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International law as a common language across
spheres of authority?
Chair for Public Law and Jurisprudence, Humboldt University, Unter den Linden 6, 10099 Berlin, Germany
Abstract: When actors express conﬂicting views about the validity or scope of norms
or rules in relation to other norms or rules in the international sphere, they often do so
in the language of international law. This contribution argues that international law’s
hermeneutic acts as a common language that cuts across spheres of authority and can
thus serve as a conﬂict management tool for interface conﬂicts. Often, this entails
resorting to an international court. While acknowledging that courts cannot provide
permanent solutions to the underlying political conﬂict, I submit that court pro-
ceedings are interesting objects of study that promote our understanding of how
international legal argument operates as a conﬂict management device. I distinguish
three dimensions of common legal form, using the well-known EC–Hormones case as
illustration: a procedural, argumentative, and substantive dimension. While previous
scholarship has often focused exclusively on the substantive dimension, I argue that
the other two dimensions are equally important. In concluding, I reﬂect on a possible
explanation as to why actors are disposed to resort to international legal argument
even if this is unlikely to result in a ﬁnal solution: there is a speciﬁc authority claim
attached to international law qua law.
Keywords: international law; international courts; legal authority; frag-
Under which conditions do interface conﬂicts become manifest, and, once
manifest, how are they managed, and what is the effect of such management
efforts? These are the main questions addressed in this Special Issue
(Introduction to this Special Issue). My contribution engages with the
question of how interface conﬂicts are managed.
More speciﬁcally, I
In line with the Special Issue’s understanding, I use the term ‘interface conﬂict’for situations
in which actors express conﬂicting views about the validity or scope of norms or rules in relation to
other norms or rules of which at least one is associated with an international authority.
explore which role international law plays in framing and managing
interface conﬂicts. I suggest that international law constitutes a common
hermeneutic, a common language that cuts across spheres of authority, and
that its cutting across spheres of authority enables it to function as a conﬂict
I proceed in three steps. In section II, I analyse how international law
relates to spheres of authority and argue that international law is mainly held
together by its systematicity on formal grounds, not by being geared towards
a substantive common social purpose. Rather, norms of international law
pursue a plethora of different purposes, ranging from free trade to human
rights, from environmental protection to civil aviation, from countering
terrorism to ensuring safe and fair labour conditions. International law’s
authority is thus varied and not the product of one speciﬁc legal domain.
Rather, law cuts across spheres of authority and constitutes a common
language, and therefore a common conﬂict management tool, that is valid
in principle for all sorts of interface conﬂicts.
In section III, I explore how international law’s role as a conﬂict manage-
ment tool is both reﬂected and enhanced by the multitude of international
judicial and quasi-judicial bodies which are designated to propose legal
solutions to disputes submitted to them. While such bodies are often (though
not always) anchored in one particular sphere of authority, the solutions
they propose radiate beyond the boundaries of each sphere. This is not to say
that legal solutions are superior to other types of solutions, or that managing
interface conﬂicts by resorting to international law as a form is particularly
desirable. I am not concerned here with the normative question of which
conﬂict management tool is the best. Rather, the argument is explanatory in
nature and seeks to establish how and why international law functions as a
conﬂict management tool across spheres of authorities. To this end, I
introduce three dimensions of common legal form: the procedural dimen-
sion, the argumentative dimension and the substantive, or ‘solutions’dimen-
sion. I use the interface conﬂict between the United States and Canada and
the European Union over hormone-treated beef to explore how these three
dimensions play out in litigation by revisiting the EC–Hormones case in
section IV and ﬁnd that while law certainly transforms and thus manages the
conﬂict, it does not always settle it deﬁnitively.
Rather, legal solutions proposed by a court or court-like institution, while
important for the course of interface conﬂict management as they will
inform further choices by actors, are seldom permanent and ﬁnal. I conclude
by reﬂecting upon why actors might nonetheless be disposed to dress an
interface conﬂict in legal terms. I suggest that on the one hand, the distinction
between law and non-law, while not always clear-cut, has as a consequence
that norms of international law put forward a claim to authority by virtue
International law as a common language across spheres of authority? 319
of their speciﬁc form as legal norms. On the other hand, turning an interface
conﬂict into a conﬂict of international law might detract from the underlying
conﬂict of competing social purposes. In this way, law qua form posits a
claim to universality, but one that is substantively empty.
II. How does international law relate to spheres of authority?
One central analytical concept of this Special Issue is the ‘sphere of author-
ity’. A sphere of authority is deﬁned as ‘a governance space with at least one
domestic or international authority, which is delimited by the involved
actors’perception of a common good or goal at a given level of governance’
(Introduction to this Special Issue).
Is international law a sphere of authority?
Given this deﬁnition, is international law a sphere of authority? At ﬁrst
glance, one might be inclined to think so. The statement ‘international law
possesses authority’is uncontroversial as long as one does not hold a purely
realist view claiming that international law is nothing but hubris, a collec-
tion of empty phrases exclusively masking power plays. It is not so clear,
however, whether the statement ‘international law is an authority’is equally
uncontroversial. An international authority, in the understanding of this
Special Issue, exists where an international institution’s decisions, judg-
ments and interpretations are recognised as binding or at least relevant by
a critical number of actors for their behaviour (see also Zürn 2018: Ch 3).
International law as such does not provide us with interpretations or
decisions –actors who refer to and apply international law do.
Of course, there are multiple actors in the international sphere –states,
non-governmental organisations, international bureaucracts, and perhaps
most importantly courts and court-like actors –who do exactly that: they
provide interpretations of norms and rules of international law and issue
decisions on its basis. But this means then that international law in and of
itself is not the site of authority, at least not in any comparable way to other
spheres of authority examined in this Special Issue, such as the sphere of free
trade, or the sphere of human rights, or of international security. There is no
goal pursued by international law as such; it is not geared towards a clearly
identiﬁable social purpose outside of the law. This is not a trait unique to
international law, but rather applies to law more broadly. The very function
of law might best be described as providing an institutional setting through
which attaining a given social purpose is subjected to a formalism that
requires actors to pause, to argue not with the moral valence of the social
purpose (or at least not exclusively), but through a speciﬁc form that enables
320 hannah birkenko
self-reﬂection (Möllers 2019). Thus, law does not have a ‘common goal’
outside of the law. If at all, law is an end in itself.
