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L’ordre juridique international entre tradition et innovation

Christian Dominicé

Première partie. Théorie générale du droit des gens

Methodology of International Law1

Texte intégral


  • 1 Paru dans Encyclopedia of Public International Law, vol. 7, 1984, pp. 334-339. © North-Holland, Ams (...)

1Methodology seeks to define the means of acquiring scientific knowledge.

2There is no generally accepted definition of the methodology of international law. In this article it will be taken to comprise both its wider meaning of the methods used in the acquisition of a scientific knowledge of the international legal system and its narrower and more specialized meaning, the methods used to determine the existence of norms or rules of international law.

3The correlation of these two notions is evident, for a legal system is defined as being an aggregate of interlinked legal rules which constitute the whole system, while a legal norm is recognized as such by reference to the legal system to which it belongs and whence it originates.

4These methods belong to the sphere of legal science. The latter is often described as a normative science, but this in fact is not the case. Law itself is normative because it prescribes what has to be, but legal science, like any other science, aim at the acquisition of knowledge. Its subject is the study of rules and, generally, of the legal phenomenon, but it is not a normative science.


5a) The various doctrines of international law (International Law, Doctrine and Schools of Thought in the Twentieth Century) embody global conceptions from which the principles on which the determination of legal norms is based are generally derived. In this context, we are concerned only with methods of analysis of the international legal system.

6b) The first method is that of observation free of any preconceptions. It is related to the sociological approach which perceives law as a social fact.

7We can observe that within the framework of international society, whose basic structure is a plurality of sovereign States, there exists a system of legal rules termed and recognized as such. This conclusion is buttressed by the finding that there is a sort of collective opinio juris, a conviction that international law exists and that States could not do without it. There is no need to seek a theoretical foundation to justify this assertion, which results from a mere observation of reality and is expressed by the maxim ibi societas ibi jus. The empirical method also allows us to conclude that law – or more precisely, the idea of law – is a creation of the human mind, a rationalization based on the perception of social needs. It is at this stage that we reach the limits of the empirical method.

8c) The idea of law satisfies the need for organizing and regulating society. Thus logical reasoning, which is located on a higher plane than that of formal legal techniques, is also used as a method of analysis. Its results are verified by the empirical method, but it is the reasoning which supplies the ideas and provides the syntheses which permit a global view of a legal system.

9This reasoning leads one to seek the modes of formation of legal norms and to rationalize these modes. It also highlights the logical impossibility of a legal rule which lacks a subject, and hence develops the concept of subjects of legal rules (Subjects of International Law). Other such examples could be adduced, but those given above are sufficient to illustrate the method of logical reasoning applied to the idea of law.

10d) Thus, empirical observation and logical reasoning are the two methods which, when coordinated, allow us to analyse the international legal order and to explain its characteristics. The results of this analysis are not considered here, as we are concerned only with methodology which, to remain scientific, must eliminate preconceived dogmatic notions and non-verified hypotheses.


11a) The methods to be defined are distinct from substantive law in that they seek to determine the various rules of the latter. For example, a judge has to use these methods to determine the rules which he will apply in a certain case; he must determine the existence of these rules and, hence, their content. This methodology is distinct from the theory of international law, whose subject is the international legal system as such, together with its foundations and structure. However, the separation is not complete.

12b) The methods used to determine the existence of rules in fact are sometimes closely bound up with the general conception of the fundamental aspects of the international legal system. Thus, for example, the normativist school considers that every norm of international law is derived by logical deduction from a preceding norm.

13c) The methods of determining the rules of international law must also be distinguished from the methods and techniques of application of each rule to a concrete case. The application of a rule of international law occurs after that rule has been identified and its existence proved. However, in this case as well the separation is not watertight. There are some points of contact. Thus, in a given situation the search for an applicable rule might give rise to the problem of analogy or that of the absence of relevant legal rules; these problems are on the borderline between the determination of legal rules and their application.

14d) The methodology of international law, in the sense in which it is defined here, does not include the means of analysis used to explain the reasons or motives which are at the root of rules of law and determine their content. The appearance of a rule and the directions it gives are the result of the play of forces and conflicts of interests in international society, of the influence of ideologies and philosophies, and also of the needs of society. The analysis of these phenomena belongs to the sphere of the sociology of international law which, in turn, has its own methods.

15It is noteworthy, however, that when we seek to prove the existence of a concrete rule of international law, the different factors which we must take into account in order to establish this proof sometimes include the rational grounds for its existence, or – to put it in other terms – the motives which explain and vindicate its content.


16a) When analysing various doctrinal approaches it is important to distinguish the elements which belong to methodology in the narrow sense of the term from those which belong to general conceptions of international law. It is not always easy to draw this distinction. For example, various positivist schools are founded on the idea that legal rules are created by a process of formation which is itself regulated by law and based on a single principle; that principle differs, according to the given school. According to these conceptions, the determination of the rules of international law relies mainly on deduction. Schwarzenberger, one of the principal theoreticians of the inductive method, for his part presents it as a positivist method. Hence, the terminology used to designate the various doctrinal schools of international law should be avoided; it is better to confine oneself to terms which apply specifically to methods.

