Public International Law: Chapter II — The Sources of International Law (September 19, 2023)

 Chapter II — The Sources of International Law 

What sources are.

Domestics Sphere.

• Domestic laws are found in statute books and in collections of court decisions.

International Law. 

• In the absence of a centralized legislative, executive and judicial structure, there is no single body able to legislate and there is no system of courts with compulsive power to decide what the law is nor is there a centralized repository of international law. 
• There is the problem of finding out where the law is. 
• This problem is exacerbated by the anarchic nature of world affairs and the competing sovereignties. 
• Nevertheless international law exists and there are “sources” where, with some effort, the law can be found.

Classification of Sources:

 1. Formal sources 

• various processes by which rules come into existence
• ex: legislation, treaty making and judicial decision making as well as the practice of states

2. Material sources

• not concerned with how rules come into existence but rather with the substance and content of the obligation 
• they identify what the obligations are
• ex: state practice, UN Resolutions, treaties, judicial decisions and the writings of jurists in so far as they identify what the obligations are.
• they are also sometimes referred to as “evidence” of international law.

Doctrine of Sources 

• lays down conditions for verifying and ascertaining the existence of legal principles
• the conditions are the observable manifestations of the “wills” of States as revealed in the processes by which norms are formed —that is, treaty and state practice accepted as law

Article 38(1) of the Statute of the International Court of Justice

1. The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply: 

a. international conventions, whether general or particular, establishing rules expressly recognized by contesting states; 

b. international custom, as evidence of a general practice accepted as law; 

c. the general principles of law recognized by civilized nations; 

d. 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. 

2. This provision shall not prejudice the power of the Court to decide ex aequo et bono, if the parties agree thereto.

•  the most widely accepted statement of the “sources” of international law
• does not speak of sources
• a directive to the Court on how it should resolve conflicts brought before it
• declaration by states that these are the laws under which they are willing to be bound.

Restatement (Third) of Foreign Relations Law of the United States

1. A rule of international law is one that has been accepted as such by the international community of states 

a) in the form of customary law;

b) by international agreement; or 

c) by derivation from general principles common to the major legal systems of the world.

2. Customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation.

3. International agreements create law for the states parties thereto and may lead to the creation of customary international law which such agreements are intended for adherence by states generally and are in fact widely accepted.

4. General principles common to the major legal systems, even if not incorporated or reflected in customary law or international agreements, may be invoked as supplementary rules of international law where appropriate.

“Sources” of international law are:

1. custom, 
2. treaties and other international agreements, 
3. generally recognized principles of law,
4. judicial decisions and 
5. teachings of highly qualified and recognized publicists

1. Custom or customary law

Custom or customary international law

“a general and consistent practice of states 

followed by them 

from a sense of legal obligation.” (Restatement)

Two basic elements of custom: 

1. the material factor
• how states behave
2. psychological or subjective factor,
• why they behave the way they do