Norms of international law can thus wield authority,
law as such does not constitute a sphere of authority in and of itself, at least
not if we understand a sphere of authority as a governance space that is
delimited by actors’perception of a common good or goal. But what is it
then, and how does this thing called ‘international law’relate to spheres of
authority? We need to clarify how international law is positioned vis-à-vis
spheres of authority before we can examine in more detail how it might
function as a conﬂict management tool. This requires some reﬂection on
whether we can usefully speak of ‘international law’as a set of legal rules, or,
put more traditionally, whether or not international law constitutes a
International law as a system
Whether or not international law can be considered as a system has been
a perennial question of the discipline, and is often tacitly assumed.
Throughout all times, general international lawyers have not got tired of
asserting that international law could constitute a uniﬁed legal order
(cf. Simma and Pulkowski 2006), that it is a system (ILC 2006a: paragraph
To be sure, this was for the longest time an aspirational project
pursued by idealistic international lawyers (von Bernstorff 2019). Hans
Kelsen acknowledged that international law in the 1930s had been but a
‘primitive law’, even if he considered this to be a transitory stage and was
convinced that it might be assumed that ‘the technical development of interna-
tional law is progressing on the same path as that already taken by the devel-
opment of the legal orders of the States’–he saw international courts as the ﬁrst
step towards centralising international legal institutions (Kelsen 1941:97).
Famously, and in contrast to Kelsen’s optimistic outlook, HLA Hart
argued 20 years later that international law was precisely not a system
I will return to this thought in section V.
I am not interested here in an essentialist view of international law, nor do I believe that it is
necessary to pronounce on the ontological status of (international) law or of other questions
related to well-rehearsed ‘nature of law’debates (see for a similar point Hunt 1992: 5). My aim
here is more modest: I am trying to identify whether rules that we commonly refer to as ‘rules of
international law’share a common characteristic so that we can usefully talk of ‘international law’
as a set of rules.
Of course, there is some variety as to what precisely systematicity means. Pulkowski (2014:
204–34) has observed that ‘unity is a matter of degrees’and convincingly shows that there are
substantial differences between unity à la Kelsen, in which two contradictory, but equally valid
norms are inconceivable, and the idea of systematicity à la ILC Study Group and Martti
Koskenniemi, with a ‘highly relativized notion of legal unity’(at 223).
International law as a common language across spheres of authority? 321
(Hart 1961: Ch 10). Rather, Hart found, international law was a set of
primary rules, but lacked any secondary rules (of recognition, of change and
of adjudication). While individual rules of international law were binding –
rules of international law were clearly rules of law –Hart did not consider
the ensemble of existing rules to form a legal system. Rather, his vision of
international law was one of individual rules regulating single instances, but
with many gaps in between and many situations in which no applicable legal
rule existed. Hart’s view, articulated over half a century ago, has been
criticised vehemently since, both on grounds of changed empirical circum-
stances one ﬁnds today (Payandeh 2010) and on grounds of Hart’s own
inconsistencies (Murphy 2017). But engaging with his assertion that inter-
national law is not a system, and recent criticism of this position, helps
sharpen the contours of what is understood here as ‘international law’and to
position it in relation to one of this Special Issue’s main analytical entities,
namely spheres of authority.
Recently, Liam Murphy (2017: 207–13) has questioned Hart’sﬁnding
that international law does not know a rule of recognition. As mentioned,
Hart insists that single rules of international law can be individually legally
binding, i.e. valid, and that this does not require a rule of recognition. What
changes with a basic rule of recognition is that law becomes predictable: ‘in a
system with a basic rule of recognition we can say before a rule is actually
made, that it will be valid if it conforms to the requirements of the rule of
recognition’. Such a requirement, Hart posits, would be fulﬁlled if there was
general acceptance that e.g. multilateral treaties could bind states that are
not parties to the treaty (Hart 1961: 235). Against this assessment, Murphy
(2017: 210–11) argues that substantive criteria exist for assessing whether a
rule is a rule of international law.
These criteria are provided by what is
traditionally known as ‘sources theory’. Sources theory, concerned not only
with how international law is made, but also, more importantly for our
purposes here, with how it is identiﬁed, how to ‘speak the language of the
sources of international law’(Besson and D’Aspremont 2017: 7), provides a
framework within which any claim to legality must be made. While sources
theory is far from being unequivocal or undisputed, there is a general
consensus that international treaties, international custom and general
principles can be discerned as accepted sources of international law, and
that thus, some form of rule of recognition exists in the form of sources
theory (Besson 2010: 163–85).
That states may sometimes not accept the substantive content of individ-
ual rules of international law –i.e. by not ratifying a speciﬁc human rights
Murphy makes his argument exclusively with regard to customary international law, but
the point is more general.
322 hannah birkenko
treaty or by persistently objecting to the binding force of customary inter-
national law –means that we cannot know ex ante and in concreto upon
which individual subjects of international law a rule of international law will
exert binding force (Hurd 2015: 376–81). But it is in principle possible to
know, ex ante, under which conditions a rule will be binding. There is a
categorical difference between abstractly accepting the existence of interna-
tional law as such, and accepting the substantive content of an individual
rule of international law.
International law’s institutional challenge
Murphy (2017: 212) further notes that the ILC and other defenders of the
systematicity of international law might not necessarily use the term ‘system’
in a Hartian sense. While Hart requires the union of primary and secondary
rules for a collection of legal rules to be called a ‘legal system’, Murphy
suggests that the term ‘system’with regard to international law might
perhaps be better understood in terms of how the rules of international
law relate to each other, as a system of ‘interlocking norms’.
law and domestic law differ in their institutional structures in obvious ways
(Murphy 2017: 213). The most obvious such difference, investigated at
length by Collins (2016), is international law’s decentralised institutional
nature, i.e. the absence of a central or uniﬁed authority similar to the state in
domestic law that is exclusively in charge of interpreting and administering
One terminological note of caution is in order. When international law-
yers talk about the ‘institutional’dimension of (international) law, they are
usually referring to the kinds of organisational entities which administer the
law and how these are arranged in relation to one another. The institutio-
nalisation of international law is typically associated with the emergence of a
range of organisations that are in charge of administering, interpreting and
further developing rules of international law (see e.g. Collins 2016: Ch 8).
