At its most abstract level, international law concerns norms that govern the
conduct of States and the relations between them. That isn't to say that
international law's reach does not go beyond the rights and obligations of
States. It is recognised that individuals may incur responsibility under
international law, while corporations have not been left untouched either.
Additionally, over the last century, international organisations have played an
increasingly important role in the development of international law.
Nevertheless, States continue to be the main subjects of international law. Any
system of law must have sources. For instance, in Israeli law, Knesset
legislation, government regulations and judicial precedents, among others, serve
as binding sources of law.
As for international law, while its main sources are
clear, as shall be demonstrated below, the process of identifying them is
sometimes more complex. The most accepted statement of the sources of
international law may be found in Article 38(1) to the Statute of the
International Court of Justice (ICJ). The ICJ Statute is to a large degree
reproduction of the Statute of the Permanent Court of International Justice, the
ICJ's predecessor. Article 38(1) to the ICJ Statute states:
The Court, whose function is to decide in accordance with international law such
disputes as are submitted to it, shall apply:
- international conventions, whether general or particular, establishing
rules expressly recognized by the contesting states;
- international custom, as evidence of a general practice accepted as law;
- the general principles of law recognized by civilized nations;
- subject to the provisions of Article 59, judicial decisions and the
teachings of the most highly qualified publicists of the various nations, as
subsidiary means for the determination of rules of law.
As can be seen, there are three primary sources in international law: treaty,
custom and general principles of law. Additionally, there are two subsidiary
sources that may assist one in identifying norms derived from the primary
sources: judicial decisions and the teachings of the most highly qualified
publicists i.e. leading international law scholars.
Oppenheim defines the term source of law
as the name for a
historical fact out of which rules of conduct come into existence. The term
refers to methods or procedures by which international law is
created. The source may be formal (i.e. legal procedures and methods for the
creation of general rules) or material (i.e. actual materials providing evidence
of the existence of rules).
Oppenheim opined that there is only one source of international law viz. common
consent. Lawrence said that there is only one source of law i.e. consent of
nations. Consent may be either express or tacit (implied). Logically, therefore,
there are two chief sources of international law; Treaties (express consent) and
Customs (tacit consent).
Article 38 of the Statute of International Court of Justice:
- The Court, whose function is to decide in accordance with international
law, such disputes as are submitted to it, shall apply;
- International Conventions, whether general or particular, establishing
rules expressly recognized by contesting States.
- International Custom as evidence of general practice accepted by law.
- General principles of law recognized by civilized nations.
- Subject to provisions of Article 59, judicial decisions and teachings of
most highly qualified publicist of various nations, as subsidiary means for
determining the rules of law.
- This provision shall not prejudice the power of the court to decide a
case ex aequo et bono (considerations of fair dealing and good faith), if the
parties agree thereto (compromise, conciliation, etc.), which may be independent
of or even contrary to law.
A source Decisions or determinations of the organs of International
does not find mention in Art. 38 but it has now become a
well-recognized source. Some writers have mentioned additional sources of
international law viz. International comity, State papers, State guidance for
their officers, Reason equity and justice, Resolutions of international
conferences, Decisions of municipal courts on matters touching foreign nationals
or other States, etc.
Thus Article 38 is not exhaustive. If Art. 38 be simply
declaratory, it clearly cannot inhibit the emergence of new source of law,
brought into being by the development of the international community and its
progressive organization. Sources enumerated in Art. 38 are hardly adequate to
meet new challenges posed by today's world order. An authoritative order of the
use of sources of international law is given in Art. 38. Thus, the Court is
expected to apply the above sources in order in which they appear.
international conventions (i.e. treaties) shall be give preference by the court,
and in those cases where conventions are not available, they would be decided in
accordance with international custom. General principles of law shall find place
only where conventions and customs are not available. Judicial decisions and
teachings, etc. have been regarded as subsidiary means for the determination of
rules of law.
1. International Customs
It is the oldest and most original source of international law. Customary rules
of international law are the rules, which have been developed, in a long process
of historical development. Development or Formation of a Custom
(a) Custom and Usage: Custom is such a usage as has the force of law. Usage is
an international habit, which has yet not received the force of law. Usage
represents the twilight zone of custom, custom begins where usage ends.
States in their international relations start behaving in a particular way in
certain circumstances, it is expected that in the similar circumstances they
will behave in the same way (usage). But when this usage receives the general
acceptance of recognition by the States in their relations with each other,
there develops a conception that such a habit or behaviour has become right as
well as obligation of the State and in this way usage becomes the
Westlake defines custom as: that line of conduct which the society has
consented to regard as obligatory
A usage may or may not give rise to a custom. A usage crystallize into a custom
through the conduct of the States at the diplomatic level, actions or statements
of various States, foreign policy documents, speeches of delegates at
international conventions and conferences, practice of international organs like
the U.N., ICJ, etc. The decisions of municipal courts of States, military and
administrative tribunals in their deliberations and proceedings, following a
specific usage in practice, convert a usage into custom. The true test whether a
usage has crystallized into a custom is that it must be approved by the common
consent of civilized nations or general consensus of opinions.
