Public International Law – Complete Summary
Week 1 – The Law-Making Process and the Sources of International Law
Learning Objectives
1) Understanding the sources of international law
Article 38(1) of the ICJ Statute lays out the following sources of international law:
(a) International treaties (or conventions), whether general (multilateral) or particular (between a
smaller group of states);
o Treaties are formal instruments trough which states can agree that certain obligations will be
binding on them. The existing customary rules on Treaties have been codified in the VCLT (see
week 2).
(b) International custom, “as evidence of a general practice accepted as law”;
o General / material practice by states: the action or inaction of states in their relations with each
other, or in relation to recognised international actors.
o Opinio Juris: evidence of “acceptance as law” by states, exemplified by the Continental Shelf case:
“the passage of only a short period of time is not necessarily a bar to the formation of a new rule
of custom […] an indispensable requirement would be that within the period in question, state
practice, including that of states affected, should have been both extensive and virtually uniform”.
International Law allows for situations where the application of a customary legal rule is not
universal:
“Persistent and Subsequent Objection”: Where a state demonstrably objects to the
emergence of a new rule or the modification of an existing one – provided that its
objection is acquiesced by other states – it will not be bound by the new rule. However,
in Anglo-Norwegian Fisheries, the ICJ ruled that an existing customary rule would not
apply to a state if (1) it objected to the application of the rule to itself (2) at the initial
stages, and (3) in a consistent manner.
“Local, regional and bilateral custom”: In the Asylum and Right of Passage cases, the ICJ
confirmed the existence of custom that only applies to a sub-set of states.
(c) General principles of law, “recognised by civilised nations”;
o General Principles aspire to provide closure to the international legal system, to aid in the
interpretation of other primary sources in novel situations, and to ensure that every international
situation can be determined as a matter of law.
(d) Subsidiary means for the determination of rules of law, i.e. judicial decisions and “teachings of the
most qualified publicists”.
o Article 38(1)(d) enumerates judicial decisions and writings of the most eminent publicists as
subsidiary means of law, as they rely on the formal sources of law to develop arguments.
2) Explaining the processes of international law-making and the role of non-state actors in such processes
“Law-making Treaties”: Multilateral conventions that create a regime of legal rules of general
application, such as conventions on human rights and armed conflict.
Resolutions of the Security Council: Though not formally a law-making organ, the UNSC has the power
to create international legal obligations binding on all states. Moreover, under Article 103 of the UN
Charter, obligations created by the Council will prevail over obligations under any other international
agreements in the case of a conflict.
3) Understanding the relationship between the sources of international law
Overlap: A Treaty covering the same grounds as a rule of custom?: In Nicaragua, the ICJ rejected the
idea that existing custom would be superseded or absorbed into a Treaty. An existing customary rule
will thus continue to exist irrespective of the adoption of the Treaty rule, as two rules with the same
content may be subject to different principles of interpretation and application.
Three kinds of effects of Treaty Law:
o Declaratory effect: Codification of pre-existing rules of customary international law
o Crystallising effect: Codification of an emerging practice
1
, o Constitutive effect: The Treaty generates a practice that leads to the creation of a customary
rule among signatory and non-signatory states.
4) Engaging with the question of a (putative) hierarchy of norms
Hernández: Article 38(1) suggests that Treaties, customary law, and general principles (a, b, and c)
enjoy primacy over the subsidiary means of determining the law(d). Formally speaking there is no
hierarchy between the former three (the ‘primary’ sources), though the ‘general principles’ were
inserted in the Statute if the PCIJ as a fall-back source of law, which was confirmed in Nicaragua.
o Conflicts can be resolved on the basis of the principles of “specific rules prevail over rules of
general application” and of “more recent law prevails over an inconsistent earlier law”.
o Moreover, peremptory norms (jus cogens), are regarded as possessing a higher status to
“ordinary” rules of international law and would prevail over them in case of conflict. This has
been codified in Article 53 VCLT, which provides that no derogation is permitted from such a
norm is permitted, and, together with Article 64 VCLT, it provides that Treaties that are in
conflict with such norms shall be void.