International relations scholarship in turn standardly deﬁnes the term ‘insti-
tution’as ‘persistent and connected sets of rules (formal and informal) that
This terminology is based on Raz’distinction between an ‘institutionalized’(domestic legal)
system versus a system of ‘interlocking norms’(Murphy 2017: 213).
Of course, one might question whether this image of the state as the exclusive authority in
determining the existence and content of one single form of law is accurate to begin with. For a
critique of this approach inspired by Foucault’s study of the state whilst criticising Foucault’s
‘expulsion’of the law from his theory see Hunt (1992: 9). A similar point, albeit somewhat more
enigmatically, is made by Cover (1983). Be that as it may, the contemporary constitutional state
clearly exercises de facto the most substantial amount of interpretive authority when it comes to
domestic law. Thus, international law arguably suffers from a bigger indeterminacy problem in
practice than does domestic law (Collins 2016: 7; Besson 2010: 178; Koskenniemi 1989).
International law as a common language across spheres of authority? 323
prescribe behavioral roles, constrain activity, and shape expectations’
(Keohane 1989: 3) and differentiates between international organisations,
understood as entities, and international institutions, understood as rules
(see e.g. Martin and Simmons 2013: 326). Thus, legalisation is often char-
acterised as a particular form of institutionalisation (Abbott et al. 2000:
401). These two viewpoints are not incompatible. But there is a danger of
confusion. Very often, when international relations scholarship focuses on
institutions that are not law, these institutions risk to be easily conﬂated with
international organisations that embody them. And because international
law scholarship’s main focal point is a particular rule-set, namely law as
opposed to other, non-legal rules, it sees no need to explicate its narrower
understanding of the term ‘institutional’.
This terminological confusion contains a ﬁrst hint towards understanding
better how international law is positioned vis-à-vis other rule-sets in the
international sphere. While it is true that a legal rule is a particular type of
rule, and that thus, we can usefully speak of ‘legalisation’as an instance of
institutionalisation in certain contexts, this obscures at the same time the
particularities law possesses vis-à-vis other forms of institutionalisation.
Law might be an institution in the sense of international relations, but the
way in which legal rules are related to one another is different from the way
in which rules within other institutions connect to each other: legal rules are
mainly held together by their systematicity, i.e. individual rules can in
principle be traced back to some form of acknowledged pedigree, to a
recognised source. Thus, formal law cuts across institutions that are each
held together by a common substantive purpose, or function. Put in terms of
this Special Issue: international law is not embodied by one authority, or
several authorities that are connected by a common substantive purpose.
Rather, international law cuts across spheres of authority. Simultaneously,
most spheres of authority studied in this Special Issue have a plethora of
different types of rules and norms, not all of which are claimed to be rules of
international law. The rules of international law within a sphere of authority
will standardly be less than the total number of rules simpliciter within that
The institutional (or rather: organisational) challenge of international law
consists in the fact that the entities administering international law are
organised in a decentralised fashion. Because these entities are often and
inadvertently compared with the state and its centralised organisation,
expectations that people have in international law are perpetually frus-
trated, because they rest on assumptions of organisational administration
of international law that are simply not accurate as a matter of fact (Collins
2016). For example, Hart’s requirement that international treaties should
bind non-parties sits fundamentally at odds with the decentralised nature of
324 hannah birkenko
international law, which speciﬁcally and inherently provides that many rules
of international law will not be applicable to all subjects of international law
equally (Hurd 2015: 389–90). Not each individual rule of international law
is universally applicable in concreto, but its claim to be law is of a universal
nature. Because of this inherent feature of international law, its status as a
legal order has perhaps always been more volatile than that of domestic law.
Even if domestic law also knows rules that are not applicable to every single
one of its subjects (e.g. rules that apply to homeowners, but not to people
who rent; rules that apply to adults, but not to children; rules that apply only
to members of a certain profession), this is different from the case of
international law, in which the subjects themselves are in many cases capable
of determining whether or not a rule applies to them.
Domestic law makes
its distinctions based on differentiations external to the subjects in question.
In international law, in turn, the excluded and included subjects belong to
exactly the same category, even if not all rules apply to all subjects.
If we look at fragmentation from this perspective, it can be viewed
ultimately as a form of partly uncoordinated differentiation which also
exists in domestic legal systems (Möllers 2017)–but whereas in the domestic
legal system, such uncoordinated differentiation is the exception, at the
international level, it is the rule. This is not necessarily a bad thing: in fact,
it might be an advantage, as it permits more actors to contend with one
another, rather than hierarchically imposing a solution.
III. International law as a conﬂict management mechanism
In fact, despite international law’s inherently decentralised institutional
nature, recent scholarship has found that the fragmentation scare has been
largely unfounded and that actors across different institutions are more
cooperative than confrontative (e.g. Peters 2017; Boisson de Chazournes
2017; Andenas and Bjorge 2015). This contribution looks at the way in
which international law can be used as a tool to frame interface conﬂicts, in
particular those conﬂicts that are at their core about diverging social pur-
poses in the global sphere. I submit that legal arguments and legal language,
as used primarily in court proceedings, constitute a common hermeneutic
This is not the case for peremptory norms of international law (ius cogens), and arguably not
the case either for newly emerging subjects (states) that are instantly subjected to international
customary law. Perhaps the difference between domestic and international law is best thought of
as a reversed rule–exception relationship: in international law, subjects are in principle capable of
determining the applicability of a rule, whereas in domestic law, a state’s subjects are in principle
subjected to that state’s law, with exceptions in both cases.