Opiniojuris sine ncessitatis
According to Art. 38 of the Statute of ICJ, international custom should be the
evidence of general practice accepted as law
. This feeling on the part of
States that acting as they do, they are fulfilling legal obligations is called opiniojuris
(b) Generation of customary rules by treaty: A provision of a treaty may also
generate a rule of customary international law, as held in North Sea Continental
Shelf Case (1969) ICJ Rep.3.
In this case, the World Court observed:
The Right of Passage Case
- A treaty provision can generate customary international law, but only
when the provision concerned is of a fundamentally non-creating character
such as could be regarded as the basis of a general rule of law.
- The passage of only a short time period is not necessarily a bar to the
formation of a new rule of customary international law, however, an
indispensable requirement would be that within the period in question, State
practice (including that of States whose interests are specially affected),
should have been both extensive and virtually uniform in the sense of the
provision invoked; and should moreover have occurred in such a way as to
show a general recognition that a rule of law or legal obligation is
involved. Thus, opiniojuris must be present before a practice/usage is to become a customary
(ICJ Rep. 1960) demonstrates that a treaty provision
practiced for a long time may become a custom. The case illustrates that when in
regard to any matter or practice, two States follow it repeatedly for a long
time it becomes a binding customary rule. The case, like the Asylum case, made
it clear that local or regional custom, which derogates from general customary
law becomes binding only on States that support it.
Essential Ingredients of a Custom
According to Art. 38 of the Statute of ICJ, there are two requirements for the
existence of international custom, namely: firstly, there should be a
sufficiently uniform State practice; and secondly, the belief that such a
practice is obligatory (i.e. the opiniojuris).
In Pacquete Habana Case
Supreme Court, 1900), the court examined State laws and practices, treaties,
writings of publicists evidencing usage, and decisions of court, and held that
these materials uniformly proved the existence of a valid customary rule giving
immunity to small fishing vessels, honestly pursuing their calling, from
belligerent capture in time of war.
The Asylum Case (ICJ Rep. (1950)) shows that international law recognized the
existence of a special custom or local custom. The local or regional custom
which derogates from general customary law becomes binding only on States that
Generality of Practice
Although universality of practice is not necessary, the practice should have
been generally observed or repeated by numerous States. If a State acts in a way
prima facie incompatible with a recognized rule, but defends its conduct by
appealing to exceptions or justifications contained within the rule itself,
then, whether or not the State's conduct is in fact justifiable on that basis,
the significance of that attitude is to confirm rather than to weaken the rule
(Nicaragua Case, ICJ Reports, 1986).
Opiniojuris et necessitates: The S. S. Lotus Case (1927) demonstrates that the
opiniojuris is essential to the creation of a new customary rule of
Application of International Customs: Difficulties
The ICJ or any International Tribunal cannot suo-motu (i.e. on its own motion)
presume a custom as a guiding factor. It is quite difficult to establish an
international custom before such a tribunal because:
- the very existence of a custom must be proved,
- it has to be established that the custom in question has had a
continuous practice among a large number of States, and that too
consistently and without any break whatsoever or without any variation in
its practice, and
- it is very difficult to prove opiniojuris. For deducing this subjective
element, treaties, resolutions of General Assembly of U.N., international
conferences and statements of State representatives, etc. may be seen.
2. International Treaties In the modem period
International treaties are the most important source of international law.
Article 38 of the Statute of ICJ lists international conventions whether
general or particular, establishing rules expressly recognized by the contesting
as the first source of international law. The term convention
any treaty, convention, protocol or agreement, etc. Treaties may be classified
into following two categories:
- Law-making treaties: These treaties have a large number of
parties and create general or universal norms. These may be of two kinds:
those enunciating universal rules e.g. United Nations Charter, and those
laying down general rules e.g. 1958 Geneva Convention on the Law of the Sea,
Vienna Convention on the Law of Treaties, 1969, etc.
- Treaty-contracts: It is a treaty between two or only a few States
dealing with a special matter concerning these States exclusively.
A series or a recurrence of treaties laying down a similar rule may produce a
principle of customary international law. Further, subsequent independent
acceptance may generalize a treaty originally concluded between a limited
numbers of States. A treaty is therefore, of considerable evidentiary value as
to the existence of a rule, which has crystallized into law by an independent
process of development. International treaties are agreements of a contractual
character between States or Organizations of States creating legal rights and
duties (Oppenheim). According to Art. 2 of the Vienna Convention, 1969, A
treaty is an agreement whereby two or more States establish or seek to establish
relationship between them governed by international law. This does not mean
that other subjects of international law such as international organizations
cannot conclude treaties (Art. 3).