The material factor: practice of states or usus

• the initial factor for determining the existence of custom is the actual behavior of states (usus)
• this includes several elements: 
• Duration
• the required duration (diuturnitas) can be either short or long
• ex: The Paquete Havana  
• on the exemption of fishing vessels from capture as prize of war
• result of long, almost immemorial, practice
• ex: In the North Sea Continental Shelf Case
• a short duration, by itself, will not exclude the possibility of a practice maturing into custom provided that other conditions are satisfied:
• . . . Although the passage of only a short period of time is not necessarily, or of itself, a bar to the formation of a new rule of customary international law on the basis of what was purely a conventional rule, an indispensable requirement would be that within the period in question, short though it might be, 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.
• not the most important element
• more important is the consistency and the generality of the practice
• Consistency
• continuity and repetition
• Ex: Asylum Case (ICJ Reports 1950)
• On October 3rd, 1948, a military rebellion broke out in Peru; it was suppressed the same day. 
• On the following day, a decree was published charging a political party, the American People’s Revolutionary Party, with having prepared and directed the rebellion. 
• The head of the Party, Victor Raul Haya de la Torre, was denounced as being responsible. With other members of the party, he was prosecuted on a charge of military rebellion...
• On January 4th, 1949, the Colombian Ambassador in Lima informed the Peruvian Government of the asylum granted to Haya de la Torre, at the same time he asked that a safe-conduct be issued to enable the refugee to leave the country. 
• On January 14th, he further stated that the refugee had been qualified as a political refugee. 
• The Peruvian Government disputed this qualification and refused to grant a safe-conduct. A diplomatic correspondence ensued which terminated in the signature, in Lima, on August 31st, 1949, of an Act by which the two Governments agreed to submit the case to the International Court of Justice.
• The decision of the ICJ was against Colombia:
• Finally, as regards American international law, Colombia had not proved the existence, either regionally or locally, of a constant and uniform practice of unilateral qualification as a right of the State of refuge and an obligation upon the territorial State. 
• The facts submitted to the Court disclosed too much contradiction and fluctuation to make it possible to discern therein a usage peculiar to Latin America and accepted as law.
• It therefore followed that Colombia, as the State granting asylum, was not competent to qualify the nature of the offence by a unilateral and definitive decision binding on Peru.
• Generality of the Practice of States
• uniformity and generality of practice need not be complete, but it must be substantial
• ex: Nicaragua v. United States (ICJ Reports 1986)
• the practice need not be “in absolute conformity” with the purported customary rule
• In order to deduce the existence of customary rules, the Court deems it sufficient that the conduct of states should, in general, be consistent with such rules, and that instances of state conduct inconsistent with a given rule should generally have been treated as breaches of that rule, not as indications of the recognition of a new rule.

Opinio juris

• once the existence of state practice has been established, it becomes necessary to determine why states behave the way they do

Q: Do states behave the way they do because they consider it obligatory to behave thus or do they do it only as a matter of courtesy? 

Opinio juris, or the belief that a certain form of behavior is obligatory, is what makes practice an international rule. Without it, practice is not law.... Even humanitarian consideration by itself does not constitute opinio juris.

• ex: Nicaragua v. United States (ICJ Reports 1986)
• For a new customary rule to be formed, not only must the acts concerned ‘amount to a settled practice,’ but they must be accompanied by the opinio juris sive necessitatis. Either the States taking such action or other States in a position to react to it, must have behaved so that their conduct is “evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it.” The need for such a belief, i.e., the existence of a subjective element, is implicit in the very notion of the opinio juris sive necessitatis.
• it is also possible for customary law to develop which will bind only several states, or even only two states
• but the party claiming it must prove that it is also binding on the other party
• in the Asylum case, this was not proved
• but this was proved in the case of Right of Passage over Indian Territory (ICJ Reports 1960)
• the right of Portugal to pass through Indian territory was recognized

Dissenting states; subsequent contrary practice

Q: Would dissenting states be bound by custom? 

Yes, unless they had consistently objected to it while the custom was merely in the process of formation. 

• The authority that is usually used for this is the Anglo-Norwegian Fisheries* case 
• the ICJ said that a coastline delimitation rule put forward by England “would appear to be inapplicable as against Norway, in as much as she has always opposed any attempt to apply it to the Norwegian coast.” 
• dissent, however, protects only the dissenter and does not apply to other states
• a state joining the international law system for the first time after a practice has become law is bound by such practice

Q: It is also possible that after a practice has been accepted as law, contrary practice might arise. What effect would such contrary practice have?

In Fisheries Jurisdiction Case (Merits) the opinion was expressed that such contrary practice can cast doubt on the alleged law. It noted “great uncertainty as to the existing  customary law on account of the conflicting and discordant practice of States.” It concluded that the uncertainty had “an unsettling effect on the crystallization of a still evolving customary law on the subject.” ... It might be added that, over time, if the contrary practice should gain general acceptance, it might instead become the law.

Evidence of state practice and opinio juris

Q: What are the acceptable evidence of state practice? 

Various forms of evidence may point to state practice. These can be treaties, diplomatic correspondence, statements of national leaders and political advisers, as well as the conduct of states. By themselves, however, they do not constitute customary law unless characterized by opinio juris. The existence of opinio juris is a matter of proof. The burden of proving its existence falls on the state claiming it. 