International law as a common language across spheres of authority? 325
that acts as a tool to both frame and propose (temporary!) solutions to
Legal argument as regulated interface conﬂict management
The framework proposed in this Special Issue distinguishes three types of
cooperative conﬂict management (Introduction to this Special Issue): it is
constitutionalised where norms of meta-governance are applied through
institutionalised procedures to authoritatively solve interface conﬂicts; it is
norm-based where the conﬂict is solved with reference to third norms,
i.e. norms different from the ones that are in conﬂict with one another;
and it is decentralised (yet cooperative) where the parties show a willingness
for mutual accomodation and political compromise, but do not resort to
third norms or delegate solution of the conﬂict to a third party (for case
studies of such decentralised conﬂict management see Krisch et al. in this
Conﬂict management through international legal mechanisms belongs to
the category of norm-based conﬂict management, i.e. conﬂict management
with reference to third norms.
Norm conﬂicts in international law are often
solved through resorting to norms of interpretation, which are different
from the norms in conﬂict with one another and thus third norms. Consider
for example the conﬂict between the obligation to prosecute serious human
rights violations on the one hand and the rules of immunity from jurisdiction
for both public ofﬁcials as well as states, which pre-empt prosecutions of
such cases, on the other hand (ECtHR 2001; ICJ 2002; ICJ 2012; ECtHR
International courts that were faced with this conﬂict applied both
procedural norms as well as norms of interpretation in such a way that one
commentator opined that ‘any apparent conﬂict’had been ‘removed’
through the application of international law (Greenwood 2015: 46).
It should not be surprising that Greenwood considers international courts
to be the main actors in ‘removing’–i.e. managing, in terms of this Special
Issue –a conﬂict between norms. With an increasing number of international
Of course, constitutionalists would rather submit that international law, by favouring
constitutional principles, most importantly human rights, provides authoritative solutions to
interface conﬂicts, or at least that this ought to be so. For an argument in favour of a constitu-
tionalist approach in international law see Peters (2009), Kleinlein (2012a); for an argument that
constitutionalism, while not fully realised, might be an appropriate response to fragmentation and
bears great potential, see Paulus (2009).
Note that the quoted cases all involved the above-mentioned conﬂicting norms, but the
procedural contexts and actors putting forward claims differed (e.g. individuals claiming human
rights violations at the ECtHR, but states claiming immunity at the ICJ).
326 hannah birkenko
courts and tribunals as well as quasi-judicial bodies,
actors who claim for
norms to be in conﬂict often delegate their application and interpretation to
such a third party. While third parties can come from within an authority,
they are characterised by a certain amount of independence, and thus
constitute authorities in their own right.
The above example also shows that more than one court or court-like
institution might be competent to address a given interface conﬂict. This is
common for many interface conﬂicts. Consider for example the conﬂict
between the sphere of international security and the sphere of international
human rights, manifested as a conﬂict between the obligation to freeze the
bank accounts of individuals on the Security Council’s sanctions lists with-
out providing information about the listing and the obligation to ensure that
such individuals be properly informed of the grounds for their inclusion on
such lists, so as to be able to seek judicial review. While this interface conﬂict
is probably best-known as the ‘Kadi’saga at the European Court of Justice
(ECJ 2008,2013), it was also managed at the European Court of Human
Rights, where another listed individual, Youssef Moustafa Nada, chal-
lenged his listing ﬁrst in Swiss domestic courts and subsequently at the
European Court of Human Rights (ECtHR 2012; for an overview of both
the Kadi and Nada cases see De Wet 2013).
Lastly, the second example also shows that the actors who maintain
positional differences are different from the authorities embodying the
respective norm(s). In Kadi, the norms in question were embodied by the
UN Security Council on the one hand and the EU on the other hand, whereas
the actors with opposing views in front of the European Court of Justice
were the claimant, Yassin Abdullah Kadi, and the EU organs responsible for
imposing the freeze, i.e. the Commission and the Council. In addition, while
it was these actors who opposed each other in the court proceedings, they
were each part of a broader actor coalition (cf. Introduction to this Special
The limits of focusing on courts
The Kadi saga illustrates that court proceedings will often capture only a
fraction of a larger interface conﬂict. The focus on courts thus warrants
explanation. Courts are neither unique sites in which interface conﬂicts are
successfully handled, nor are they necessarily better positioned than other
actors in handling them. Framing interface conﬂicts through international
There is some disagreement as to how to precisely deﬁne international adjudicative bodies,
especially on whether it needs to be a permanent institution (which would rule out arbitration,
arguably a big part of the current international adjudicatory function) and whether all of its
decisions needto be legally bindingat least inte r partes,cf.Alter(2014): 70ff; Romano et al.(2013).
International law as a common language across spheres of authority? 327
law is only one possible way of interface conﬂict management, and it
happens not only within courtrooms. In fact, I agree that courts play only
a limited role in resolving interface conﬂicts (Dunoff 2012: 156). Despite
these caveats, I believe that scrutinising the way in which interface conﬂicts
are handled when submitted to courts is instructive if we want to understand
how international law functions.
There is a simple, but powerful reason for this: courts and court-like
institutions are required to use a particular type of rules when addressing
interface conﬂicts –legal rules. This is also true when the adjudicating
institution is part of one sphere of authority, e.g. the European Court of
Human Rights as an authority in the sphere of international human rights or
the WTO Appellate Body within the sphere of free trade. The actors involved
will use rules of international law to frame the interface conﬂict before courts
and court-like institutions, and these third-party actors will use rules of
international law to bring about a legal solution to the dispute at hand.
This does not mean that courts, especially those that are rooted exclu-
sively within a given sphere of authority, do not discharge functions other
than dispute settlement, law-interpretation and law-application, e.g. the
creation of unity within an organisational entity (Shany 2012:19–20), or
that a court’s hermeneutic does not entail essentially political considerations
(Howse 2011). But as Rosalyn Higgins (2006: 7) has emphasised, interna-
tional law continues to be an important point of reference for all interna-
tional courts. If we want to understand better what role international law
can possibly play in managing interface conﬂicts, then we need to ﬁrst
understand those cases that are squarely recognised as being legal. Studying
the legal forms deployed in international courts might not teach us much
about how whole regimes impact on and interact with each other (Dunoff
2012: 156–73). But it can illuminate the speciﬁcity of legal conﬂict manage-
ment vis-à-vis other forms of conﬂict management.