Pacta Sunt Servanda (Basis of the Binding Force of Treaties)According to Starke:
In nearly all the cases the object of the treaty is to
impose binding obligations on the States who are parties to it. Lauterpacht stresses:
treaties are legally binding because there exists a customary rule of
international law that treaties are binding.
Pacta sunt servanda
means States are bound to fulfill in good faith the
obligations assumed by them under treaties
(sanctity of contracts).
Vienna Convention on the Law of Treaties provides:Every treaty in force is binding upon the parties to it and must be performed
by them in good faith
(Art. 26). Art. 27 strengthen the rule by providing that no party to a treaty
might attempt to justify its failure to perform any of its international treaty
obligations by invocation of its internal law. Thus, perhaps the most
fundamental principle of international law and surely the basic principle of
treaties is pactasuntservanda.
Exceptions to the principle
When a new State comes into existence as a result of revolt, it does not
consider itself to remain bound by the treaties concluded by the Predecessor
State. The principle is also not applied when the obligations arising from the
treaty is related to that part of the territory which has been ceded/merged with
Rebus sic stantibus
(an implied clause in every treaty that provides that the
agreement is binding only so long as the material circumstances on which it
rests remain unchanged) is another important exception. Finally, pacta suntser
vanda is not an absolute principle for it fails to explain the binding force of
customary rules of international law.
Custom and Treaties:
Inter-relationship Custom and treaties are the two methods
for the creation of the legally binding rules ever since the beginning of the
international community. In both, consent of the States is reflected, and
therefore, they did not impose obligations on those States who did not wish to
be bound by them. However, while in customary rules, consent of the States is
implied, in the treaties, consent is express. Moreover, customary rules are
often not precise and adequate, while treaty-rules are clear and precise. This
has led to the transformation of many customary rules into treaty rules.
customary rules of international law cannot be regarded as to have ceased to
exist if they have been transformed into treaty rules. The court cannot be
prevented to apply customary rules in such cases. Thus, principles such as those
of the non-use, force, non-intervention, respect for the independence and
territorial integrity of States, etc continue to be binding as part of customary
international law, despite the operation of provisions of conventional law in
which they have been incorporated (Nicaragua Case,
ICJ. Rep. 1986).
existence of identical rules in international treaty law and customary law has
been clearly recognized in the North Sea Continental Shelf Cases. There is an
instance where custom has repealed treaty - law of the sea has witnessed repeal
of four Geneva Conventions of 1958 by the custom that emerged in the late 1960's
and 1970's, which was finally codified into the U.N. Convention on the Law of
Sea in 1982. The correct view is that treaty and custom have identical legal
force and are mutually reinforcing. These do not oppose each other but interact
and supplement each other. However, a treaty is superior to custom when there is
an apparent conflict between the two (S.S. Wimbledon Case, ICJ, 1923).
3. General Principles of Law
Article 38 (1) (c) of the Statute of ICJ lists General principles of law
recognized by civilized States' as the third source of international law
independent of custom or treaty. The phrase means principles as general as to
apply within all systems of law that have achieved a comparable state of
development. The rationality for the inclusion of general principles of law as
one of the sources of international law lies in the fact that a principle, which
has been found to be generally accepted by certain civilized legal systems, may
fairly presumed to be so reasonable as to be necessary to the maintenance of
justice under any system.
the rule of pactasuntservanda, that
contracts must be kept, the principle that no man may be a judge in his own
cause, the right of self defence, etc. The principles of law recognized by many
States do not become principles of international law automatically. They are
required to be recognized by the World Court.
Before the court applies any such principle, certain considerations are taken
- Firstly, a rule is a general principle of law, i.e. it is not limited in
- Secondly, the rule is recognized by most of the States of the world
The word recognized' presupposes the existence of the rule in the municipal
law. It may be noted that general principles of law include substantive as
well as procedural principles. Some general principles of law' common to
municipal legal systems are:
- Res judicata (a thing or matter settled by judgment): A matter once
judicially decided is finally decided, and there is an absolute bar to a
subsequent action involving the same claims, demand or cause of action. This
principle was taken into account in the U.N. Administrative Tribunal Case.
- Prescription (a claim to a right founded upon enjoyment): Eastern
Greenland Case (PCIJ, 1933), Island of Palmas Case.
- Subrogation (substitution or stepping into shoes of another): Mavrommatis
Palestine Concessions Case (PCIJ, 1925).
