SOURCES OF

INTERNATIONAL LAW:

A RE-EVALUATION

By

ABDUL GHAFUR HAMID @ KHIN MAUNG SEIN

Associate Professor

Ahmad Ibrahim Kulliyyah of Laws

International Islamic University Malaysia

IIUM Law Journal

Vol. 11, No. 2 (2003) 203-240

2

SOURCES OF INTERNATIONAL LAW:

A RE-EVALUATION

ABDUL GHAFUR HAMID @ KHIN MAUNG SEIN

1

ABSTRACT

The changes in international community since 1945 have led to fundamental

disputes on the sources of international law and it must be admitted that they have

become an area of considerable4 theoretical controversy. In particular, the two

traditional sources, custom and treaty, are now often difficult to distinguish clearly.

The present paper attempts to clearly identify the interaction between the two main sources, namely customary law and treaty law, and clarify the controversy relating

to the hierarchy among the sources of international law. The writer finds that

custom and treaties are still the primary sources of international law and that there is no hierarchy between them: they are of equal status. In recent years, however, a new

category of international rules, jus cogens, has come into being, which is

hierarchically superior to all the other rules of international law. The writer suggests

that between treaty law and customary law, the practice is that if there is a treaty

binding the two parties to a dispute, the Court will, first of all, look at the treaty,

which is a jus scriptum. Even in such a situation, however, we cannot say that

customary law is entirely irrelevant. The Court in most cases applies both treaty law

and customary law simultaneously so that it can deal with all the legal issues

involved in the dispute. If there is no treaty binding the two parties to a dispute, then the Court has to rely exclusively on customary international law for the

determination of the dispute. If no relevant rule can be found in treaty law and

custom, then the court may apply the general principles of law. The other sources are merely secondary or material sources and most of them can be used as evidence

of customary law.

1. INTRODUCTION

In every legal system there must be some criteria by which legal norms or ‘laws’ are

recognized. It must have reasonably clear ‘sources of law’. Generally speaking, these

sources of law are either ‘law creating’ or ‘law identifying’. That is why writers

usually distinguish the ‘formal sources’ and the ‘material sources’ of law.2 According

to Salmond, “A formal source is that from which a rule of law derives its force and

validity…. The material sources, on the other hand, are those from which is derived

the matter, not the validity, of the law. The material source supplies the substance of

the rule to which the formal source gives the force and nature of law”. 3 Simply put, a

1 LL.M. (Yangon), Ph.D. (IIUM), Associate Professor, Ahmad Ibrahim Kulliyyah of Laws,

International Islamic University Malaysia. I am greatly indebted to the Research Centre, International

Islamic University Malaysia, for funding this research. 2 See, Brownlie, Ian, Principles of Public International Law, 5th.ed., 1998, 1; Schwarzenberger,

Georg, International Law, vol. 1, 3rd.ed., 1957, 26-27; Hart, H.L.A., The Concept of Law, 1961, 246-7.

However, Professor Brownlie is of the following view: In the context of international relations, the use

of the term ‘formal source’ is misleading because there is no constitutional machinery of law-making in

the creation of rules of international law. Brownlie, op. cit., 2. 3 Salmond, J.W., Jurisprudence, 7th.ed., 1924, para. 24.

3

formal source represents the mechanism through which the law comes into being,

whereas a material source indicates where the legal rules come from, that is, where

the rules are located. In other words, the function of a formal source is ‘law creating’

whereas the function of a material source is ‘law identifying’.

Where do international lawyers look to find international law? There are, in the

context of international law, recognized and accepted methods by which legal rules

come into existence (formal sources) as well as several ways in which the precise

content of legal rules can be identified (material sources)4. These are the sources of

international law.

The most important source of international law for centuries was customary law,

evolving from the practice of States.5 The recent attempts to codify international law

and the conclusion of multilateral treaties in many important areas have sought to

clarify the law and to establish universally accepted norms. But customary law has

still retained its predominance over treaty law or other sources in many other areas,

such as, for example, State immunity or State responsibility. The changes in

international community since 1945 have led to fundamental disputes on the sources

of international law and it must be admitted that they have become an area of

considerable theoretical controversy. In particular, the two main traditional sources,

custom and treaty, are now often difficult to distinguish clearly.6 The main objectives

of the present paper, therefore, are to clearly identify the interaction between the two

main sources, namely customary law and treaty law, and to clarify the controversy

relating to the hierarchy among the sources of international law.

2 STATUTE OF THE INTERNATIONAL COURT OF JUSTICE

Article 38 of the Statute of the International Court of Justice is always the starting

point for any study of the sources of international law.

Article 38

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

recognized by the 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 the rule of law.

2. This provision shall not prejudice the power of the Court to decide a case ex aequo

et bono, if the parties agree thereto.

4 For example, a rule will be legally binding if it meets the requirements of a custom, which is a

formal source of international law, and its substance will be indicated by State practice, which is the

material source of custom. The term evidence is then used in the sense that diplomatic correspondence,

for example, is evidence of State practice. 5 See Bernhardt, R., “Customary International Law”, (1995) 11 Encyclopaedia of Public

International Law (EPIL), 1255-62. 6 As Jennings put it in 1981: “I doubt whether anybody is going to dissent from the proposition that

there has never been a time when there has been so much confusion and doubt about the tests of the

validity – or sources – of international law, than the present”. See Jennings, R., “What is International

Law and How Do We Tell When We See It?” (1981) 37 ASDI, 59-88.

4

These provisions are expressed in terms of the function of the Court, but they

represent the previous practice of arbitral tribunals, and are generally regarded as an

authoritative statement of the sources of international law.7 Some writers have

criticized the Article on the ground that it does not list all the sources of international

law, or that it includes aspects which are not genuine sources, but none of the

alternative lists which have been suggested has won general approval.8 It is therefore

proposed to examine the sources listed in the Court’s Statute before considering other

possible sources of international law.

3 TREATIES

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

to apply “international conventions, whether general or particular, establishing rules

expressly recognized by the contesting States”. The word ‘convention’ means a treaty

and whatever the nomenclature is9, the substance is the same: it is an agreement made

between two or more States or other subjects of international law.

3. 1 Treaty as a source of international law

A treaty is based on consent. Such consent may be expressed by one of the accepted

methods (signature, ratification, accession, etc.). Once a treaty has entered into force,

it is binding on the parties to it. By virtue of the maxim pacta sunt servanda, States

parties shall perform the treaty in good faith. In other words, the treaty is the law for

the parties. Failure to comply with the terms of a binding treaty will incur

international responsibility unless a defence is available.10

Being based on consent, the general principle is that only the parties to a treaty are

bound by its terms. As the Permanent Court of International Justice in 1926 put it in

Certain German Interests in Polish Upper Silesia, “a treaty only creates law as

between the States which are parties to it’11

. Hence, for third States treaties are

something devoid of any legal consequence: they are a thing made by others (res inter

alios acta). To put it differently, a treaty may not impose obligations or confer rights

on a third party. This is often expressed in terms of the Latin maxim pacta tertiis nec

nocent nec prosunt. This general principle is now stated in Article 34 of the Vienna

Convention on the Law of Treaties, 1969, which reads: “A treaty does not create

either obligations or rights for a third State without its consent”.12

7 Akehurst’s Modern Introduction to International Law, 7

th. Revised Ed., 1997, 36. Brownlie,

Principles of Public International Law, 5th.ed., 1998, 3.

8 The International Court of Justice has been prepared to consider other sources not listed in Article

38. On the practice of the Court, see Mendelson, M., “The International Court of Justice and the

Sources of International Law”, in Lowe, V., and Fitzmaurice, M., (eds.) Fifty Years of the International

Court of Justice, 1996, 63-89. 9 International agreements may have various names: treaties, conventions, protocols, pacts,

covenants, statutes, final acts, and so on. 10

Case Concerning Gabcikovo – Nagymaros Project (Hungary v Slovakia) (1998) 37 ILM 162

(Danube Dam Case). 11 Certain German Interests in Polish Upper Silesia, (1926) PCIJ Series A. no. 7. at 29. 12

There are a number of exceptions to this general rule:

(1) It is recognized that there is a distinct category of ‘dispositive treaties’ that create an

objective legal regime binding upon third States. See Case Concerning Kasikili/Sedudu

Island (Boswana v Namibia), ICJ Judgment of 13 December 1999. For s discussion see

5

Law-making treaties and treaty-contracts

Some writers have tried to argue that treaties should be regarded as sources of

international law only if they resemble domestic law statutes in content; that is to say,

only if they are the so-called ‘law-making treaties’. A law-making treaty has been

defined as a treaty concluded by a substantial number of States and stipulates new

general rules for future international conduct or abolishes, modifies or codifies

existing customary or conventional rules of a general character.13

According to this

theory, the so-called ‘treaty-contracts’, on the other hand, are treaties between two or

only a few States, dealing with a special matter concerning these States exclusively.

