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1.       Introduction

international law is made largely on a decentralised basis by the actions of
the 192 States which make up the international community.1
Unlike national legal systems, International Law does not have a clear
normative hierarchy of sources of law and legal norms2
and the jurisdiction of International Court of Justice is dependent upon the
consent of States. Its nature, therefore, means that the sources of
international law are much more diverse than those found in national legal

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One of the
sources of international law, jus cogens – or peremptory norms – refer to
certain fundamental, overriding principles of international law from which no
derogation is ever permitted.3
Its existence was only accepted after a significant opposition from the Western
upon its initial introduction in Vienna Convention5.
Although nowadays the existence of the concept of jus cogens is commonly
accepted, it is still not clear which norms belong to it6,
or whether it does, indeed, constitute the highest hierarchical category of
norms in international law.

It is important
to note that there are various contradicting theories on the issue of hierarchy
of international law’s sources. Therefore, reaching a definite conclusion as to
whether this hierarchy exists and – if it does – which source prevail over the
other is extremely difficult. In this essay, therefore, it will be not
confidently confirmed as to whether jus cogens is the highest hierarchical
category of norms. Instead, the conclusion reached will be based on the
popularity of theories. Three points will be agreed on: there is an evidence of
informal hierarchy of the sources in international law; many academics believe
that jus cogens norms are the core values of international community, and;
there is an agreement among many scholars that jus cogens constitute the
highest hierarchical category of norms in the international system.

To reach these
conclusions, this essay will examine few very important points relating to the
hierarchy of sources in international law. Firstly, it will be asserted whether
there is an evidence of hierarchical order of sources of international law in
relation to Article 38 ICJ. Secondly, these sources – namely treaties and
customs -will be contrasted with one another to ascertain whether such
hierarchy exists and, if so, which one of these sources prevails. Thirdly,
treaties and customs will be compared with jus cogens norms and the position of
some of the academics on the concept of jus cogens as hierarchically superior
will be examined. Lastly, the position of legal academics on whether jus cogens
norms represent the core values of international community will be briefly

2.       The existence of hierarchy between the sources
of international law in Article 38 ICJ

The sources of
international law can be found in Article 38 of Statute of the International
Court of Justice (ICJ)7, an
international treaty annexed to the UN Charter. Although this document is just
a direction to the International Court of Justice, it has been commonly
accepted as an authoritative statement concerning the formal sources of
international law8. Article
38 identifies five sources: principal (treaties and customs), complementary
(general principles of law) and subsidiary (judicial decisions, doctrine and the
writings of “the most highly qualified publicists”).9
It is important to note that this list is no longer thought to be complete, but
it still provides a useful starting point when looking for the list of sources
of international law10.

The first thing
that needs to be asserted is whether Article 38 suggests that there is a
hierarchy of sources. Due to the unusual nature of international law – such as
the lack of a centralised and hierarchically structured law-making – sources of
international law are usually said to be of equal status. This means that the
norms derived from one source are not more important than the norms derived
from another source.11
Some scholars noted, however, that the specific sequence in which these sources
are listed in Article 38 may suggest a hierarchy.12
 The hierarchy of sources, as set in the
Article – treaties prevailing over custom, and customary law prevailing over
general principles – was also advocated during the drafting of Article 38.13
This proposal was rejected, however, and the order of sources in Article 38 is
thought to be of no legal relevance – with the exception of judicial and jurist
writings, which are identified to be subsidiary and law examining, rather than law
determining. Accordingly, it can be argued that the Statue, in a sense, does
provide a hierarchy of sources in which treaties and custom prevail over
general principles and other sources.