Three dimensions of common legal form
With this caveat in mind, I propose a systematisation of how legal argument
alters the way in which interface conﬂicts are framed. Three dimensions of
commonality in legal form can be usefully distinguished: the procedural
dimension, the argumentative dimension and the substantive, or ‘solution’,
dimension. This is an attempt at ordering the different types of legal form
that are standardly invoked in front of international tribunals.
Procedurally, actors will be constrained through legal rules as to which
conﬂicts they can submit to third-party actors. Not all actors are subject to
the jurisdiction of all courts or court-like institutions –the court needs to
establish its jurisdiction ﬁrst (ratione personae,materiae,temporis,loci). In
328 hannah birkenko
many cases, particular actors will be altogether unable to seize third-party
actors (e.g. individuals only have limited access to international jurisdic-
tions, and non-governmental organisations are generally excluded from
activating proceedings). Sometimes, other conﬂict management steps need
to have been undertaken (e.g. exhaustion of local remedies, or mediation or
conciliation procedures); often, there is only a particular set of substantive
rules that can be invoked. Where a situation is under consideration in one
judicial forum, it might be banned from submission in another forum (lis
pendens, for examples see Boisson de Chazournes 2017:46–9). The rules
regulating under which conditions a court can adjudicate a case or not –the
rules of jurisdiction and admissibility –are thus of primordial importance
and can enable courts to avoid pronouncing on the substance of conﬂicting
legal regimes. One such example is the Southern Blueﬁn Tuna arbitration, in
which an arbitral tribunal established under the UN Convention on the Law
of the Sea avoided ruling on whether the Convention substantively prevailed
over a trilateral ﬁsheries agreement between the litigating parties by pro-
nouncing that it did not have jurisdiction over the case (Arbitral Tribunal
2000). In addition, the procedural dimension also, and crucially, includes
rules on how the third-party actor will determine the underlying facts and
how they will be evaluated. This is often framed through rules of burden of
proof and evidentiary standards as well as the standard of review applied by
the respective third-party actor. All of these procedural rules –or third
norms, in the language of this Special Issue –will play a role in how an
interface conﬂict is managed.
At the argumentative level, only legal arguments will be accepted in front
of courts. This is one of the speciﬁcities of courts vis-à-vis executive agencies
and the legislature, and, of course, this is inextricably linked with the
procedural aspect (Möllers 2013: 92). This means that in order to justify
one’s behaviour or claim, the actor cannot exclusively refer to a norm, but
must at least implicitly (and better yet: explicitly) suggest that the invoked
norm fulﬁls speciﬁc requirements of pedigree. Put differently, an actor
invoking a norm as a norm of international law must either rely on such
attributes that are generally accepted as sources of international law
(e.g. that it ﬁgures in an international treaty), or must make an effort to
justify why a norm should be recognised as a legally binding norm. This has
consequences for the kinds of interface conﬂicts that are likely to be chan-
nelled through court proceedings: it only makes sense to seize a court or
court-like institution if the actor who wants to prevail can make at least a
plausible claim that there exists a legal norm. In addition, this claim must be
such that ideally, the opponent cannot make a plausible claim to legality as
well. It is a common strategy to argue that the norm the opponent relies upon
is not, or not yet, a norm of international law. For example, the United States
International law as a common language across spheres of authority? 329
argued in the EC–Hormones case, examined more fully below, that the
precautionary principle was an ‘approach’and not a norm of customary
international law, as claimed by the European Communities (WTO 1998:
paragraph 43). A similarly effective strategy, which leads back to the
procedural dimension, is to argue that the seized court does not have
jurisdiction over the norm that the opponent relies upon, even if the norm
is a legal norm.
Lastly, the conﬂict management devices that courts and court-like insti-
tutions choose to make explicit are again exclusively legal rules. Legal rules
come into play at two levels in resolving interface conﬂicts. The ﬁrst level
might be called ‘legal norm conﬂict resolution’proper: Where an interface
conﬂict has been framed as a conﬂict between two substantive norms of
international law, norm-conﬂict resolution rules come into play. These
include the rules of lex specialis,lex posterior and lex superior (ILC
2006b), but also conﬂict of laws approaches (Michaels and Pauwelyn
2012) as well as rules of justiﬁcation, excuses and the principle of propor-
tionality (Jeutner 2017: Part II). Take for example the Kadi litigation in the
Court of First Instance: here, the Court had resolved the conﬂict between
imposing the sanctions without informing the listed individual and the duty
to inform the individual and ensure a right of judicial review of the listing
decision through the application of Article 103 of the UN Charter, an
explicit precedence rule. The Kadi litigation shows, however, that a conﬂict
can also be solved without being explicitly framed as a conﬂict between two
legal rules. The European Court of Justice ruled exclusively on the basis of
European law, thus avoiding explicitly pronouncing on the conﬂicting rules.
This is not a singular instance. Often, international norms are vague and
cannot unequivocally be constructed as conﬂicting. Instead, they are in need
of interpretation (Jeutner 2017:22–7). This is where rules of interpretation
come in –rules that are in turn again rules of international law.
Pulkowski (2014: Ch 6) has suggested that some basic concepts of
international law (sovereignty, the right to have human rights, the Vienna
Convention on the Law of Treaties and the UN Charter) ought to be
viewed as ‘constitutive rules’that enable discourse between different legal
bodies, and thus lead to ‘communicative compatibility’.These‘discourse
rules of international law’(Pulkowski 2014: 238) correspond largely to the
rules mentioned in the third, ‘solution’, dimension above. While I do
consider these substantive rules to be important when courts are called
upon to provide a solution, I believe that a broader notion of legal conﬂict
resolution that also encompasses the procedural and formal legality
One important rule in this regard is art 31(3)(c) of the Vienna Convention on the Law of
Treaties. On its potential, see e.g. ILC (2006b: 206–43).