Nicaragua v. United States

• one of the issues was whether the prohibition of the use of force was customary law
• It considers that this opinio juris may be deduced from, inter alia, the attitude of the Parties and of States towards certain General Assembly resolutions, and particularly Resolution 2625 (XXV) entitled “Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in Accordance with the Charter of the United Nations.” Consent to such resolutions is one of the forms of expression of an opinio juris with regard to the principle of non-use of force, regarded as a principle of customary international law, independently of the provisions, especially those of an institutional kind, to which it is subject on the treaty-law plane of the Charter.

“Instant custom”

Q: Is there such a thing as “instant custom?”

What is referred to as “instant custom” is not the product of constant and prolonged practice. 

Rather it comes about as a spontaneous activity of a great number of states supporting a specific line of action. 

• in the after- math of the attack on the Word Trade Center in New York, a coalition of forces arose in a matter of months supportive of the action taken by the United States against Osama Bin Laden
• this united action may have given birth to instant customary law classifying the attack as an armed attack under Article 51 of the UN Charter justifying collective self-defense
• what was peculiar about this collective action was that the object of defense was not an attack from a state but from a non-state organization

Usus and opinio juris in Humanitarian Law: The Martens Clause

• the Martens Clause refers to a paragraph found in the 1899 Hague Peace Convention

Until a more complete code of laws of war has been issued, the High Contracting parties deem it expedient to declare that, in cases not included in the Regulations adopted by them, the inhabitants and belligerents remain under the protection and the rule of the principles of the law of nations as they result from the usages established among civilized peoples, from the laws of humanity, and the dictates of the public conscience.

• first inserted by the Russian publicist Fyodor Martens and has found its way into a number of treaties including the:
• 1949 Vienna Convention
• First Additional Protocol of 1977
• it has been cited by, among others, the ICJ in the Legality of the Threat or Use of Nuclear Weapons
• the clause puts the “laws of humanity” and the “dictates of public conscience” on the same level as “usages of states” or usus thus suggesting that even without practice or usus or at least without consistent practice there can emerge a principle of law based on laws of humanity and the dictates of public conscience
• in other words, one need not wait for thousands of civilians to be killed before a ban becomes effective
• it fills in any gaps in the Hague Convention and provides a general rule of protection for persons affected by armed conflict; it is also important because it affirms the role of natural law in international humanitarian law

2. Treaties.

•  another important source are treaties or international agreements, whether bilateral or multilateral. 
• it determine the rights and duties of states just as individual rights are determined by contracts
• their binding force comes from the voluntary decision of sovereign states to obligate themselves to a mode of behavior
• while treaties are generally binding only on the parties, the number of the contracting parties and the generality of the acceptance of the rules created by the treaty can have the effect of creating a universal law in much the same way that general practice suffices to create customary law

Q: Are treaties law or merely obligations which the law says must be carried out?

On the basis of this question, a distinction is made between “contract treaties” or “law making treaties.” The distinction, perhaps, is not very useful because all treaties must be observed by the parties under the principle of pacta sunt servanda.

Treaties and custom

• whether or not treaties override custom depends on the intention of the parties
• if the treaty is intended to be declaratory of customary law, it may be seen as evidence of customary law
• normally, treaties and custom can be complementary
• Nicaragua v. United States
• adherence to treaties can be indicative also of adherence to practice as opinio juris. 

Q: What happens, however, when treaty and custom contradict each other? 

Different situations may have different solutions.

1. If a treaty comes later than a particular custom, as between the parties to the treaty, the treaty should prevail. A treaty manifests a deliberate choice of the parties and the principle of pacta sunt servanda should be followed. 

• Wimbledon Case (PCIJ 1923)
• although the PCIJ recognized that customary international law prohibited belligerents from ferrying armaments through a neutral state, the Court said that Article 380 of the Treaty of Versailles opened the Kiel Canal to passage “to the vessels of commerce and of war of all nations at peace with Germany on terms of entire equality.”
• the Kiel Canal cut through Germany linking the Baltic and North Sea
• The Court considers that the terms of Article 380 are categorical and give rise to no doubt. It follows that the canal has ceased to be an internal and national navigable waterway, the use of which by the vessels of states other than the riparian state is left entirely to the discretion of that state, and that it has become an international waterway intended to provide under treaty guarantee easier access to the Baltic for the benefit of all nations of the word...