These treaties (for instance, a treaty whereby one State agrees to lend a certain sum of

money to another State) resemble contracts in domestic law and are not a source of

international law but are merely legal transactions.

We cannot accept such an idea. It is too vague and imprecise to justify regarding law-

making treaties as the only treaties, which are a source of international law. The so-

called treaty-contracts may, as between the parties thereto, constitute particular law.

That is why the expression ‘general or particular conventions’ is used in Article 38(1)

of the Statute. Moreover, even bilateral treaties may provide evidence of customary

rules.14

The better view, therefore, is to regard all treaties as a source of law.15

3. 2 Interaction between treaty law and customary law

Customary international law derives from the practice of States. It is by nature slow in

its law-making process. There is lack of precision in customary rules, and it is very

often quite difficult to ascertain their exact contents. On the other hand, treaty-making

process is relatively faster. States may enter into a treaty at any time when they feel

that a new rule is required. Treaties are the only way by which international law can

be made by a deliberate act of States. In this way treaties are contributing to the rapid

expansion of international law.16

Since treaty law is a kind of written law (jus

scriptum), it possesses the merit of considerable precision. It is not surprising,

therefore, that treaties are fast becoming the most important source of international

law.

Treaty as a material source of customary law

North Sea Continental Shelf cases17

are concerned with the role of multilateral treaties

as State practice and hence as a material source of customary international law

Shaw, Malcolm, (2000) 49 ICLQ 964.

(2) A multilateral treaty declaratory of existing customary international law will have effect

upon non-parties; however, in this instance, the non-party is bound not by the treaty but by

the customary rule. See, O’Brien, John, International Law, Cavendish Publishing Ltd.,

London, 2001, 331. 13

See, McNair, The Law of Treaties, Clarendon Press, Oxford, 1961, 5, 124. 14

Brownlie, Principles of Public International Law, 5th.ed., 1998, 13.

15 Akehurst’s Modern Introduction to International Law, 7th.ed., 1997, 38. 16

One of the most significant changes in international law has been the growth in the volume of

treaties. The evidence can be seen in the United Nations Treaty Series. Since 1945 over 30,000 treaties

have been registered with the United Nations. 17 (1969) ICJ Rep. 3.

6

binding upon parties and non-parties alike. In the Court’s view, a treaty rule may

relate to custom in one of three ways:

(1) It may be declaratory of custom at the time when the provision is adopted18

(that

is, it may codify a pre-existing rule of customary international law);

(2) It may crytallise custom, as States agree on the provision to be adopted during the

treaty drafting process;

(3) it may serve to generate a rule of customary international law in the future by

subsequent practice of States).

When a treaty codifies existing customary law, as was the case with much of the

Vienna Convention on Diplomatic Relations, 1961, the substance of the obligations

specified in the treaty may be binding on all States, because: (1) those States that are

parties are bound by the obligations in the normal way since they are parties; and (2)

States that are not parties are also bound by the obligations because they are rooted in

customary law. The substance of the obligation is the same for parties and non-parties,

even though the origin of that obligation is different.

Many multilateral treaties are a mixture of codification of current customary law and

progressive development of that law. In that case, parties to the treaty are bound in the

normal way by all of the obligations in the treaty, but non-parties are bound by those

obligations, which have in fact attained the status of customary law. Furthermore, the

fact that the treaty is intended to lay down a code of conduct for all States in the future

may mean that such a treaty may serve to generate rules of customary law, similar to

those found in the treaty, in the future. If this happens, non-parties will be bound by

the new customary law.

Parallel existence of treaty law and customary law

The question before the Court in the Nicaragua case was whether customary rules on

the use of force and intervention continued to bind the parties in parallel with the

obligations under the UN Charter, so that the Court could apply them despite the US’s

multilateral treaty reservation. Holding that they did, the Court stated:

177…[T]he existence of identical rules in international treaty law

and customary law has been clearly recognized by the Court in the

North Sea Continental Shelf cases. To a large extent, those cases

turned on the question whether a rule enshrined in a treaty also

existed as a customary rule, either because the treaty had merely

codified the custom, or caused it to “crystallise”, or because it had

influenced its subsequent adoption….more generally, there are no

ground for holding that when customary international law is

comprised of rules identical to those of treaty law, the latter

“supervene” the former so that the customary international law has

no further existence of its own.

18

The Preamble to the Convention on the High Seas, 1958, states that it is “generally declaratory of

established principles of international law”.

7

4. INTERNATIONAL CUSTOM

The second source of international law listed in the Statute of the International Court

of Justice is ‘international custom’19

. Article 38 (1)(b) refers to “international custom,

as evidence of a general practice accepted as law”.20

As confirmed by the

International Court of Justice in the Nicaragua case21

, international custom is

constituted by two elements: (1) the objective one of ‘a general practice’; and (2) the

subjective one ‘accepted as law’, the so-called opinio juris. In the Continental Shelf

(Libya v Malta) case22

, the Court stated that the ‘substance of customary international

law must be looked for primarily in the actual practice and opinio juris of States’.

This is the established doctrine, accepted by States, international tribunals and most

writers alike.

4.1 State Practice

The formation of a customary rule requires a general and consistent State practice.

Then what acts constitute State practice? Generally speaking, the actual words and

actions and omissions of States constitute State practice.

4.1.1 Meaning of State practice: What States do and what States say

It is sometimes suggested that State practice consists only of what States do, not of

what they say. For instance, in his dissenting opinion in the Fisheries case, Judge

Read argued that claims made to areas of the sea by a State could not create a

customary rule unless such claims were enforced against foreign ships.23

But in the

later Fisheries Jurisdiction case ten of the fourteen judges inferred the existence of

customary rules from such claims, without considering whether they had been

enforced.24

The better view therefore appears to be that State practice consists not

only of what States do, but also of what they say.

State practice also includes omissions; many rules of international law forbid States to

do certain acts.25

Even silence on the part of States is relevant because passiveness

and inaction with respect to claims of other States can produce a binding effect

creating legal obligations for the silent State under the doctrine of ‘acquiescence’.26

19

Although occasionally the terms are used interchangeably, ‘custom’ and ‘usage’ have different

meanings. A usage is a general practice, which does not reflect a legal obligation, and examples are

ceremonial salutes at sea and the practice of exempting diplomatic vehicles from parking prohibitions. 20 On international custom generally see, Akehurst, M., “Custom as a Source of International Law”,

(1974-75) 47 BYIL 1; Danilenko, G.M., “The Theory of International Customary Law” (1988) 31 GYIL

9; Kirchner, J., “Thoughts about the Methodology of Customary International Law”, (1992) 43 AJPIL,

215-39; Wolfke, K., “Some Persistent Controversies regarding Customary International Law” (1993)

24 NYIL, 1-16; Meron, “The Continuing Role of Custom in the Formation of International

Humanitarian Law”, (1996) 90 AJIL, 238-49. 21

Military and Paramilitary Activities in and against Nicaragua (Nicaragua v US), (1986) ICJ Rep.

14 at 97. 22 Continental Shelf (Libya v Malta) case, (1985) ICJ Rep. 29. 23

Anglo-Norwegian Fisheries case, (1951) IC J Rep. 116, at 191. 24

Fisheries Jurisdiction case (United Kingdom v Iceland) (1974) IC J Rep. 3, at 47 25

Article 2, The ILC’s Draft Articles on the Responsibility of States, 2001. 26 Akehurst’s Modern Introduction to International Law, 7th.ed., 1997, 43.

8

4.1.2 Where to look for evidence of State practice; what are the material sources

of custom?

The material sources of custom or evidence of State practice can be found in the

following27

:

(1) Treaties28

;

(2) Judicial decisions29

;

(3) National legislation30

;

(4)Diplomatic correspondence31

;

(5) Opinions of national legal advisors;

(6) Resolutions relating to legal questions of the General Assembly

(7) Practice of international organizations.