17b) The inductive method favours the identification of the rules of law by the observation of their effectiveness in international society. It considers a rule to be a rule of law if it is recognized as such by the subjects of international law. Whether this is the case is revealed by practice, taken in its widest sense. Hence, this is an empirical method. It does not deny the utility of other methods, such as deduction or reasoning, but the results of the application of these methods are considered as hypotheses which must be verified by empirical observation.

18c) The deductive method, on the other hand, determines the existence of rules of international law by a process of reasoning based on principles, legal facts or on formal modes of creation, which are the foundations of the validity of the rules. Given the great variety of schools of thought using the deductive method a complete description is not possible here; rather we must confine ourselves to a few examples.

19The natural law school considers that legal norms owe their validity to that immanent law whose expression they are. Various currents within positivism hold that rules owe their existence to the fact that they have been “laid down” or created by certain concrete facts, for example, by acquiescence or a sort of collective will. This method finds its highest expression in the normativist school, which considers the existence of any legal norm as established by logical deduction from a preceding and hierarchically superior norm, this process continuing until we arrive at the “basic hypothetical norm” (Grundnorm). The deductive method comprises also the reasoning based on the analysis of the legal phenomenon, which leads to the determination of certain principles.

20d) The inductive and deductive methods are not necessarily mutually exclusive. Their combined utilization within the framework of the international legal order can be envisaged, and several writers have proposed it.


21a) The method of determining norms cannot be dissociated from the sources of international law. Indeed, it is impossible to determine the rules which are in practice effective without having a guide for this search. Only the knowledge of the manner in which these norms might exist or be created can serve as such a guide.

22b) The sources of international law are known; their definition corresponds to the observations which can be made and to the conclusions of logical reasoning. The determination of the sources of international law, however, belongs to the sphere of the methodology used to study international law as a legal system (i.e. methodology in its wide meaning).

23One admits the existence of rules “laid down” by virtue of a preceding norm and of rules created “spontaneously”; one further includes in the category of sources the “principles”, about which opinions vary considerably.


24a) The international legal system comprises many norms resulting from acts of will. The will cannot produce any legal effects by itself; an existing norm must endow it with legal effect. An international treaty, a unilateral enactment made – within its competence – by an organ of an international organization, the decision of a tribunal creating legal rules valid inter partes (International Courts and Tribunals), these all owe their validity to a preceding and hierarchically superior legal rule.

25It could be claimed that the rules created by legal acts could be determined with the help of the inductive method, by observing their effectiveness. However, the limits of what this method can achieve are clearly marked. The normal way for a judge, for example, to proceed is to determine whether a rule exists (because it is valid) before applying it. The question of validity of the rules laid down is examined when taking into account the rules governing competence, the procedure followed, etc. It is the deductive method which must be used, as demonstrated by awards resulting from the judicial application of a conventional rule or of a provision of a resolution of an international organization (International Organizations, Resolutions). If the point in question is challenged, the judge makes sure that the rule is contained either in a treaty which is validly concluded and is in force at the relevant moment or in a unilateral act validly enacted and possessing force of law. This assertion is proved by the following fact: If it is found that a treaty which has been in force for some time has a nullifying defect, its provisions cease to be legal rules, even if they have been effective. According to the Vienna Convention on the Law of Treaties (Article 69) the consequences of the application of conventional rules whose invalidity has been established must as far as is possible be obliterated. In the Sovereignty over Certain Frontier Land case (Belgium/Netherlands) it was found that sovereignty vested in Belgium by virtue of a convention was not affected by the fact that the Netherlands had exercised several acts of sovereignty (ICJ Reports, 1959, at pp. 227–230); its validity having been established, the convention was considered to have priority.

26b) Hence, insofar as the aggregate of rules laid down by a legal act is concerned, we must apply the deductive method. However, it is sometimes necessary to seek verification, and this can be done only with the aid of the inductive method. Indeed, it may happen that a conventional rule falls into abeyance as a result of a different practice having become effective and having generated a custom replacing that rule.

27c) The determination of “laid down” rules – like any other rules – cannot be dissociated from the determination of their content. As far as rules of this type – i.e. written rules – are concerned, the determination of any given rule leads first to a text whose validity is verified, and afterwards the problem of its interpretation arises (Interpretation in International Law). Hence, there are two successive stages in the determination of a rule and its content; and it is during the second stage that various methods of interpretation may be used.


28Norms of customary international law do not owe their validity to any pre-existing rule. They are norms spontaneously created.

29Such rules are determined by the inductive method. It is by observation of practice, behaviour and attitudes that we determine the existence of a norm, established by its effectiveness. It must be emphasized, however, that as far as customary law is concerned, the determination of a rule and that of its content is frequently one and the same operation. The question one has to ask oneself is: Does a rule having a certain content exist? Considerations of common sense, of equity (Equity in International Law) and of necessity might buttress the proof of its existence and are sometimes necessary. In the Anglo-Norwegian Fisheries case (ICJ Reports, 1951, at p. 133) the International Court of Justice formulated what it called “certain basic considerations” related, in particular, to the nature of the territorial sea (Territorial Waters) and to certain economic interests peculiar to a region (Fisheries Case (U.K. v. Norway)). This example illustrates that while the method of determination of customary rules is mainly inductive, in the verification of the content of a norm, it also takes into account various factors comprised of different considerations including ethical ones, as demonstrated by the judgments referring to considerations of humanity (see, for example, the Corfu Channel case (Merits)). Hence, the inductive method employed in the determination of spontaneously created rules of law must be supplemented by other considerations supplied by reasoning.