Vidmar: The concepts of obligations erga omnes (‘owed to all’) and norms of jus cogens show that
international law does embrace the concept of the international value system, but it remains unclear
whether it also supports hierarchically superior norms of a constitutional character.
o Chapter VII UN Charter: allows the Security Council to override national sovereignty by taking
legally binding measures in case of a “threat to peace” and by authorising the use of force as an
exception to the prohibition in Article 2(4) on the use of force.
o Article 103 UN Charter: elevates the UN Charter to the status of superior international Treaty, as
it states that if conflict arises between obligations of UN Members under the UN Charter and
obligations under other international agreements, the former prevails.
o Norms of Jus Cogens: prevail over a Chapter VII Resolution, as mentioned by judge Lauterpacht
in Bosnian Genocide, as the SC cannot create obligations that are incompatible with peremptory
norms. Moreover, Treaties that conflict with such norms are void under Article 53 and 64 VCLT.
5) Discussing the debate on unity or fragmentation in international law
The fragmentation of public international law is a long-observed phenomenon that demonstrates
uneven normative and institutional development and evolution in inter-state relations. Separate legal
norms and institutions have developed largely independently from one another, often instigated by
non-identical groupings of states and in response to specific functional issues.
6) Discussing the concept of ‘soft law’ and its potential role in the law-making process
“Soft Law”: Soft law is the name given to the body of standards, commitments, declarations, policy
guidelines, codes of conduct and other instruments which do not impose legally binding obligations on
states or other legal actors. However, such instruments do have the potential to contribute to the
development of “hard law”, i.e. legally binding measures.
Most important case law
Case Ruling
Nicaragua v The ICJ rejected the idea that existing custom would be superseded or absorbed into
United States Treaty law. An existing customary rule will thus continue to exist irrespective of the
[1986] adoption of the Treaty rule, as two rules with the same content may be subject to
different principles of interpretation and application
The ICJ considered the prohibition on the aggressive use of force – a violation of Article
2(4) of the UN Charter – a peremptory norm, except in cases of self-defence (Article 51)
and in cases that do not cross a certain threshold of an armed attack
Anglo-Norwegian Concerning the “Persistent Objector” rule, the ICJ ruled that an existing customary law
Fisheries rule would not apply to a State if (1) it objected to the application of the rule to itself (2)
Jurisdiction at the initial stages and (3) in a consistent manner.
[1978]
2
Week 1 – The Law-Making Process and the Sources of International Law
Learning Objectives
1) Understanding the sources of international law
Article 38(1) of the ICJ Statute lays out the following sources of international law:
(a) International treaties (or conventions), whether general (multilateral) or particular (between a
smaller group of states);
o Treaties are formal instruments trough which states can agree that certain obligations will be
binding on them. The existing customary rules on Treaties have been codified in the VCLT (see
week 2).
(b) International custom, “as evidence of a general practice accepted as law”;
o General / material practice by states: the action or inaction of states in their relations with each
other, or in relation to recognised international actors.
o Opinio Juris: evidence of “acceptance as law” by states, exemplified by the Continental Shelf case:
“the passage of only a short period of time is not necessarily a bar to the formation of a new rule
of custom […] an indispensable requirement would be that within the period in question, state
practice, including that of states affected, should have been both extensive and virtually uniform”.
International Law allows for situations where the application of a customary legal rule is not
universal:
“Persistent and Subsequent Objection”: Where a state demonstrably objects to the
emergence of a new rule or the modification of an existing one – provided that its
objection is acquiesced by other states – it will not be bound by the new rule. However,
in Anglo-Norwegian Fisheries, the ICJ ruled that an existing customary rule would not
apply to a state if (1) it objected to the application of the rule to itself (2) at the initial
stages, and (3) in a consistent manner.
“Local, regional and bilateral custom”: In the Asylum and Right of Passage cases, the ICJ
confirmed the existence of custom that only applies to a sub-set of states.
(c) General principles of law, “recognised by civilised nations”;
o General Principles aspire to provide closure to the international legal system, to aid in the
interpretation of other primary sources in novel situations, and to ensure that every international
situation can be determined as a matter of law.
(d) Subsidiary means for the determination of rules of law, i.e. judicial decisions and “teachings of the
most qualified publicists”.
o Article 38(1)(d) enumerates judicial decisions and writings of the most eminent publicists as
subsidiary means of law, as they rely on the formal sources of law to develop arguments.
2) Explaining the processes of international law-making and the role of non-state actors in such processes
“Law-making Treaties”: Multilateral conventions that create a regime of legal rules of general
application, such as conventions on human rights and armed conflict.