Evidence of customary law may also be found in the writings of international lawyers,

and in judgments of national and international tribunals, which are mentioned as

subsidiary means for the determination of rules of law in Article 38(1)(d) of the

Statute of the International Court of Justice.

3.1.3 Generality of practice

Article 38(1)(b) talks about the ‘general practice accepted as law’.32

Therefore,

generality of practice is a requisite in the formation of customary law. In order for a

‘general custom’ (a rule of general customary international law) to develop (as

opposed to a ‘local custom’ binding only a few States), the practice must be fairly

general. The element of ‘general practice’ refers to the number of States which have

to contribute, actively or passively, towards the customary rule. The term ‘general’

would indicate that common and widespread practice among a significant number of

States is required. While universal practice is not necessary, practice should be

“representative”, at least of all major political and socio-economic systems. Again, the

27

The International Law Commission has suggested a non-exhaustive list of the forms that State

practice may take, Yearbook of the ILC, 1950, vol. II, 368-72. The present list is mainly based on the

list of the ILC. See also Brownlie, Principles of Public International Law, 5th.ed., 1998, 5.

28

Treaties, being the most easily accessible documents to objective analysis as a manifestation of

conduct and of the view of the contracting parties, belong to the most important evidence of customary

law. See Wolfke, K., Custom in Present International Law, 2nd

. rev. ed., Martinus Nijhoff Publishers,

Dordrecht, 1993, 141. 29

Decisions of the ICJ are of decisive importance as evidence of customary rules. Even decisions of

national courts can help develop certain area of international law. Similar decisions of national courts

from a substantial number of States may be an evidence of international custom. 30 The term ‘legislation’ is here employed in a comprehensive sense: it embraces the constitutions of

States, the enactments of their legislative organs,and the regulations and declarations promulgated by

executive and administrative bodies. Obviously they serve as an important store-house of evidence of

State practice. 31 The diplomatic correspondence between Governments must supply abundant evidence of customary

international law . See Yearbook of the ILC, 1950, vol.2, 371. 32

‘General practice’ as mentioned in Article 38(1)(b) stands in contrast to Article 38(1)(a) which

specks of “conventions….recognised by the contesting States”. In the Fisheries case, the Court stated

that: “Although the ten-mile rule has been adopted by certain States both in their national law and in

their treaties and conventions, and although certain arbitral decisions have applied it as between these

States, other States have adopted a different limit. Consequently, the ten-mile rule has not acquired the

authority of a general rule of law”. Anglo-Norwegian Fisheries case (UK v Norway) (1951) ICJ Rep.

131

9

degree of generality required will vary with the subject matter, so that an onerous

customary law obligation may require a more general practice.

Two implications of the generality of practice may be noted. First, the requirement of

general practice (together with opinio juris) appears to be an essential prerequisite for

a ‘general customary rule’, which is to be binding erga omnes. The International

Court of Justice made this point quite clear in the North Sea Continental Shelf cases:

“Customary law rules and obligations,…by their very nature, must have equal force

for all members of the international community.”33

Secondly, generality of practice

both entails and ensures that only one general customary norm emerges on one issue,

The available practice on the matter will have to be so widespread that any remaining

inconsistent practice will be marginal and without direct legal effect. If State practice

is substantially divided and conforms to two or more differing solutions on one issue,

it is not sufficiently widespread and cannot amount to a general customary rule; of

course, a number of local, regional, or special customs may arise, each regulating the

same question in a different manner for different groups of States.

The concept of the generality of practice is subject to important qualifications inherent

in the nature of customary law.

(a) The practice of ‘specially affected’ States

In assessing whether a customary rule has come into existence, State practice must

include the practice of those States whose interests are ‘specially affected’ by the

subject matter of the rule.34

For example, the practice of major maritime powers will

have more significance in the formation of rules on the law of the sea than, for

example, that of a landlocked State. It is not that some States are necessarily more

‘important’ or more powerful than others; it is rather that some States will be directly

affected by certain rules and thus their practice is more significant.

(b) The effect of acquiescence in the formation of international custom

At a time when a particular practice is developing that may crystallize into a rule of

customary international law, a State may react in three possible ways: (i) by doing

nothing (that is, complete silence or acquiescence); (ii) by objecting to the practice

from the outset (that is, the persistent objector); or (iii) by objecting at a later date

when the rule has already established as a custom (that is, the subsequent objector).

It would seem that where there has been a widespread and consistent State practice,

then silence by others may be interpreted as ‘acquiescence’ in the development of a

rule of customary international law. In such a case acceptance of the rule is

established by ‘acquiescence’, It is argued that the effect of the wording of Article

38(1)(b) is to create a presumption that all States whether or not they have

participated in the practice are presumed to have assented to the rule unless they can

demonstrate that they have the status of a persistent objector.35

Therefore, it is not

33 North Sea Continental Shelf cases, (1969) ICJ Rep. 38, para 63. 34

North Sea Continental Shelf cases, (1969) ICJ Rep., 3, at para 73: “…a very widespread and

representative participation in the (1958 Continental Shelf) Convention might suffice of itself, provided

it included that of States whose interests were specially affected”, and para. 74. 35 O’Brien, John, International Law, Cavendish Publishing Ltd., London, 2001, 76.

10

surprising that once a rule of general customary international law has been

established, the rule is binding upon the international community as a whole36

, that is,

all States (with the exception of a persistent objector State).

(c) The practice of dissenting States

Not all active practice will adhere to a customary rule. States may wish to dissent

from such rule. They can do so expressly in their statements or votes37

or by means of

protests,38

or impliedly (in the case of positive conduct) by abstaining from practice or

adhering to a different practice. Reservations to a treaty may also represent dissent.

The Persistent objector

As a general rule39

, no international obligation may be placed on a State without that

State’s consent40

; this is inherent in the notion of sovereignty. Again, a distinctive

feature of customary international law is that since a State practice does not need to

receive universal acceptance to be considered a rule of customary law, a State is

unable by its own objection to prevent a customary law from coming into existence.

A State, nevertheless, may contract out of a custom in the process of formation. When

a State object to a particular practice carried on by other States or adopts a contrary

practice, it may not be bound by any evolving customary law. This is known as the

concept of ‘persistent objector’.41

A persistently objecting State is not bound by the

eventual customary rule if the State fulfils two conditions. First, the objections must

have been maintained from the early stages of the rule onwards, up to its formation,

and beyond. Secondly, the objections must be maintained consistently.42

Evidence of

objection must be clear and there is probably a presumption of acceptance, which is to

be rebutted. Whatever the theoretical underpinnings of the principle43

, the concept

36

Harris, D.J., Cases and Materials on International Law, 5th.ed., 1998, 25, n. 1.

37 They played an important part in the Texaco v Libya Arbitration, (1979) 53 ILR 486.

38 MacGibbon, “Some Observations on the Part of Protest in International Law”, (1953) BYIL 310.

39 The only exception is the concept of ‘jus cogens’. That is why it has been argued that a persistent

objector cannot escape being bound by a new rule of customary international law that has the character

of jus cogens. See, e.g., Henkin, Louis, International Law: Politics and Values, 1995, 39. 40

This is based on the ‘consensual theory’ of international law. In its pure form, this consensual

theory or positivist theory stipulates that no international law can be created without the consent of the

State, which is to be bound. This theory recognises that a State’s consent may be given in a variety of

ways – express in treaties or implied in custom – but essentially the system of international law is based

on voluntary self-restriction. 41 Colson, David, “How Persistent Must the Persistent Objector Be?” (1986) 61 Washington L. Rev.

957; Stein, T.L., “The Approach of the Different Drummer: The Principle of the Persistent Objector in

International Law”, (1985) Harvard JIL, vol. 26, No. 2, 457-482. 42

Villiger, Customary International Law and Treaties, Martinus Nijhoff Publishers, Dordrecht,

1985, 14. 43

Charney is of the view that the persistent objector rule has no legitimate basis in international

legal system; see Charney, J., “The persistent Objector Rule and the Development of Customary

international Law”, (1985) 56 BYIL 1. Charney argues: “The rule has attracted the interest of writers

even though it is rarely invoked in practice. For the latter reason, among others, the rule is open to

serious doubt….The International Court has referred to the persistent objector rule in two judgments

(Fisheries case and Asylum case), but only as dicta, and decided the cases on other grounds. Thus

State practice and other evidence do not support the existence of the persistent objector rule”; see

Charney, J., “Universal International Law”, (1993) 87 AJIL 529, at 538-39.