330 hannah birkenko
dimensions, as outlined above, captures more fully the elements of the
communicative compatibility that is characteristic for the thing that we call
IV. How does an interface conﬂict transform through litigation?
Revisiting the WTO’sEC–Hormones case
In order to illustrate how an interface conﬂict gets transformed and thus
managed through the involvement of a third-party actor, I revisit the World
Trade Organization’s Appellate Body (WTO AB) Report in one of its
landmark cases: the EC–Hormones dispute, the ﬁrst case in which the
WTO AB had to reconcile the free trade paradigm that had resulted from
the Uruguay round with health and environmental protection consider-
ations. The choice of the case might be surprising at ﬁrst glance: EC–
Hormones is primarily known as ‘the most important dispute decided under
the Agreement on the Application of Sanitary and Phytosanitary Measures
(SPS Agreement)’(Koebele 2007),
not necessarily as an interface conﬂict.
In addition, it was one of the ﬁrst cases at the WTO AB, and, issued in 1998,
appears to be rather dated. I hold that the case is nonetheless instructive if we
want to understand not only how legal argument alters and manages an
interface conﬂict, but also in order to explore the limits of focusing on court
decisions and conﬂict management through international law.
The EC–Hormones litigation as an interface conﬂict
In EC–Hormones, as will be examined in more depth below, the WTO AB
issued its decision on the basis of WTO law alone and did not make any
ﬁnding as to the alleged norm conﬂict between WTO law and general
international law. But this does not mean that the underlying dispute could
not have been reasonably conceived of as a norm conﬂict, or that no
interface conﬂict existed. The US had brought the case to the WTO Dispute
Settlement Mechanism in 1996, claiming that the European Communities’
import ban on meat was violating several provisions of the GATT and other
The European Communities countered that the import
The SPS Agreement is the WTO agreement regulating how WTO members can apply food
safety and animal and plant health measures.
Speciﬁcally, the US argued that the measure constituted a violation of art III GATT 1994/47
(national treatment rule), art XI GATT (prohibiting import restrictions), arts 2, 3, 5 SPS Agree-
ment (which specify exceptions to GATT provisions, cf. also art XX(b) GATT), art 2 TBT
Agreement (national treatment rule) and art 4 Agriculture Agreement (no import restrictions).
Cf. WTO (1996). Canada followed suit a few months after, after having initially joined the US
case as a third party.
International law as a common language across spheres of authority? 331
ban was justiﬁed under the precautionary principle as a principle of inter-
national environmental law. In other words, the European Communities
argued the existence of a norm conﬂict: they suggested that the prohibition
to impose import restrictions, stemming from the obligation to ensure free
trade, was in conﬂict with the obligation to prohibit the import of potentially
harmful food products, stemming from the obligation to protect the envi-
ronment and health.
The EC–Hormones litigation is thus a prime example of what, in this
Special Issue, is conceptualised as an interface conﬂict across spheres of
authority: we have actors who explicitly disagree about how different norms
and rules relate to one another, with a set of the norms in question associated
with the World Trade Organization as an international authority. As such,
the EC–Hormones case has also been important for the fragmentation
debate in international law. The International Law Commission’s Study
Group on fragmentation considered EC–Hormones to be representative of
fragmentation as the result of ‘different special laws’, namely international
trade law on the one hand and international environmental law on the other
hand, and cautioned that the WTO AB’s approach ‘suggests that “environ-
mental law”and “trade law”might be governed by different principles’(ILC
2006b: paragraph 55, emphasis added). These ‘principles’are roughly
equivalent to what this Special Issue conceptualises as differing social
purposes of different spheres of authority.
Against this backdrop, it is perhaps not surprising that the 1998 WTO AB
Report did not settle the conﬂict deﬁnitively. Rather, it is only one singular
instance of a protracted interface conﬂict between the United States and
Canada on the one hand and the European Communities on the other hand,
lasting over two decades. Following the 1998 Appellate Body report, which
found that the European Communities’beef import ban was violating WTO
law, the European Communities amended its internal EC law to allow for
the administration of certain growth hormones. The United States and
Canada judged this insufﬁcient and suspended concessions granted to the
European Communities on the grounds of non-compliance. The European
Communities, however, considered that they had in fact removed the mea-
sures found to be inconsistent with WTO law and thus complied with the
Appellate Body Report. Now, the EC requested consultations, complaining
that the continued suspensions of concessions were in turn violating WTO
law (WTO 2004a; WTO 2004b). Both disputes were ultimately managed
through mutually agreed solutions, in the case of the conﬂict between the EC
and Canada through the negotiation of the Comprehensive Economic and
Trade Agreement (CETA; WTO 2017) and in the case of the conﬂict
between the EC and the US through a Memorandum of Understanding
332 hannah birkenko
(WTO 2014). From this perspective, the interface conﬂict is much more
recent than the date of the Appellate Body report might suggest.
Lastly, while the EC–Hormones litigation concerned exclusively the
import of meat where animals had been treated with certain growth hor-
mones, additional cases at the WTO have addressed questions of genetically
modiﬁed food and agricultural technology, a question that ultimately
remained unresolved politically, despite several attempts at ﬁnding a coop-
erative solution (WTO 2006; Pollack and Shaffer 2009: Ch 5). The EC–
Hormones case is thus part of a larger complex of related transatlantic
confrontations over genetically modiﬁed products and other forms of bio-
technical engineering. At the bottom lies a fundamental disagreement as to
whether food production ought to be subject to various forms of bioengi-
neering, so as to improve the products at hand and enhance trade in them, or
whether such treatment ought to be subject to a precautionary approach in
order to guarantee maximum environmental and health protection –or, put
in terms of this Special Issue, an interface conﬂict between spheres of
authority. In the remainder of this section, I shall address the three dimen-
sions of common legal form as they appear in the EC–Hormones Appellate
Body report, all the while keeping in mind that this case only represents one
particular instance of conﬂict management in a larger and much more
protracted interface conﬂict (see Introduction to this Special Issue:
Figure 2, for an analytical model of the interface conﬂict framework).