Resolutions of the Security Council: Though not formally a law-making organ, the UNSC has the power
to create international legal obligations binding on all states. Moreover, under Article 103 of the UN
Charter, obligations created by the Council will prevail over obligations under any other international
agreements in the case of a conflict.
3) Understanding the relationship between the sources of international law
Overlap: A Treaty covering the same grounds as a rule of custom?: In Nicaragua, the ICJ rejected the
idea that existing custom would be superseded or absorbed into a Treaty. An existing customary rule
will thus continue to exist irrespective of the adoption of the Treaty rule, as two rules with the same
content may be subject to different principles of interpretation and application.
Three kinds of effects of Treaty Law:
o Declaratory effect: Codification of pre-existing rules of customary international law
o Crystallising effect: Codification of an emerging practice
1
, o Constitutive effect: The Treaty generates a practice that leads to the creation of a customary
rule among signatory and non-signatory states.
4) Engaging with the question of a (putative) hierarchy of norms
Hernández: Article 38(1) suggests that Treaties, customary law, and general principles (a, b, and c)
enjoy primacy over the subsidiary means of determining the law(d). Formally speaking there is no
hierarchy between the former three (the ‘primary’ sources), though the ‘general principles’ were
inserted in the Statute if the PCIJ as a fall-back source of law, which was confirmed in Nicaragua.
o Conflicts can be resolved on the basis of the principles of “specific rules prevail over rules of
general application” and of “more recent law prevails over an inconsistent earlier law”.
o Moreover, peremptory norms (jus cogens), are regarded as possessing a higher status to
“ordinary” rules of international law and would prevail over them in case of conflict. This has
been codified in Article 53 VCLT, which provides that no derogation is permitted from such a
norm is permitted, and, together with Article 64 VCLT, it provides that Treaties that are in
conflict with such norms shall be void.
Vidmar: The concepts of obligations erga omnes (‘owed to all’) and norms of jus cogens show that
international law does embrace the concept of the international value system, but it remains unclear
whether it also supports hierarchically superior norms of a constitutional character.
o Chapter VII UN Charter: allows the Security Council to override national sovereignty by taking
legally binding measures in case of a “threat to peace” and by authorising the use of force as an
exception to the prohibition in Article 2(4) on the use of force.
o Article 103 UN Charter: elevates the UN Charter to the status of superior international Treaty, as
it states that if conflict arises between obligations of UN Members under the UN Charter and
obligations under other international agreements, the former prevails.
o Norms of Jus Cogens: prevail over a Chapter VII Resolution, as mentioned by judge Lauterpacht
in Bosnian Genocide, as the SC cannot create obligations that are incompatible with peremptory
norms. Moreover, Treaties that conflict with such norms are void under Article 53 and 64 VCLT.
5) Discussing the debate on unity or fragmentation in international law
The fragmentation of public international law is a long-observed phenomenon that demonstrates
uneven normative and institutional development and evolution in inter-state relations. Separate legal
norms and institutions have developed largely independently from one another, often instigated by
non-identical groupings of states and in response to specific functional issues.
6) Discussing the concept of ‘soft law’ and its potential role in the law-making process
“Soft Law”: Soft law is the name given to the body of standards, commitments, declarations, policy
guidelines, codes of conduct and other instruments which do not impose legally binding obligations on
states or other legal actors. However, such instruments do have the potential to contribute to the
development of “hard law”, i.e. legally binding measures.
Most important case law
Case Ruling
Nicaragua v The ICJ rejected the idea that existing custom would be superseded or absorbed into
United States Treaty law. An existing customary rule will thus continue to exist irrespective of the
[1986] adoption of the Treaty rule, as two rules with the same content may be subject to
different principles of interpretation and application
The ICJ considered the prohibition on the aggressive use of force – a violation of Article
2(4) of the UN Charter – a peremptory norm, except in cases of self-defence (Article 51)
and in cases that do not cross a certain threshold of an armed attack
Anglo-Norwegian Concerning the “Persistent Objector” rule, the ICJ ruled that an existing customary law
Fisheries rule would not apply to a State if (1) it objected to the application of the rule to itself (2)
Jurisdiction at the initial stages and (3) in a consistent manner.
[1978]
2