11

appears to have been accepted by overwhelming majority of writers44

and in the

practice of States.45

The authority that writers primarily rely upon to support this rule

is the Anglo-Norwegian Fisheries case46

. In that case, the International Court of

Justice made a finding that a coastline delimitation rule put forward by the United

Kingdom would appear to be inapplicable as against Norway, inasmuch as she has

always opposed any attempt to apply it to the Norwegian coast.

Can a disagreeing State ultimately and indefinitely remain outside of new law

accepted by the large majority of States? In practice, it is highly unlikely that the

persistent objector can remain outside the scope of a new customary rule for very

long. The pressure to conform to the new rule, as well as the disadvantages of being

outside the legal regime, ensure that the objecting State cannot maintain a position

contrary to the overwhelming practice of other States.47

The subsequent objector

What is the effect of dissent by a State after a custom has been established? The

general rule is that subsequent objection to an established rule of customary law

cannot prevent that rule binding the State. A related question is what if the objecting

State was not in existence at the time that the custom came into being? The orthodox

rule is that ‘new States’ are automatically bound by generally accepted international

law. In fact the problem of the relation of new States to existing international law is

primarily a matter belonging to the area of State succession. As far as customary law

is concerned, the prevailing view is, with different reasoning, that new States cannot

in principle escape existing customary obligations. One cannot select rights granted

by a legal system and at the same time reject the duties one dislikes.48

We have to admit that subsequent objection may, over time, have a significant impact

on the substance of customary international law. It may even lead to a change in a

customary regime. Subsequent objections or derivations may become so widespread

that the previous rule is destroyed and replaced by a new rule, as with the extension of

the territorial sea from 3 to 12 miles.

(d) Local or regional custom

In the famous Asylum case between Columbia and Peru, the World Court held that:

44

Brownlie, Principles of Public International Law, 5th.ed., 1998, 10; Ahehurst’s Modern

Introduction to International Law, 7th.ed., 1997, 48; Henkin, Louis, ‘International Law: Politics,

Values and Functions” 216 Hague Recueil, 9, 45, 46, 130; Fitzmaurice, 92 Hague Recueil (1957,II),

99-100; Waldock, 106 Hague Recueil (1962,II), 49-50; Jimenez de Arechaga, 159 Hague Recueil

(1978, I) 30. 45

On the question of the persistent objector, Restatement of the Foreign Relations Law of the US

reads: “…in principle a State that indicates its dissent from a practice while the law is still in the

process of development is not bound by that rule even after it matures….” Restatement Third (1987)

vol. I, para 102, comment, 26. 46

Anglo-Norwegian Fisheries case (UK v Norway) (1951) ICJ Rep. 3. 47

This was true, for example, in respect of the UK’s objection the extension of the territorial sea

from 3 to 12 miles, a position now adopted in the UK’s Territorial Sea Act 1987. 48

The reservations of the decolonised new States towards the international legal order created by the

old colonial powers have had a considerable impact in particular areas, such as international economic

law and the law of the sea, which has led to legal uncertainty. See Akehurst’s Modern Introduction to

International Law, 7th.ed., 1997, 47.

12

The Colombian Government…has relied on an alleged regional or

local custom peculiar to Latin-American States.

The Party which relies on a custom of this kind must prove that this

custom has established in such a manner that it has become binding

on the other Party. The Columbia government must prove that the

rule invoked by it is in accordance with a constant and uniform

usage practised by the States in question, and that this usage is the

expression of a right appertaining to the State granting asylum and a

duty incumbent on the territorial State. This follows from Article 38

of the Statute of the Court, which refers to international custom as

“evidence of a general practice accepted as law”….

As the Court recognized in this case, although Article 38(1) (b) refers to “a general”

practice, it allows for local (or regional) customs amongst a group of States or just

two States49

in their relations inter se as well as for general customs binding upon the

international community as a whole. Local customs may supplement or derogate

from general customary international law (subject to such rules of jus cogens as may

exist).50

Moreover, from the wording of the judgment, it is clear that in the case of a

local custom (as opposed to general custom), the party which relies on the custom

must prove that such custom is binding upon the other party.51

3.1.4 Consistency of practice

One of the most important factors in the formation of customary law is that the State

practice must be reasonably consistent. This criterion is satisfied if there is substantial,

rather than total or complete, consistency. The International Court of Justice held in

the Nicaragua case that:

The Court does not consider that, for a rule to be established as

customary, the corresponding practice must be in absolutely

rigorous conformity with the 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….52

Therefore, major inconsistencies in the practice (that is, a large amount of practice

which goes against the ‘rule’ in question) prevent the creation of a customary rule.

As stated by the ICJ in the Fisheries case, minor inconsistencies (that is, a small

amount of practice which goes against the rule in question) do not prevent the

49

Such a custom (Portugal’s right of transit over Indian territory) was found to exist between India

and Portugal in the Right of Passage over Indian Territory case, (1960) ICJ Rep. 6. 50

Harris, D.J., Cases and Materials on International Law, 5th.ed., 1998, 25.

51 Professor D’Amato strongly argues that this requirement is meant only for local, regional or

special custom (his terminology for a local custom) and not meant for a rule of general customary law.

He quoted three World Court decisions all of which deal with local customs only, namely the Asylum

case, Right of Passage case, and Fisheries case. See D’Amato, Anthony, “The Concept of Special

Custom in International Law”, (1969) 63 AJIL 211. 52

Military and Paramilitary Activities in and against Nicaragua (US v Nicaragua) (Merits),(1986)

ICJ Rep. 14, at para 186.

13

creation of a customary rule53

, although in such cases the rule in question probably

needs to be supported by a large amount of practice, in order to outweigh the

conflicting practice in question.54

3.1.5 Duration of practice

Provided the generality and consistency of a practice are proved, no particular

duration is required: the passage of time will of course be a part of the evidence of

generality and consistency. A long (and, much less, an immemorial) practice is not

necessary, and rules relating to airspace and the continental shelf have emerged from

fairly quick maturing of practice. The International Court does not emphasize the time

element as such in its practice. In the North Sea Continental Shelf cases, the Court

suggests that “the length of time needed will vary from subject to subject and that the

passage of only a brief period of time is not necessarily a bar to the formation of

customary law”.55

The issue of instant customary law (diritto spontaneo)

An interesting issue involved in this ‘time element’ is the existence or non-existence

of the category of ‘instant customary international law’, which has been brought to the

forefront by some writers like Roberto Ago and Bin Cheng56

. The result is to deny the

significance of State practice in the formation of customary international law and to

rely solely on opinio juris as the constitutive element of custom.

In view of the nature of the decentralized international legal system and the

elementary role of State practice as the objective element in the formation of

customary law, opinio juris on its own does not suffice to establish general custom in

controversial areas. This view is confirmed by the jurisprudence of the International

Court of Justice. In the North Sea Continental Shelf cases, the Court insisted that “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 uniform”57

. An even clearer rejection of the

doctrine of ‘instant custom’ can be found in the following words of the Court in the

Nicaragua case:

The mere fact that States declare their recognition of certain rules is

not sufficient for the Court to consider these as being part of

customary international law…. Bound as it is by Article 38 of its

Statute…the Court must satisfy itself that the existence of the rule in

the opinio juris of State is confirmed by practice.58

3. 2 Opinio juris sive necessitates

Article 38(1)(b) refers to ‘international custom, as evidence of a general practice

accepted as law’. Therefore, the second element of an international custom is that the

53

Anglo-Norwegian Fisheries case, (1951) ICJ Rep. 116, at 138. 54

See Akehurst, M., “Custom as a Source of International Law” (1974-75) 47 BYIL 53 55 North Sea Continental Shelf cases, (1969) ICJ Rep., 3. 56

Cheng, Bin, “United Nations Resolutions on Outer space: Instance International customary law?”,

(1965) Indian JIL, 23. 57

North Sea Continental Shelf cases, (1969) ICJ Rep., 3, at 43. 58 Military and Paramilitary Activities in and against Nicaragua (Merits), (1986) ICJ Rep., at 97.

14

practice must be ‘accepted’ by States as ‘law’. When inferring rules of customary law

from State practice, it is necessary to examine not only what States do but also why

they do it. In other words, there is a psychological element in the formation of

customary law. State practice alone is not sufficient; it must be shown that it is

accompanied by a conviction that it is binding upon them as law. This conviction by

States in the obligatory nature of the practice is known as opinio juris sive

necessitates (in short- opinio juris).