Proceduralising interface conﬂicts
As mentioned before, the procedural dimension is concerned with framing
the conﬂict in legal terms. This includes, crucially, rules about how the court
or court-like institution will establish the facts upon which it will base its
judgment. In the EC–Hormones appeal, several points on the evidentiary
standards and the underlying facts were raised. The European Communities
argued inter alia that the Panel had erroneously put the onus of burden of
proof on the EC, despite its status as responding party,
that the standard of
review for the Panel ought to have been whether the measure was reason-
able, and not whether it was conforming to an assessment of the scientiﬁc
evidence as carried out by the Panel, and lastly, that the way in which the
Panel had assessed the facts and evidence presented to it had not been
adequate, and that it ought to have established an expert review group
(WTO 1998: paragraphs 9–18, 37). Here, we can observe that the under-
lying interface conﬂict is not really visible –in fact, the main consequence of
Most legal systems know the principle by which the party putting forward a claim in
adversary proceedings needs to provide the necessary proof to support its argument.
International law as a common language across spheres of authority? 333
proceduralisation is that the interface conﬂict is precisely not being framed
as an interface conﬂict. Thus, in response to the EC’s claim that the Panel
ought to have established an expert group, the US not only argued that no
such obligation existed under the Dispute Settlement Understanding, but
additionally, and primarily, claimed that the EC would have needed to make
that claim earlier in the proceedings. Because it had not raised this proce-
dural grief during the Panel proceedings, the US argued that it was now
precluded from doing so (WTO 1998: paragraph 54). This is a good
example of how proceduralising an interface conﬂict radically alters the
way in which the conﬂict is framed: no matter of substance is raised here
Legal argument as a form: The importance of formal sources
The EC–Hormones case is perhaps best-known amongst international law-
yers for its (non-)treatment of whether the precautionary principle is a rule of
customary international law and if so, how it would relate to WTO norms.
Famously, the Appellate Body did not decide this question, but rather argued
that it was ‘unnecessary, and probably imprudent, for the Appellate Body in
this appeal to take a position on this important, but abstract, question’
(WTO 1998: paragraph 123). However, the very fact that the EC had
argued that the precautionary principle formed part of customary interna-
tional law, or constituted a general principle of law, evidences that the EC
needed to claim that the precautionary principle was indeed part of formal
international law. It would not have been sufﬁcient to claim that the
precautionary approach was, as a matter of fact, superior to the approach
taken on growth hormones by the US and Canadian authorities. Appealing
to the substantive function of the rule is not enough. Rather, for the
precautionary principle to be applicable to the situation at hand, the EC
had to argue that it could be traced to a speciﬁc source, or sources, of
international law (WTO 1998: paragraph 16). In turn, and accordingly,
both the US and Canada tried to fend off that claim by denying that the
precautionary principle was a rule of customary international law or a
general principle in the sense of Article 38(1)(c) ICJ Statute. Instead, they
suggested that something called a ‘precautionary approach’might exist, but
that such an approach was legally irrelevant (WTO 1998: paragraphs
43, 60). Both parties reiterated these stances a few years later, in the Biotech
litigation addressing the same underlying interface conﬂict between the
obligation to import bioengineered products and the precautionary princi-
ple prohibiting import of those products (WTO 2006; for comment see
Pollack and Shaffer 2009: Ch 5), with the panel concluding again that it did
334 hannah birkenko
not have to pronounce on whether the precautionary principle was a legal
norm (WTO 2006: 341, paragraph 7.89).
The ‘solutions’level: interpretation rather than conﬂict rules
Since the Appellate Body made no ﬁnding on the precautionary principle,
but considered it to be reﬂected in several provisions of the SPS Agreement,
the appeal mainly turned around the Panel’s interpretation of these pro-
What is important for the purposes of this article is that the
Appellate Body did not apply any ‘proper’conﬂict resolution norms: it
did not frame the underlying interface conﬂict between the social purposes
of free trade and environmental and health protection as a conﬂict between
two legal norms. Rather, all substantive issues were issues of interpretation
of various SPS Agreement provisions.
Again, the fact that the Appellate
Body in EC–Hormones, and, subsequently, the panel in Biotech, did not
make a ﬁnding as to the legal status of the precautionary principle and opted
to resolve the case exclusively through the SPS Agreement does not mean
that there was no norm conﬂict to begin with. Indeed, it has been argued that
from a legal-doctrinal point of view, it would have been more appropriate
for the WTO AB to pronounce on the status of the precautionary principle,
and, if it had found the precautionary principle to constitute a rule of
customary international law, to resolve the conﬂict between the two norms
through applying the lex posterior and lex specialis rules, respectively
(Pauwelyn 2003: 482).
This underlines that interpretation of legal rules by courts is an important
way in which interface conﬂicts are managed through international legal
rules –and that such conﬂict management can also entail avoidance of the
conﬂict. In the EC–Hormones case, the Appellate Body rephrased the norm
conﬂict that it had been presented with in terms of the WTO’s Covered
Agreements and could thus address it through exclusively applying WTO
law. A characteristic of courts and court-like institutions is that they are very
likely to suggest some kind of solution, even if the underlying conﬂict is not
squarely addressed. This was the case here: the WTO Appellate Body
ultimately upheld the Panel’s main ﬁnding, namely that the EC’s import
ban did indeed constitute a violation of WTO law (WTO 1998: paragraph
It would go beyond the conﬁnes of this article to go into the depths of the SPS Agreement
and its interpretation. For an overview, see Koebele (2007).
E.g. whether the expression ‘based on’in art 3.1 SPS Agreement ought to be understood as
‘conforms to’(WTO 1998: paragraphs 20–2, 46, 160–6) or whether the term ‘examination and
evaluation of available scientiﬁc information’required by art 3.3 SPS Agreement (fn 3) entails a
risk assessment in accordance with art 5.1 SPS Agreement (WTO 1998: paragraphs 23, 47,
International law as a common language across spheres of authority? 335
253). In fact, situations in which international courts decline to decide a
dispute are rare and almost never occur in contentious proceedings.
the jurisdictional and admissibility thresholds are passed, courts and court-
like institutions will suggest a solution, and they will do so by using legal
interpretative and argumentative techniques.