2. However, if a later treaty is contrary to a customary rule that has the status of jus cogens, custom will prevail. 

• Article 53 of the Vienna Convention on the law of Treaties:
• A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. For the purposes of the present Convention, a peremptory norm of general international law is a norm accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.

3. In a situation, where custom develops after a treaty, the rule is not clear. 

The logical rule perhaps should be that the later custom, being the expression of a later will, should prevail.

• but such an approach would militate against the certainty of treaties
• in practice, however, an attempt is made to keep the treaty alive by efforts at reconciling a treaty with the developing custom
• ex: Anglo-French Continental Shelf Case (1979). 
• the issue was the applicability of the equidistance principle in the delimitation of the continental shelves of the United Kingdom and France
• Article 6 ... does not formulate the equidistance principle and “special circumstances” as two separate rules. The rule there stated in each of the two cases is a single one, a combined equidis- tance-special circumstances rule. ... The Court does not overlook that under Article 6 the equi-distance principle ultimately possesses an obligatory force which it does not have in the same measure under the rules of customary law, for Article 6 makes the application of the equidistance principle a matter of treaty obligation for Parties to the Convention. But the combined character of the equidistance-special circumstances rule means that the obligation to apply the equidistance principle is always one qualified by the condition “unless another boundary line is justified by special circumstances. ...”

3. General principles of law recognized by civilized nations. 

• this is also referred to by the Restatement as “general principles of law recognized by or common to the world’s major legal systems.” 
• this has reference not to principles of international law but to principles of municipal law common to the legal systems of the world
• they may, in a sense, be said to belong to no particular system of law but are evidence rather of the fundamental unity of law
• most of these principles, however, have either become part of customary law or have been incorporated into conventional international law. 
• the Restatement avoids the language “civilized nations.”
• its colonial connotation is now unacceptable in the international community
• the Restatement refers to them as “supplementary rules of international law.” 
• these may be found in “judicial decisions and the teachings of the most highly qualified publicists of the various nations” which the Statute refers to as “subsidiary means for the determination of rules of law.” 
• ex: 1928 Chorzow Factory case 
• the Permanent Court declared that “it is a general conception of law that every violation of an engagement involves an obligation to make reparation.” 
• ex: the affirmation that private rights acquired under one regime does not cease upon the change of government
• ex: principle of estoppel 
• the affirmation of general principles of law found in domestic systems as a source of international law makes up for the fact that there is no international legislative system. 
• the insertion of this provision in Article 38(1) thus plugs some of the gaps in the existing international law system
• Barcelona Traction Case (ICJ 1964) 
• adverted to this purpose
• If the Court were to decide the case in disregard of the relevant institutions of municipal law, it would without justification, invite serious legal difficulties. It would lose touch with reality.... It is to rules generally accepted by municipal systems,... and not to the municipal law of a particular State, that international law refers.

4. Judicial decisions.

• Article 38 of the Statute directs the Court to apply judicial decisions as subsidiary means for the determination of the rules of law. 
• but this is made subject to Article 59 which says that “the decisions of the court have no binding force except between the parties and in respect of that particular case.
• hence, such decisions do not constitute stare decisis
• however, the decisions of the ICJ are not only regarded as highly persuasive in international law circles; they have also contributed to the formulation of principles that have become international law
• the ICJ is the source of principles recognizing the international personality of international organizations
• the doctrine on “genuine link” between a person and a state for purposes of jurisdiction
• the straight baseline method in drawing baselines for archipelagos 
• similarly, arbitral decisions have been instrumental on the formation of international law principles

5. The teachings of highly qualified writers and “Publicists.”

• in many cases of first impression, the only authorities that can be cited are writers
• the extent to which they are referred to depends on the tradition of the court or of individual judges.
• in common law jurisdictions, there is reluctance to use them, more so in the US than in Britain
• in civil law jurisdictions, there is more ready reference to writers
• the ICJ is generally reluctant to refer to writers but they are often taken into consideration