Consequently, it
is important to note that also States and legal scholars have expressed clear
preferences for particular sources, consequently establishing informal
hierarchies.14 Most
scholars regard treaties and customs standing as the only true sources of law,
while the judicial decisions and doctrinal writings are said to serve only for
the interpretation of existing norms.15

Beyond these
preferences, however, the consensus remains among most scholars and judges that
Article 38 does not establish a rigid hierarchy of sources, particularly
between customary law and treaties. These are said to exist alongside each
other in – as argued by Prost – ‘no
particular order of pre-eminence, in a decentralized arrangement where no
source ranks higher than the other’.16

This idea of the
lack of hierarchy of the sources of international law was further supported by
academics such as Hart, for example, who believes that international law did
not form a hierarchy between primary and secondary rules, meaning that the
sources are of equal legal standing. Hart argued that all of the sources of
international law are of law determining nature, and there is no rule of

Finally, the categorisation
of the judicial decisions as a merely subsidiary law in Article 38 is thought
to be incorrect. This idea relies on ‘autocatalytic process’ in which the ICJ depends
on the writings of International Law Commission to come to their judgements,
who in turn relies on the ICJ to describe what the law is.  This, in turn, leads to a process where new
rules of law are created by a ‘mutual reaffirmation’.18
This was confirmed by some of the judges of the International Court of Justice
who admitted that, rather than simply identifying and applying the pre-existing
law, they create a new law – an example of which can be the development of the
law on maritime delimitation.19
This would suggests that the scholar writings are of the same importance as,
for an instance, treaties.

To conclude this
section, it can be argued that although there is no normative hierarchy of
sources in international law, the judges and scholars did, indeed, create an
informal hierarchy of sources. This is evident in both case law and many
theories referring to treaties and/or customary law prevailing over one


Customary International Law

The origins of
international law are found in customary international law (CIL) and defined as
‘a constant and uniform usage, accepted as law’.20

CIL enables
international law to evolve directly from the conduct of States, which seems to
be well suited for the decentralised structure of international law. For such
conduct to provide the basis for CIL rule, a significant number of States need
to participate in the practice which must be both ‘extensive and uniform’21; as
well as amount to a consistent pattern of behaviour and be ‘generally
consistent’22.  It
is also necessary that States believe that they are under a legal obligation to
follow a particular practice (opinion juris), as if the State objects to it
from the moment of its establishment, it will not be bound by that rule.23


Treaties are
legally binding agreements that commit the parties to follow a particular
course of conduct by reference to rights and/or obligations. ‘Treaty contracts’ often involve a
small number of States and are usually concerned with technical or commercial

Relationship between treaty law and

Firstly, it is important
to note that three theories on the topic of superiority of one source over
another will be examined in this section. The first theory suggests that the
treaties and customary law are of equal legal standing; the second theory
suggests that treaties prevail over customary law, while the third and last theory
argues that customary law prevails over treaties. It is, therefore, particularly
difficult to decide which theory is correct.

As mentioned
before, in the classical understanding of international law customary law and
treaties are thought to be of equal authority,24
with no hierarchy between them.25
Hart is also a fierce challenger of the idea that one source can be regarded as
more important than the other source.26

Although in
traditional view there is no hierarchy between sources of law, for the purpose
of this essay, as established previously, it will be agreed that an informal
hierarchy does exist. The idea that informal hierarchy exists in international
law, however, does not mean that one of the main sources of law – treaties or
customary law – have to prevail over one another. Indeed, this hierarchy may
simply mean that the primary sources are legally superior to the secondary
sources, which are thought to be simply law recognising rather than law

In theory,
therefore, in a situation where CIL and treaty law cover the same issue both
sources will coexist. In reality, however, as seen in the case law, in such
situation a treaty will prevail, but the CIL rule will not disappear and will
be applied if the treaty become inapplicable for any reason.27  This suggests that although, theoretically,
both sources are of equal importance, in practice treaties are held to be of
bigger significance.

To further
support above point, it is often argued to be the case that custom is meant to
fill the gaps between treaties; the treaty obligations of the parties being the
primary point of reference for determining the applicable international law.28
 The ICJ has stated on several occasions
that ‘in general it would not be
appropriate that a State should bring a claim based on a customary-law rule if
it has by treaty already provided means for settlement on such a claim’.29

Although the
point above suggests that judges display a clear preference towards treaty law
being more important than customary law, it is essential to remember that this
may be due to the fact that most treaties were developed after customary law.
Consequently, it is unclear as to which one would have a priority where a rule
of customary law is developed after the formation of a treaty. In theory,
however, it can be argued that if such situation was to occur and the treaty would
still have priority, the sequencing of the sources in Article 38 would be
hierarchically accurate. If the later rule of custom would override the treaty
– keeping in mind that so far the treaties were prioritised by the courts –
this would imply that custom and treaties are actually of equal rank.