The requirement of opinio juris

In the Lotus case59

, the PCIJ emphasized that opinio juris was an essential element in

the formation of customary international law. This was reaffirmed in the North Sea

Continental Shelf cases60

and has been accepted ever since. It is not surprising given

that there must be some criteria by which we can distinguish State practice amounting

to law from other kinds of State activity, such as acts of comity or courtesy or

friendship. In other words, opinio juris is an essential criterion for distinguishing

between law and non-law.61

Proof of opinio juris

Now that the requirement of opinio juris is established, the important problem that

remains is surely one of how to prove it. Professor Brownlie is of the view that in

terms of the practice of the International Court of Justice, there are two methods of

approach regarding the proof of opinio juris. According to him, “In many cases the

Court is willing to assume the existence of an opinio juris on the basis of evidence of

a general practice, or a consensus in the literature, or the previous determinations of

the Court or other international tribunals. However, in the significant minority of

cases (the Lotus case, North Sea Continental Shelf cases and Nicaragua case) the

Court has adopted a more rigorous approach and has called for more positive evidence

of the recognition of the validity of the rules in question in the practice of States. The

choice of approach appears to depend upon the nature of the issue, and the discretion

of the court. 62

Nevertheless, the present study respectfully submits the following:

(1) It is true that in many cases the Court was willing to assume opinio juris because

these cases were clear-cut cases where there were no sharp differences of opinions as

to the existence of a rule of customary law. If the Court has to assume opinio juris in

all cases from the existence of a general practice, then it would amount to totally

abolishing the requirement of opinio juris and determining the existence of a

customary rule entirely on the basis of general and consistent State practice.

59 Lotus case, (1927) PCIJ Series A, No. 10. 60

North Sea Continental Shelf cases, (1969) ICJ Rep. 3. 61

Kopelmanas took a position against the necessity of opinio juris, and Guggenheim argued that the

condition of opinio juris was superfluous. But this theory is untenable; it would eliminate the

distinction between rules of customary law, on the one hand, and rules of international morality and

comity, on the other. See Kunz, J.L., “The Nature of Customary International Law”, (1953) 47 AJIL,

662-669. 62

Brownlie, Principles of Public International Law, 5th.ed., 1998, 7.

15

(2) The judgment of the Court in the North Sea Continental Shelf cases is actually

rather explicit and flexible on the matter except on one point where the Court stated

that “(T)here is no evidence that (the States) so acted because they felt legally

compelled to draw (the boundary lines) in this way by reason of a rule of customary

law – especially considering that they might have been motivated by other obvious

factors.”63

The rigidity of this dictum has to be seen in the context of the practice of

non-parties upon a conventional rule, which, in the Court’s analysis, had not been

customary upon adoption of the 1958 Convention.

(3) The task of ascertaining opinio juris, although difficult, is feasible.64

The opinio

juris simply can be proved by an express, or most often tacit, acceptance of the

practice as law by the interested States. The express declaration of a State that a

given rule is obligatory (or customary) furnishes the clearest evidence as to the

State’s legal conviction. Express acceptance is, however, rather rare and not typical

for the process of custom-formation.65

(4) In most cases, the element of acceptance as law is fulfilled tacitly, only by means

of a presumption based upon various kinds of active or passive reactions to the

practice by the interested States. In the Nicaragua case, the Court indicates some

valuable guidelines on how to ascertain opinio juris:

…[A]s was observed in the North Sea Continental Shelf cases, 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 opinio

juris sive necessitatis’. 66

The Court points out that what is important in ascertaining opinio juris is the

‘behaviour’ not only of the States taking a particular action but also of other States in

a position to react to it. It is a clear guideline that opinio juris can be inferred from

the actual behaviour of States;67

it can be gathered from acts or omissions of States.68

If conduct by some States provokes ‘protests’ from other States that such conduct is

illegal, the protests can deprive such conduct of any value as evidence of customary

law.69

63

North Sea Continental Shelf cases, (1969) IC J Rep. 3, para. 78. 64

See, Villiger, M.E., Customary International Law and Treaties, Martinus Nijhoff Publishers,

Dordrecht, 1985, 27. 65

Wolfke, Karol, Custom in Present International Law, 2nd

. revised ed., Martinus Nijhoff

Publishers, Dorsrecht,1993, 47. 66

Nicaragua case, (1986) ICJ Rep., 14. para. 207. 67 The World Court itself indicated in both North Sea Continental Shelf cases and the Nicaragua

case that there is a close affinity between the two elements of State practice and opinio juris. That is

why opinio juris is to be inferred from the actual behaviour of States themselves. 68

Restatement of Foreign Relations Law of the US, (Third), vol. 1, para. 101. 69 Karl, W., “Protest”, (1986) 9 EPIL 320-22.

16

(5) “Protest”70

plays a very important role in ascertaining the element of ‘acceptance

as law’. Absence of protests or objections against a practice (that is, acquiescence)

tends to prove that States do not consider the practice as contrary to their interests

and also, that they do not object to the formation of a customary rule.71

‘Toleration’

of a practice by other States, considering all relevant circumstances, justifies the

presumption of its acceptance as law.72

(6) Casting an affirmative vote to a resolution of an international organization or

ratifying an international convention is also a clear commitment in the nature of

opinio juris on the part of a particular State. The Court states in the Nicaragua case:

As regards the United States in particular, the weight of an

expression of opinio juris can similarly be attached to its support of

the resolution of the Sixth International Conference of American

States condemning aggression … and ratification of the Montevideo

Convention on Rights and Duties of States…73

3. 3 Proof of custom

In principle, a court is presumed to know the law and may apply a custom even if it

has not been expressly pleaded. In practice, however, the proponent of a custom has a

burden of proof the nature of which will vary according to the subject matter. For

instance, in the Lotus case74

, the World Court acknowledged the plaintiff’s burden in

respect of a general custom. In a case where a local or regional custom is alleged, the

proponent ‘must prove that this custom is established in such a manner that it has

become binding on the other party’75

.

4 GENERAL PRINCIPLES OF LAW

The third source of international law listed in the Statute of the Court is ‘the general

principles of law’. Most modern jurists accept that ‘general principles of law’ are

principles of law common to all national legal systems, in so far as they are applicable

to relations of States.76

The main objective of inserting this paragraph in Article 38 is

70

Professor MacGibbon defines ‘protest’ in international law as follows: “A protest constitutes a

formal objection by which the protesting State makes it known that it does not recognise the legality of

the acts against which the protest is directed, that it does not acquiesce in the situation which such acts

created and that it has no intention of abandoning its own rights in the premises.” MacGibbon, I.C.,

“Some Observations on the Part of Protest in International Law”, (1953) BYIL 293-319, at 298. 71 See MacGibbon, “Customary International Law and Acquiescence”, (1957) BYIL 115-145. See

also Akehurst’ Modern Introduction to International Law, 1997, 44, where the learned professor makes

a distinction between a permissive rule and a rule imposing duties. 72

Governments know that toleration of practice leads to its being legalised, to the formation of a

new customary rule. Hence their increasing watchfulness. International events are watched,a nd every

situation undesirable for a State provokes an immediate reaction for fear of the consequences for that

State of its being said to have acquiesced in a precedent leading to custom. 73

Ibid., para. 189. 74 Lotus case, (1927) PCIJ Series A, No. 10, 18. 75

Asylum case, (1950) ICJ Rep. 276. 76 Akehurst’s Modern Introduction to International Law, 1997, 49; Dixon, Martin, Textbook on

International Law, 4th.ed., Blackstone Press Ltd., London, 2000, 39; Cassese, Anthonio, International

Law, Oxford University Press, 2001, 156.

17

to fill in gaps in treaty law and customary law and is necessary to meet the possibility

of a non liquet.77

Such general principles would include the duty to provide ‘reparation’ in consequence

of a wrongful act (Chorzow Factory case78

), which is accepted in most legal systems.

Some of the general principles are based on ‘natural justice’ common to all legal

systems such as the principles of good faith79

, estoppel or acquiescence80

, and

proportionalality. Some are based on legal logic or statutory interpretation such as the

principles of lex posterior derogat legi priori, lex specialis degorat legi generali, and

contra proferentem.