This does not mean that international law provides a single answer for all
or even most cases of interface conﬂict. The use of legal interpretative and
argumentative techniques does not unequivocally yield one single solution,
as the above example shows. Rather, international law provides a speciﬁc
type of conﬂict management, a common language that is characterised by its
formalism. Such a solution will always be of an interim nature, as it will
never solve the underlying substantive political interface conﬂicts (ILC
2006b: paragraphs 487–8; Krisch 2010: 23). A legal solution provided
by a court cannot provide a solution on exclusively substantive consider-
ations: even if the solution is a substantive one, the court, in justifying it, will
need to do so within the conﬁnes of its procedural and argumentative
V. Does legal form matter? On the authority of international law and
limited claims to universality
If courts and court-like institutions are seldom in a position to provide a
permanent solution on exclusively substantive grounds, why bother with
legal argument in the ﬁrst place? Any attempt at an explanation will
certainly involve a number of factors, ranging from historical evolution,
to political choices by states, and states becoming increasingly used to
resorting to legal arguments and legal instruments (Alter 2014: 154–8).
But what is the speciﬁc appeal of formal international law? In this contri-
bution, I have sought to show that international law’s argumentative rules,
understood as a common formal language (Koskenniemi 1990,2001), a
nomos (Cover 1983), might provide some form of coherence that cuts across
spheres of authority and substantive normative orders (cf. also Möllers
2017). At the same time, it has also become clear that legal solutions are
Perhaps the most prominent case is the 1996 Advisory Opinion by the ICJ on the legality of
the threat or use of Nuclear Weapons in which the ICJ came close to declaring a non liquet
(ICJ 1996)–but which was an advisory opinion, not a contentious case.
Balancing and proportionality are the two techniques where substantive goals ﬁnd their
place, but these stand at the end of litigation, not at its beginning. For a survey of those techniques
in international economic law and on the legitimacy problems because of the precedential value
that such exercises inevitably entail see Kleinlein (2012b).
336 hannah birkenko
far from absolute: often, they are but one instance in a broader interface
I shall conclude with a few reﬂections on international law’s authority.
When justifying one’s conduct with reference to a norm of international law,
there is an expectation that this norm –unlike a non-legal norm –will have a
form of augmented authority qua being law. International law, like all law,
puts forward a claim to authority in its quality as law. Perhaps most
importantly, the claim of law’s authority via its nature as law is distinct
from its claim to authority based on the morality of its content (Besson 2009:
While we might have moral reasons to follow the substantive
content of a law, there might also be moral reasons that are a counterweight
to one’s obligation to follow a law, e.g. when the law prescribes to torture
Beyond the distinction between law and morality, there is a more general
distinction between law and non-law. In the context of constitutional
requirements for law-making beyond the state, Klabbers (2009: 108) has
pointed out that law should be cognisable as such, in order to distinguish
between the kinds of reasons that are acceptable in legal argument, and
reasons that are not acceptable. This also holds in times of ever-increasing
‘soft law’and ‘informal law’. Those who, like Prosper Weil (1983: 415–16),
have lamented that there is no longer a clear distinction between interna-
tional law and ‘prenormative acts’, do so on the basis that a distinction is in
principle possible (and in practice desirable). Others, who, like Alvarez
(2005) consider law to be anything that yields ‘normative ripples’and fulﬁls
certain legitimacy requirements, would like to expand the realm of what is
considered to be legal. But the underlying distinction between law and non-
law always remains intact. What is at stake is where to draw the line, not
whether the line ought to be drawn in the ﬁrst place.
By presenting a speciﬁc norm that is associated with or originates within a
sphere of authority as a norm of international law, the association with that
particular sphere of authority is loosened to the beneﬁt of a more general
form of authority associated with being law. Let’s consider the example of
the precautionary principle as a norm within the sphere of authority of
environmental protection. Norms from that sphere of authority draw their
authority primarily from the common social purpose –environmental
In addition to the question of whether there is a moral duty to obey the substantive content
of the law, Besson further distinguishes her project of carving out a notion of authority of
international law from the questions of whether there is a legal duty to obey the law, whether
the law’s subjects consented to the norm in question, and lastly whether the law is in fact obeyed.
As Benhabib (2006: 158–9) has emphasised, it is important to distinguish law from
morality precisely in order to be able to criticise legal norms for their immorality, an argument
that can be traced back to Kelsen.
International law as a common language across spheres of authority? 337
protection –being a legitimate social purpose, perhaps even a common
global good. When we present the precautionary principle as a norm of
customary international law, we require actors to follow it not on the basis
of solely substantive considerations (because it is desirable to do so), but
because it exercises authority qua law. This authority qua law is substan-
tively empty, and because it is substantively empty, it ‘represents the possi-
bility of the universal’(Koskenniemi 2001: 504). The universality claim only
holds insofar as we appeal to a norm as a legal norm, and does not extend to
its content (ibid).
I am not suggesting that this kind of authority is somehow normatively
superior than appeals to other forms of authority, e.g. moral or utilitarian,
or other functional considerations. Likewise, it is not clear that courts and
court-like institutions are inclined to appeal to law’s authority alone. In
particular those courts or court-like institutions that are institutionally
rooted in a given sphere of authority might instead appeal to the social
purpose towards which the sphere of authority is geared. Such courts have
also been labelled ‘regime courts’(Shany 2012: 29). One question for further
research would thus be whether there is a difference in how legal argument is
being used when comparing international courts and court-like institutions
that are clearly part of one designated sphere of authority, such as the WTO
Dispute Settlement Mechanism’s Appellate Body or the European Court of
Justice, and international courts that are not assigned to one particular
sphere of authority, most importantly the International Court of Justice.
Another question of interest might be to investigate when and how actors
resort to international legal arguments outside of the courtroom, and
whether such a resort would only touch upon the ‘solution’dimension. In
front of courts, actors dress their interface conﬂicts in legal terms because
this is what is required in order to be able to resort to a third-party actor to
begin with. To explore whether actors use legal argument without this
constraint might give us a hint as to how strongly the authority of law
qua law is perceived. This might constitute fertile ground for further
I would like to thank two anonymous reviewers, the members of the
Research Group ‘Overlapping Spheres of Authority and Interface Conﬂict’
and Gabriele Wadlig for valuable comments on previous drafts, as well as
Defne Tuner for excellent research support.
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