It is important
to note, however, that the International Court of Justice has made every effort
to avoid treaties coming into conflict with later customary norms by
interpreting treaties to complement the customary rule rather than contradict
Although this may suggest that the customary law is regarded to be of the same
significance as the treaties, it is unclear as to what would happen if the
later customary law and treaty law were so contradicting that interpreting them
as complementing each other would be simply impossible.

Finally, the
last theory suggests that customary law may, actually, be of higher
significance than treaties. As argued by Gulgec, the principle of pacta sunt servanda – which states that
agreements, such as treaties, must be upheld by all the signatories – lies at
the foundation of international law with no superior or more fundamental
positive norm than this principle. This norm itself is a customary norm, and
the validity of international treaties stem from its principle. Gulgec argues
that as treaties are formed from customary law, international treaties and
customary norms cannot be considered to hold the same hierarchical power.
Gulgec argues that due to this reason customary norms are hierarchically

To go over the
main points, as it can be seen from the above points, the theories concerning
the significance of treaties and customs are very diverse. Although all seem to
be convincing in theory, ICJ seems to give priority to the treaties in
practice. This suggests that, in practice, treaties do prevail over customary

Of course, this
does not mean that treaties are the highest source of international law. Jus
cogens norms are said to be hierarchically superior to all of the other sources
of international law, which will be discussed in subsequent headings.


Whether Jus cogens norms represent the
core values of international community

Before this
essay will move on to discuss the hierarchical superiority of jus cogens over
other sources of international law, the statement contained in the question –
‘jus cogens represents the core values of international community’ – must be examined

Jus cogens (or
peremptory norms) of international law are those rules that have acquired a
higher status in international law, as argued by some academics, because ‘they exist to protect the values and
interests that are fundamentally important to the international community as a
whole’.32 The
ILC Special Rapporteurs Lauterpacht and Fitzmaurice33
agree that jus cogens norms are ‘expression of international community’, which –
in turn – is the most usual explanation of its peremptory character.34

Furthermore, it
is worth mentioning that some academics argue that the idea that jus cogens
norms represent core values of the international community stems from the
difficulty of a norm achieving that status, as the procedure envisaged by
Article 53 for the creation of jus cogens norms is very ambiguous.35
Article 53 states that peremptory norms: ‘can
be modified only by a subsequent norm of general international law having the
same character’. In other words, they can only be changed by the
development of a new peremptory norm. It is extremely
difficult to change peremptory norms, and it is equally as difficult to
introduce a new jus cogens norm. The question remains as to whether this is due
to the fact that only the core values of international community should be
considered as peremptory norms, or is it just a safety valve given the
potential implications of the misuse of this superior category of legal norms?36

Additionally, some
academics argue that the idea that jus cogens norms represents the core values
of international community stems from the fact that most rules recognised to
have achieved the status of jus cogens relate to human rights: the prohibitions
of aggression37,
slavery, racial discrimination, crimes against humanity and torture39,
and the right to self-determination.40

To conclude, it
is widely accepted that jus cogens norms represent the core moral values of the
international community. However, this topic is rarely analysed and most
scholars simply state this as a matter of fact in their works.

5.       Jus cogens norms – hierarchically superior?

As to the
hierarchical status of jus cogens: this topic has remained rather vague. The uncertainties
surrounding the hierarchical status of jus cogens are reflected in the fact
that it is actually very rare for jus cogens to have been successfully invoked
in a court to resolve a norm conflict.  Moreover, both domestic and international
courts seem to be very reluctant to draw any conclusions from the hierarchical
superiority of peremptory norms over any other rule of international law. It
seemed that the International Court of Justice (ICJ) has refused – until
recently – to discuss the existence of such normative category.41

peremptory norms are often regarded as the only true instances of hierarchy in
international law.42
This, and the theories opposing this idea, will be discussed in subsequent
subsections relating to jus cogens norms by comparing them with treaties and
customary law.