“Publicists”

• institutions which write on international law
• they also play a role, the more significant ones are:
• The International Law Commission, an organ of the U.N.; 
• Institut de Droit International, the International Law Association, a multinational body;
• (Revised) Restatement of Foreign Relations Law of the United States; 
• Hague Academy of International Law annual publication
• however, that these institutions are generally government sponsored; hence, they bear within themselves a potential for national bias

6. Equity.

• Diversion of Water from the Meuse (Netherlands v. Belgium)
• the Permanent Court of Justice had occasion to use equity as a source of law
• Netherlands had complained that certain canals constructed by Belgium were in violation of an agreement in that the construction would alter the water level and rate of flow of the Meuse River. The Court rejected the Netherlands claim and a Belgian counterclaim based on the construction of a lock by the Netherlands at an earlier time. 
• Judge Hudson Concurring Opinion:
• It would seem to be an important principle of equity that where two parties have assumed an identical or a reciprocal obligation, one party which is engaged in a continuing non-performance of that obligation should not be permitted to take advantage of a similar no-performance of that obligation by the other party. The principle finds expression in the so-called maxims of equity which exercised great influence in the creative period of the development of the Anglo-American law. Some of these maxims are, “Equality is equity”; “He who seeks equity must do equity.” It is in line with such maxims that “a court of equity refuses relief to a plaintiff whose conduct in regard to the subject-matter of the litigation has been improper.” A very similar principle was received into Roman Law. The obligations of a vendor and a vendee being concurrent, “neither could compel the other to perform unless he had done, or tendered, his own part.” 
• The Court has not been expressly authorized by its Statute to apply equity as distinguished from law. Nor, indeed, does the Statute expressly direct its application of international law, though as has been said on several occasions the Court is “a tribunal of international law.” Article 38 of the Statute expressly directs the application of “general principles of law recognized by civilized nations,” and in more than one nation principles of equity have an established place in the legal system. The Court’s recognition of equity as a part of international law is in no way restricted by the special power conferred upon it “to decide a case ex aequo et bono, if the parties agree thereto.” It must be concluded, therefore, that under Article 38 of the Statute, if not independently of that Article, the Court has some freedom to consider principles of equity as part of the international law which it must apply.
• equity, when accepted, is an instrument whereby conventional or customary law may be supplemented or modified in order to achieve justice.
• it has both a procedural and substantive aspect:
• procedurally:
• a mandate given to a judge to exercise discretion in order to achieve a determination that is more equitable and fair. 
• different kinds of equity are distinguished: 
• intra legem (within the law), that is, the law is adapted to the facts of the case;
• praeter legem (beyond the law), that is, it is used to fill the gaps within the law;
• and contra legem (against the law), that is, a refusal to apply the law which is seen as unjust
• ex aequo et bono
• "according to what is fair and equitable"

7. Other supplementary evidence.

UN Resolutions

• Declarations of legal principles and Resolutions by the United Nations are generally considered merely recommendatory
• but if they are supported by all the states, they are an expression of opinio juris communis
• but a growing number of weaker nations, who have a very substantial vote, feel that U.N. Resolutions should have the force of law
• Resolutions can also be a reflection of what has become customary law

“Soft Law”

• not included among the sources is what a growing literature refers to as “soft law” 
• others prefer to call this category “non-treaty agreements”  
• international agreements not concluded as treaties and therefore not covered by the Vienna Convention on the Law of Treaties
• other sources of soft law are administrative rules which guide the practice of states in relation to international organizations. 
• these are mostly administrative procedures that are carried out with varying degrees of consistency and uniformity that may eventually ripen into customary law or become formalized later on in treaties
• soft law plays an important role in international relations because often states prefer non-treaty obligations as a simpler and more flexible foundation for their future relations.
• the difference lies mainly in the wish of the parties to model their relationship in a way that excludes the application of treaty or customary law on the consequences of a breach of obligations