- Estoppel (preclusion): A State party to international obligation is bound
by its previous acts or attitude when they are in contradiction with its claims
in the litigation (Serbian and Brazilian Loan Case). The principle was also
applied in Temple of PreahVihar Case.
- Equity (reasonableness, fairness): The ICJ has been increasingly referring
to equity in its judgments in recent years viz. The Gulf of Maine Boundary Case,
North Sea Continental Shelf Cases.
- Other principles: The principle that every violation of an engagement
involves an obligation to make reparation (i.e. repair a wrong), is
recognized in Chorzow Factory Case.
Territoriality of criminal law recognized in S. S. Lotus Case. Status of General
Principles of Law Positivists claim that customs and treaties were the only
sources of international law as according to them international law is a body of
rules on which the States have given their consent.
However, the majority of international lawyers opine that the general principles of law
are a primary
source of international law because they are valid through all kinds of human
societies (Judge Tanka, dissenting opinion, South West Africa case ICJ, Rep.
1966). Lauterpacht has rightly remarked that the main function of the general
principles of law' has been that of a safety valve to be kept in reserve rather
than a source of frequent application. Art. 38 (1) (c) describe the
inexhaustible reservoir of legal principles from which the tribunals can enrich
and develop international law.
4. Judicial Decisions and Juristic Works
Art. 38 (1) (d) of the Statute of ICJ
states that the Court shall apply subject to the provisions of Art. 59,
judicial decisions and teachings of the most highly qualified publicists of
various nations, as subsidiary means for the determination of rules of law
Thus, judicial decisions and juristic works are
subsidiary and indirect sources of international law. The decisions of
International Court of Justice do not create a binding general rule of
international law, as Art. 59 of the Statute of ICJ make it clear that the
decisions of the court will have no binding force except between the parties
and in respect of the particular case. Although ICJ has not adopted the common
law doctrine of precedent (i.e. stare decisis), it has largely adopted its
So far as the advisory opinion of the ICJ is concerned, it is not
binding at all. But it clarifies the rule of international law on a particular
point or matter. The decisions of ICJ have enormously influenced States and
codifying agencies. The rule of equitable principles enunciated in North Sea
Continental Shelf Cases was adopted and developed in many cases and also
incorporated in the 1982 U.N. Convention on Law of Sea. In practice, the
decisions of ICJ have assumed such an importance that these constitute a source
of international law and are not merely subsidiary means for determining the
rules of law.
State judicial decisions
It is true that decisions of municipal courts of a State have little value in
international law, but the uniform decisions of the courts of many States have a
tendency to create evidence of international custom especially in those fields
of international law which are interwoven between international law and
municipal law such as nationality, extradition and diplomatic immunities.
Writings of Jurists
This source may be resorted to as final resort i.e. only when all the other
sources listed in Art. 38 have failed to resolve the dispute before the Court.
Sometimes juristic opinion does lead to the formation of international law. Calvo clause
and Drago doctrine
are the instances of such rules in
international law. In Paquete Habana Case,
Justice Gray observed: Where there
is no treaty and no controlling executive or legislative act or judicial
decision, resort must be had to the customs and usages, and, as evidence of
these, to the works and commentators, who by years of labour, research and
experience have made themselves peculiarly well acquainted with the subjects
which they treat.
5. Resolutions of the General Assembly (Modern Sources of International Law)
After the establishment of U.N., most of the development of international law
and its codification has taken place through the instrumentality of
international organizations. General Assembly, one of the principal organs of
U.N., has established International Law Commission. The decisions and
determinations of organs are now recognized as an important source of
international law (although they do not find mention in Art. 38 of the Statute
Resolutions of the General Assembly of the United Nations do not possess legal
character, and as such are not binding on the States. They do not create any
legal obligations on its members irrespective of the fact that they have been
adopted unanimously or by overwhelming votes or even if the contents of it is a
matter of common interest for all the States. A perusal of the cases like South
West Africa Voting Procedure Case (ICJ, Rep. 1955), Anglo-Norwegian Fisheries
Case (ICJ, Rep. 1951), ICJ's Advisory opinion on Namibia and the Western Sahara
Case indicates that legal effect may be given to collective pronouncements of
the General Assembly despite their non-binding character.
Since there is no world government, there is no world Congress or parliament to
make international law the way domestic legislatures create laws for one
country. As such, there can be significant difficulty in establishing exactly
what international law is.
Various sources, however principally treaties between states are considered
authoritative statements of international law. Treaties are the strongest and
most binding type because they represent consensual agreements between the
countries who sign them. At the same time, as stated in the statute of
the International Court of Justice (ICJ), rules of international law can be
found in customary state practice, general principles of law common to many
countries, domestic judicial decisions, and the legal scholarship.