cogens in treaty law

Notably, the key
instrument supporting the hierarchical supremacy of jus cogens norms, the
Vienna Convention, states that ‘a treaty
is void if, at the time of its conclusion, it conflicts with a peremptory norm
of general international law (…) from which no derogation is permitted’.43  Under this view, international law recognizes
peremptory norms as “hierarchically superior to ordinary conventional and
customary law in order to promote the interests of the international community
as a whole.”44

Some believe,
however, that Articles 53 and 64 of the Vienna Convention do not apply to
non-treaty acts, as Articles only refer to the voidness of treaties conflicting
with jus cogens norms.45
Consequently, although this would suggest that jus cogens norms are
hierarchically superior to the treaties, it is unclear where it would leave
other sources of international law. The approach, however, is not widely held
with some academics arguing that it is simply incorrect. Although the Vienna
Convention only provides for voidness of treaties – it is commonly accepted
that the effects of peremptory norms are not limited to the validity of
This was also supported by Professor Meron, who said that “jus cogens
principles apply not only to treaties,” but also to “any other act or action of

At the same time the notion that jus cogens is hierarchically
superior to the treaties was similarly conveyed by academics such as Kelsen who
states that ‘jus cogens represents a
category of norms owing its legal existence to customary international law
which stand as the hierarchical superior of international treaties and cannot
be derogated by such treaties or any norm of international law other than a
subsequent jus cogens norm’.48  This approach proposes that jus cogens norms are
based somewhere between customary law which is hierarchically superior, and
treaty law. Moreover, this approach suggests that jus cogens norms, although
superior to treaty law and other sources of international law, is generally
inferior to the customary law.

Finally, the last theory argues that suggesting that jus
cogens norms are superior to the treaties would be logically incoherent, as the
concept of jus cogens is rooted in the Vienna Convention. This is due to the
fact that the norm is thought to be superior of the other when it regulated the
other’s conditions of validity and the inferior norm derives its validity from
the superior one. It can be only argued, therefore, that the concept of jus
cogens have the primacy of application over treaty provisions. As a result, we
can conclude that the concept of jus cogens as it is defined and regulated in
the Vienna Convention cannot be based on treaty law and that if such a category
exists it needs to stem from customary international law.

To conclude, it
is universally thought that jus cogens norms are hierarchically superior to the
treaties. The academics provide various explanations for the superiority of jus
cogens norms over the treaties, but there is a less of an agreement on whether jus
cogens is superior to all the norms in international law or treaties only.


cogens in customary international law

As argued
before, some academics argue that jus cogens norms are merely a strengthened
form of custom.49
David Kennedy, for example, argued that jus cogens is not a peremptory norm,
but simply a ‘super-customary norm’, which cannot be derogated from.50
This suggests that jus cogens norms are hierarchically located between
customary international law and international treaties. Most importantly, and
very controversially, Gulgec argued that jus cogens norms are actually
hierarchically inferior to customary international law,  but a primacy of application is granted to jus
cogens norms over any customary rule.51  This suggests that jus cogens norms do not
constitute the highest hierarchical order of norms in international law. This
idea was expanded by other academics, such as Czaplinski, who claims that jus
cogens norms can only be created by way of custom. Therefore, if it is
conceived that jus cogens norms are created by way of custom, it can be argued
that they “are” customary international law and therefore there
cannot be a hierarchy between jus cogens norms and other customary rules of
international law. This is due to the fact that the norms created through the
same procedure needs to be of equal hierarchical level.

In conclusion,
it seems that jus cogens norms, although not superior to the customary law, are
given a priority due to the fact that they cannot be derogated from. This,
therefore, suggest that jus cogens norms are hierarchically superior to the
customary law.

1.       Conclusion

In conclusion,
as seen from above essay, it is difficult to establish the exact hierarchy of
the sources of international law. There seems so be a general consensus,
however, that jus cogens norms are, indeed, hierarchically superior to other
sources of international law due to the priority they are given to other norms
of international law.

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