Perhaps the most frequent and successful use of domestic law analogies has been in

the field of evidence, procedure and jurisdictional questions. Thus there have been

references to such rules as nemo judex in causa sua (no man shall be judge in his own

cause)81

, litispendence82

, and res judicata83

. In the Corfu Channel case84

, the Court

had recourse to ‘circumstantial evidence’ and remarked that ‘this indirect evidence is

admitted in all legal systems, and its use is recognized by international decisions’.

Even some substantive law principles, though very rarely, can be found in the

decisions of the Court. In the Barcelona Traction case (Second Phase)85

, for example,

the Court has acknowledged the concept of the ‘limited liability company’ to be found

in domestic law systems.

In any case, we have to admit that the Court seldom resorted to general principles of

law. Could we say that the use of the General principles would wither away? In fact it

has not fallen into desuetude. It has remained dormant for a long time. As soon as it

has appeared that new areas of international law contained conspicuous gaps, the use

of the general principles has been revitalized. It applies in particular to international

criminal law, a body of law that is still rudimentary and replete with lacunae. In this

area the ad hoc International Criminal Tribunals (the ICTY and the ICTR) have

frequently resorted to general principles of criminal law recognized in the principal

legal systems of the world – common law systems and civil law systems. Moreover,

Article 21 of the Rome Statute establishing the International Criminal Court (ICC)

envisages the possibility that the Court might resort to such a subsidiary source.

However, as noted by Judge McNair in the South-West Africa case86

, the environment

in which international law operates is very different from the one in which domestic

law operates, and principles of domestic law can be used to fill gaps in international

law only if they are suited to the international environment.

77

Non liquet means the possibility that a court or tribunal could not decide a case because of a ‘gap’

in law. Remarkably, the ICJ applied the doctrine of non liquet in the Nuclear Weapons case, Advisory

Opinion, (1997) 35 ILM 809 and 1343. 78 Chorzow Factory case, (1928) PCIJ Series A, No. 17. 79

Nuclear Test case (Australia v France), Judgment of 20 December 1974, ICJ Rep. 1974, 268,

para, 46; See also D’ Amato, A., “Good Faith”, (1995) EPIL 11, 599-601 80

See the Eastern Greenland case, (1933) PCIJ Series A/B, No. 53, pp. 52, 62, 69; Arbitral Award

of the King of Spain, (1960) IC J Rep. 192, at 209, 213; The Temple of Preah Vihear case, (1962) IC J

Rep., at 23, 31, 32. 81

Mosul Boundary case, (1925) PCIJ Series B, No. 12, p. 32. 82

German Interests in Polish Upper Silesia, (1925) PCIJ Series A, No. 6, p. 20. 83 Effect of Awards of the UN Administrative Tribunal, (1954) ICJ Rep. 53. 84

Corfu Channel case, (1949) ICJ Rep. 18. See also Right of Passage over Indian Territory (Prelim.

Objection), (1957) ICJ Rep., 141-142. 85

Barcelona Traction case, (1970) ICJ Rep. at 33-35. 86 South-West Africa case, (1950) ICJ Rep. 148.

18

5 JUDICIAL DECISIONS AND WRITINGS OF JURISTS

Article 38(1)(d) of the Statute of the International Court of Justice directs the Court to

apply 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”.

5.1 Judicial decisions

Article 59 of the Statute says that “the decisions of the Court has no binding force

except between the parties and in respect of that particular case”. It means that in

international law there is no concept of stare decisis, as known in common law

systems.87

In theory, therefore, judicial decisions do not make law but are declaratory

of pre-existing law. They are law identifying or material sources of law, and we have

already seen that they can be evidence of customary international law.

Although international courts are, in principle, not obliged to follow previous

decisions, in practice they almost always take previous decisions into account.88

So

far as the International Court of Justice is concerned, the Court always strive to

maintain ‘judicial consistency’, referring to previous decisions. For example, in the

Interpretation of Peace Treaties case89

, the Court felt obliged to distinguish the earlier

decision of the PCIJ in the Eastern Carelia case90

, when, if one were to interpret

Article 59 strictly, this was not at all necessary.

Whatever the theory, the Court in practice is involved in the process of law-creation.

First, the Court will decide the substance of a dispute submitted to it and the decision

of the Court has created law for the parties. Secondly, and of more significance, a

decision of the Court may have a profound impact on customary law. It is often the

case that the Court will bring the process of crystallization of customary law to a swift

conclusion. It may accelerate the creation of customary law by confirming trends in

State practice and by ‘discovering’ necessary opinio juris.91

Likewise, the Court may

confirm that a principle first inserted in a treaty has now attained the status of general

customary law.92

It is also obvious that a unanimous, or almost unanimous, decision

has a role in the progressive development of the law. For example, the decisions and

advisory opinions in the Reparation93

, Genocide94

, Fisheries95

, and Nottebohm96

cases

have had decisive influence on general international law.

Since Article 38(1)(d) is not limited to decisions of the World Court, there is no

reason why decisions of other judicial bodies should not be regarded as sources of

87 See Waldock, 106 Hague Recueil (1962, II), 91. See also German Interests in Polish Upper

Silesia case, (1926) PCIJ, Series A, No. 7, p. 19. 88

Shahabuddeen, Mohd., Precedent in the World Court, 1996. 89

Interpretation of Peace Treaties case, (1950) ICJ Rep. 65. 90 Eastern Carelia case, (1923) PCIJ Series B, No. 5. 91

This seems to have happened in the angl0-Norwegian Fisheries case, and more recently, in

Tunisia v Libya in respect of the Exclusive Economic Zone. 92

See, for example, Territorial Dispute case (Libya v Chad) (1994) ICJ Rep. 6, with respect to

Article 31 of the Vienna Convention on the Law of Treaties, 1969. 93

Reparations for Injuries Suffered in the Service of the United Nations case, (1949) ICJ Rep. 174 . 94

Reservations to the Genocide Convention case, (1951) ICJ Rep. 15. 95

Anglo-Norwegian Fisheries case, (1951) ICJ Rep., 116. 96 Nottebohn case, (1955) ICJ Rep. 4.

19

international law. Even decisions of domestic courts, if they deal with matters of

international law, may provide important evidence as to the practice of States,

particularly in fields such as State immunity, extradition, international personality and

human rights. The Pinochet case97

is a good example.

5. 2 Writings of publicists

The writings of the most highly qualified publicists are also to be regarded as a

‘subsidiary means for the determination of rules of law’, although it is clear that they

are a material or evidential source only. Today, the writings of even the most

respected international lawyers cannot create law. While international arbitral

tribunals frequently cite textbooks and authors, the International Court of Justice

refrains from doing so in its decisions.98

6 OTHER POSSIBLE SOURCES

Having examined the sources mentioned in the Statute of the Court, our concern now

is to consider whether there are any other possible sources, which have been omitted

in the list.

6. 1 General Assembly Resolutions

There have been suggestions that the resolutions of the United Nations General

Assembly should be recognized as a source of international law. As a rule, General

Assembly resolutions are not binding on member states; in fact most resolutions have

nothing to do with international law. Nevertheless, when they are concerned with

general norms of international law, they may provide a basis for progressive

development of the law and the speedy consolidation of customary rules.99

As Sloan suggests, General Assembly resolutions may also contribute to custom more

directly in a form of “collective State practice”.100

They are the collective equivalent

of unilateral general statements or, in the context of a particular dispute, ‘150

diplomatic protests’. The process by which they are adopted (“adopted unanimously,

or near unanimously, or by a true consensus’ or otherwise) establishes whether the

practice is a “general’ one. Their repetition in later resolutions goes to the ‘constancy’

and ‘uniformity’ of the practice. As to the requirement of opinio juris, this will be

evidenced, as Sloan indicates, by the wording of the resolution; by statements made in

the General Assembly in debate prior to its adoption or later in explanation of a vote;

or by statements made elsewhere.

97

Pinochet case – R v Bow Street Metropolitan Stipendiary Magistrate, ex parte Pinochet (No. 3),

[1999] 3 All ER 97. 98 See Rosenne, The Law and Practice of the International Court of Justice , 2nd.ed., 1985, 614-16. 99

Examples of ‘law-making resolutions’ are the Resolution which affirmed the Principles of

International Law recognised by the Charter of the Nuremberg Tribunal and the Judgment of the

Tribunal (Res. No. 95, 11 Dec. 1946, adopted unanimously); the Declaration on Granting of

Independence to Colonial Countries and Peoples (Res. No. 1514, 14 Dec. 1960, adopted by 89 votes to

none, with 9 abstentions); and the Declaration on Permanent Sovereignty over Natural Resources, (Res.

