdoctoral Fellow, as well as to the Hauser
Global Law School Program for sponsoring the fellowship; and to Marco Geuna
(Università degli Studi di Milano), with whom I had the privilege to work as a re-
search fellow in the first months of 2019.
Thanks are also due to Daniel Allemann, Stefano Bacin, Alessandro Barchiesi,
Erica Benner, Tommaso Braccini, Annabel Brett, Hans Blom, Maria Adele Carrai,
Paolo Carta, Gianmario Cattaneo, Bhupinder S Chimni, Janet Coleman, Emanuele
Conte, Jean D’Aspremont, Grainne de Burca, Wim Decock, Stefano di Bella, Paul
J du Plessis, Vanda Fiorillo, Alberto Frigo, Marco Geuna, Frank Grunert, Pablo
Kalmanovitz, Claus Kreß, Matthias Kumm, Randall Lesaffer, Karin Loevy, Ian