No. 1803. 14 Dec. 1962, adopted by 87 votes to 2, 12 abstentions). 100

Sloan, “General Assembly Resolutions Revisited”, (1987) 58 BYIL 39. For a different view, see

MacGibbon, in Cheng, ed., International Law: Teaching and Practice, 1982, 59.

20

International courts and tribunals have not doubted that General Assembly resolutions

are State practice and hence evidence of custom. Moreover, they have tended to give

considerable weight to them as such. We should note the use of the Court of the

General Assembly resolutions on self-determination in the Western Sahara case101

.

and the reliance by various arbitral tribunals on the GA Resolution 1803 (Permanent

Sovereignty over Natural Resources) on the rules on expropriation.102

Most strikingly,

the judgment of the World Court in the Nicaragua case103

relies almost exclusively

upon General Assembly resolutions104

when stating the law on the use of force and

intervention. In the Legality of the Threat and Use of Nuclear Weapons case105

, the

Court stated that:

The General Assembly resolutions, even if they are not binding,

may sometimes have normative value. They can …provide evidence

important for the emergence of an opinio juris…. a series of

resolutions may show the gradual evolution of the opinio juris

required for the establishment of a customary rule.

6. 2 Soft Law

In recent years a new idea has crystallized in the international community, which has:

come to be known as ‘soft law’106

(as opposed to ‘hard law’, which makes up

international law proper). ‘Soft law’ can be defined as a body of guiding principles,

standards, rules of conduct, or declarations of policy, which are not strictly binding

norms of law.107

Some argue that this is not law at all but another name for principles

de lege ferenda, or principles which could become normative in the future. 108

Some

say that there exists a considerable “grey area” of “soft law” between the white space

of “law” and the black territory of “non-law”.109

Soft law can be found, for example, in treaties not yet in force, in resolutions or

declarations of international organizations, or in final acts of international

conferences. It chiefly relates to human rights, international economic relations, and

protection of the environment. Some examples of soft law instruments are: the

Helsinki Final Act 1975, the Bonn Declaration on International Terrorism 1978, and

the Rio Declaration on the Environment and Development 1992.

101

Western Sahara case, (1975) ICJ Rep. 12. 102

See, for example, The Texaco case (1977) 53 ILR 389; The Aminoil case, (1982) 21 ILM 976. 103

Nicaragua case (Merits), 1986 IC J Rep. 14. 104 Especially General Assembly Resolution 2625(XXV) of October 24, 1970 which is entitled

“Declaration on Principles of International Law Concerning Friendly Relations and Co-operation

among States in accordance with the Charter of the United Nations”. The Resolution was adopted by

the General Assembly without a vote (that is, by consensus). 105 Legality of the Threat and Use of Nuclear Weapons case, Advisory Opinion, (1996) ICJ Rep. 66. 106

The concept of soft law has, however, been criticised by some writers: “The term is inadequate

and misleading. There are no two levels or ‘species’ of law – something is law or not law:” Criticism of

Sztucki, cited in Harris, D.J., Cases and Materials on International Law, 5th.ed., 1998, 65.

107 On soft law generally, See Chinkin, “The Challenge of Soft Law: Development and Change in

International Law”, (1989) 38 ICLQ 859; Weil, “Towards Relative Normativity in International Law”,

(1983) 77 AJIL 413. 108

Dixon, Martin, Textbook on International Law, 2000, 48. 109 Van Hoof, Rethinking the Sources of International Law, 1983, 187-89.

21

These soft law instruments have, according to Professor Antonio Cassese, three major

features in common. First, they are indicative of the modern trends emerging in the

world community. Secondly, they deal with matters that reflect new concerns of the

international community, to which previously this community was not sensitive or not

sufficiently alert. Third, for political, economic, or other reasons, it is, however, hard

for States to reach full convergence of views and standards on these matters so as to

agree upon legally binding commitments.110

While it may be paradoxical to call something “law” when it is not law, the concept is

nonetheless useful to describe instruments that clearly have an impact on international

relations and that may later harden into custom111

or become the basis of a treaty.112

6. 3 Equity

Equity is used here in the sense of considerations of ‘fairness’, and ‘reasonableness’.

It is the application of rules of international law with due regard to what is fair and

reasonable.

In the Diversion of Water from the Meuse case113

, the Netherlands claimed that

Belgium had violated a treaty by building canals that changed the flow of water in the

River Meuse. One of the issues was whether the Netherlands had lost the right to

bring the claim because of similar earlier conduct by itself (estoppel). In this

connection, the individual opinion of Judge Hudson recognized the principle of

‘equity’ as part of international law. He noticed that there was no express authority in

the Statute of the PCIJ to apply equity as distinguished from law. But he pointed to

Article 38(1)(c) of the Statute which allowed the application of ‘general principles of

law’ and argued that principles of equity are common to all national legal systems.

References to ‘equity’ can be found very often in the judgments of the World Court.

Examples include the River Meuse case itself (application of equitable principle of

estoppel), the Temple of Preah Vihear case114

(application of acquiescence),

Barcelona Traction case115

(reference to “considerations of equity” when seeking to

apply the law of diplomatic protection “reasonably”), and the Frontier Dispute case

(Burkina Faso v Mali)116

(application of equity infra legem117

,that is, that form of

equity which constitutes a method of interpretation of the law in force, to territorial

delimitation).

Perhaps the most prominent use of equity as part of international law has been in the

law of the sea in the context of delimitation of maritime zones. In the Fisheries

110

Cassese, Antonio, International Law, Oxford University Press, 2001, 160-1. 111

For instance, the University Declaration of Human Rights 1948 was “soft Law” when it was

adopted but has since to some extent hardened into custom. See Filartiga v Pena-Irala, 630 F.2d 876

(1980). 112

For instance, the United Nations Declaration on Torture 1975, GA Resolution 3452, formed the

basis for the later adoption of the Convention Against Torture and Other Cruel, Inhuman or Degrading

Treatment or Punishment 1984. 113 Diversion of Water from the Meuse (Netherlands v Belgium), (1937) PCIJ Series A/B, No. 70. 114

Temple of Preah Vihear case, (1962) ICJ Rep. 6. 115

Barcelona Traction case (Belgium v Spain), (1970) ICJ Rep. 3, at paras. 93-94. 116

Frontier Dispute case (Burkina Faso v Mali), (1986) ICJ Rep. 554. 117 See Akehurst, M., “Equity and General Principles of Law”, (1976) 25 ICLQ 801.

22

Jurisdiction case118

, the Court outlined the elements of an ‘equitable solution’ of the

differences over fishing rights and directed the parties to negotiate accordingly. In the

North Sea Continental Shelf cases119

, the Court had to resort to the formulation of

equitable principles concerning the delimitation of adjacent areas of continental shelf,

as a consequence of its opinion that no rule of customary or treaty law bound the

States parties to the dispute. The Court has increasingly referred to “equity” in its

judgments in recent years. For example, in the Gulf of Maine case120

, it stated that the

concepts of acquiescence and estoppel in international law “follow form the

fundamental principles of good faith and equity”.

The conclusion then is that ‘equity’, in the present context, is encompassed by

Article 38(1)(c) of the Statute, that is, as a general principle of law, and not by

Article 38(2) which empowers the Court to decide a case ex aequo et bono, if the

parties agree thereto121

.

7 THE HIERARCHY OF THE SOURCES

There is no indication in Article 38 of the Statute of the priority or hierarchy of the

sources of international law. Apart from a single reference to ‘subsidiary means’ in

Article 38(1)(d), we do not know the order in which the sources of law are to be

applied. When drafting the original text of article 38, words of priority were included:

“the sources listed should be considered by the Court in the undermentioned order

(i.e., the order (a) to (d) in which they now appear)”; but ultimately they were

deleted.122

The silence in Article 38 as to a hierarchy of sources reflects accurately the

nature of the international legal order in which a hierarchy of sources is an alien

concept. Indeed, there is no difficulty if the rules derived from the various sources are

complementary. However, in cases of conflict it is vital to determine which source

shall prevail. The state of the law relating to the hierarch or priority among the various

sources of international law can be summarized as follows:

(1) Jus cogens: the highest in the hierarchy

A rule of jus cogens is a peremptory norm of general international law, which 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”.123

The

typical effect of rules of jus cogens is that as States cannot derogate from them

118

Fisheries Jurisdiction case (UK v Iceland), (1974) ICJ Rep. 3, at 30-5. 119 North Sea Continental Shelf cases, (1969) ICJ Rep. 3, at 46-52. 120

Gulf of Maine case, (1984) ICJ Rep. 246, at 305. 121

Article 38(2) refers to a decision by the Court where equity overrides all other rules. This is the

power of the Court to decide a dispute at the request of the parties without any reference to

international law at all. It has never been used by the Court. 122

Akehurst, M., “Hierarchy among the Sources of International Law”, (1974-75) 47 BYIL, 273.

Professor Harris refers to the oppositions at the meeting of the Advisory Committee of jurists, namely:

(1) if the expression [undermentioned order] only meant that a convention should be considered before,

for instance, customary law, it is unnecessary because it is a fundamental principle of law that a special

rule goes before general law; (2) This expression also seems to fail to recognise that these various

sources may be applied simultaneously. See Harris, D.J., Cases and Materials on International Law,

5th.ed., 1998, 23.

123 See Article 53 of the Vienna Convention on the Law of Treaties 1969.

23

through treaties or customary rules (which are not endowed with the same legal

force), the treaty or customary rules contrary to them are null and void.124

Therefore,

rules having the character of jus cogens are the highest in the hierarchy of the sources

of international law.

(2) Treaty versus custom

Our concern here is the interaction between the two major sources of international

law: ‘treaty and custom’. They are both necessary components of the international

order. Usually, they are quite complementary. A treaty may codify custom or may

lead to the development of new customary law through the impetus it gives to State

practice. On the other hand, States may abrogate a customary rule by concluding a

treaty125

; the latter may again be modified by new customary law.126

Therefore, the

conclusion is that treaty law and customary law are of equal authority and of equal

status (with the exception of the principle of jus cogens).

Difficulties can arise, however, if the treaty and customary law stipulate contradictory

or dissimilar obligations. In case of conflict, which law shall prevail? One solution

can be found in the principle of lex posterior derogat legi priori (a later law repeals an

earlier law). When two rules on the same subject matter differ in their contents, the

rule originating later in time shall prevail.127

However, There are some difficulties in

the application of this principle: (1) The principle raises the problem of determining

the precise moment of the formation of a customary rule; (2) a new particular

customary or conventional rule may arise leaving the general one unchanged for the

remaining members of the international community or the parties to the multilateral

treaty; and (3) in the case of codification of a customary rule, there is no ground for

automatic abrogation of an old, well-settled general rule in so far as it does not

contradict the codified one.128

In deciding possible conflicts between treaty law and customary law, two other

principles must also be observed. The first one is lex specialis derogat legi generalis

(A special law prevails over a general law).129

The second one is Lex posterior

124

Cassese, Antonio, International Law, 2001, 143. 125

One of the main reasons why States make treaties is because they regard the relevant rules of

customary law as inadequate. Thus States may derogate from customary law by concluding a treaty

with different obligations, the only limitation being rules of jus cogens. See Akehurst’s Modern

Introduction to International Law, 1997, 56. 126

Treaties can come to an end through ‘desuetude’ –the situation in which the treaty is consistently

ignored by one or more parties, with the acquiescence of the other party or parties. Desuetude often

takes the form of the emergence of a new rule of customary international law, confliction with the

treaty. See Kontou, N., The Termination and Revision of Treaties in the Light of New Customary

International Law, 1994. 127 Villiger, M.E., Customary International Law and Treaties, Martinus Nijhoff Publishers, Dordrecht,

1985, 36. 128

Wolfke, K., Custom in Present International Law, 2nd

.rev.ed., Martinus Nijhoff Publishers,

Dordrecht, 1993, 114-5. 129 Whether a rule is lex specialis or not can be determined ratione personae, that is regarding the

number of those that are bound by the rule. In this sense, a rule can be a lex specialis if it binds few

States, as opposed to a convention with many parties, or to a general customary rule, which is binding

erga omnes. A rule can also be special, ratione materiae, in that it furnishes, in comparison with lex

generalis, the deeper, more detailed, perhaps exceptional, regulation on the same subject-matter.

24

generalis non derogat legi priori specialis (a later law, general in nature, does not

repeal an earlier law which is more special in nature).130

(3) Inconsistent treaties

If there are successive treaties relating to the same subject matter, which treaty shall

prevail? The answer can be found in Article 30 of the Vienna Convention on the Law

of Treaties 1969, which is to be applied subject to Article 103 of the United Nations

Charter.131

The essence of Article 30 is that ‘when all the parties to the earlier treaty

are parties also to the later treaty, then the general rule of lex posterior derogat legi

priori applies and the later treaty shall prevail over the earlier treaty’.132

Article 103 of the Charter: Clause paramount

Article 103 of the Charter reads: “ In the event of a conflict between the obligations of

the Members of the United Nations under the present Charter and their obligations

under any other international agreements, their obligations under the present charter

shall prevail”. This article is known as ‘clause paramount’ and it clearly

acknowledges the supremacy of the UN Charter over any other treaties. In the

Lockerbie case (Provisional Measures)133

, the International Court of Justice confirms

this and held that by virtue of Article 103, obligations of the parties under the UN

Charter (that is, the SC Resolution 748) prevail over their obligations under the

Montreal Convention.

(4) General Principles of Law and Other sources

Since the main function of general principles of law is to fill gaps in treaty law and

customary law, it would appear that treaties and custom prevail over general

principles of law in the event of conflict. Judicial decisions and learned writers are

described in Article 38(1)(d) as ‘subsidiary means for the determination of rules of

law’, which suggests that they are subordinate to the other three sources listed:

treaties, custom and general principles of law. Judicial decisions usually carry more

weight than learned writers, but there is no hard and fast rule; much depend on the

quality of the reasoning which the judge or writer employs.

8 CONCLUSION

Custom and treaties constitute the two most important sources of international law. A

distinctive feature of international law making is the absence of any hierarchy

between custom and treaties as sources of law. They are of equal rank and status.

130

See the comment of Ago in the ILC, Yearbook of the ILC, 1966 vol. 1, Part 2, 167, para 50. 131 Article 30(1) of the Vienna Convention on the Law of Treaties 1969. 132

Article 30(3), Ibid. However, According to Article 30(4),

“When the parties to the later treaty do not include all the parties to the earlier one:

(a) as between States parties to both treaties the same rule applies as in paragraph 3;

(b) as between a State party to both treaties and a State party to only one of the treaties, the

treaty to which both States are parties governs their mutual rights and obligations.” 133

Case Concerning Questions of Interpretation and Application of the 1971 Montreal Convention

arising from the Aerial Incident at Lockerbie (Libya v UK) (Libya v United States), (1992) ICJ Rep. 3,

114.

25

Nevertheless, in recent years, a new category of international rules has come into

being: jus cogens or peremptory norms of general international law. States may not

derogate from jus cogens through treaties or customary rules. It follows that jus

cogens is hierarchically superior to all the other rules of international law.

Having said that, we can now summarise the main points on the application of the

sources of international law.

(1) If there is a treaty binding the two parties to a dispute, it is quite logical that the

Court will, first of all, look at the treaty, which is a jus scriptum. Even in such a

situation, however, we cannot say that customary law is entirely irrelevant. There

may be quite a number of legal issues involved in the dispute. The treaty cannot

have solutions to all of them. The Court, unavoidably, has to apply customary law

to deal with issues in respect of which there are no answers in the treaty. In a

number of cases, the Court will need to apply customary law to interpret the

provisions of the treaty. Therefore, it appears that the Court in most cases apply

both treaty law and customary law simultaneously.

(2) If there is no treaty binding the two parties to a dispute, then the Court has to rely

exclusively on customary international law for the determination of the dispute.

(3) If no relevant rule can be found in treaty law and customary law, the Court may

apply the general principles of law accepted by most national legal systems.

‘Equity’ is applied by the Court as a general principle of law.

(4) Judicial decisions and writings of publicists are subsidiary means for the

determination of the rules of law. Judicial decisions appear to have more weight.

Even though in theory there is no doctrine of binding precedent in international

law, in practice the Court always refer to its previous decisions and has

established its jurisprudence.

(5) Judicial decisions, resolutions of the General Assembly, national legislation, and

the like are the material sources of international law and they can be the evidence

of customary law.