30a) Various rules which show a certain degree of abstraction and are, in fact, but a cluster of customary rules, are sometimes called “principles” or even “fundamental principles”. Consequently, there is no need to inquire into the method which should be used for their determination or identification. It is purely a question of synthesis and classification.

31b) The “general principles of law” referred to in Article 38 (1) (c) of the Statute of the ICJ are those which are generally sanctioned in foro domestico. A first consideration is that, in so far as it concerns technical rules, the method used to determine these “general principles” is that of observation, which has an inductive character. The judge examines national legal systems in order to extract from them the rule he will apply. However, he must establish the existence of an analogy between the situation considered and that envisaged by the municipal laws which is sufficient to justify the derivation of a rule from them. This implies a comparative analysis and a certain degree of reasoning.

32Secondly, there are principles of a special character which are necessarily present in any legal system, including the international legal system. For example, the norm pacta sunt servanda is intimately bound up with the very idea of law, for one of the first and most essential manifestations of that idea is the mutual engagement considered as obligatory. Similarly, the principle according to which the breach of an obligation to a subject of law involves the duty of reparation is inherent in any legal system, because the idea of legal obligation becomes meaningless if it makes no difference, on the legal plane, whether an obligation is fulfilled or not. In this connection one might also mention the principle of good faith.

33The inductive method may be used to determine the existence of these principles, but it must be emphasized that because they are inherent in any legal system, they are unalterable and cannot change, as do principles of customary origin. On the level of methods, it must therefore be emphasized that these principles are identified by a process of reflection upon the nature of law. Their effectiveness is sometimes precarious, as in respect of the duty of reparation for an illegal act, but they remain, nevertheless, fully valid legally.

34c) Could the same method of logical and deductive reasoning lead to the determination of principles peculiar to the international legal system and inherent in it? Logical reasoning leads us to the conclusion that the principle of sovereignty has these characteristics. Several writers present it as an abstraction from customary rules. In the author’s opinion, however, the scientific analysis of the international legal system shows that it is founded entirely on a plurality of sovereign States which are its primary subjects, and it functions within this context. If this characteristic feature of it disappeared, we would find ourselves confronted with a legal system different from the one we know today. This implies the principle of sovereignty: We are led to this conclusion by the global analysis of the international legal phenomenon, as well as by reasoning, i.e. by a combination of observation and logical deduction.


35a) Methodology in the narrow meaning of the term does not include the application or enforcement of the rules of international law. Indeed, the latter take place only subsequent to the determination of rules applicable to a given case. However, it sometimes happens in a particular situation that there exists neither a rule of international law nor the possibility of being guided by national laws (see Article 38 (1) (c) of the ICJ Statute) because the analogy is not sufficient. This is the problem of lacunae and in the same context the problem of analogy arises. These problems cannot be treated here in detail; only a few methodological observations may be presented.

36b) The problem of lacunae must be approached by reasoning. The latter leads certain writers to maintain that where there are no rules, the necessary conclusion by virtue of the principle of liberty, bound up with sovereignty, is that no obligation is assumed by the State. This deduction seems logical, but cannot be considered a safe guide in all situations.

37Indeed, logical analysis illustrates that certain situations necessarily require a solution, because the liberty of action or sovereignty of several States are in conflict with one another. As an example we might mention certain territorial problems (boundaries, international rivers) which arise when new or unsolved questions emerge.

38The rule or the principle of solution for an individual case may be determined with the help of analogy or considerations of common sense and equity. However, the judge must not exceed the powers conferred upon him.

39A special category of lacunae – sometimes called “non-authentic” lacunae – is the one created by unintentional omissions or the incomplete drafting of a text, particularly the text of a convention. A solution might be found by analogy with a similar text or the elaboration of a rule, if the organ referred to is empowered to do so. There is no single method.

40c) Analogy has already been referred to in connection with the problem of lacunae. Its use is certainly authorized in international law, as practice shows. It is more difficult to fix the limits of its use. From the methodological point of view the problem is this: After having identified a rule one must extend its application to cover a case, situation or legal relationship not explicitly envisaged by it – or at least let that rule inspire a solution. It is the comparative analysis of the situation governed by this rule and of that to which one would like to extend its application which reveals whether such a procedure is acceptable. The similarity of the two situations must be evident.

41This question might arise especially in connection with the external relations of international organizations (International Organizations, Implied Powers; International Organizations, Treaty-Making Power). It is true that autonomous rules governing these relations tend to develop, but situations might arise where such rules do not yet exist. If the analogy with the situation of a State is sufficient, it is possible to envisage the application of rules developed in inter-State relations. Thus, when the League of Nations established itself in Geneva, the Swiss Government considered that as the League had international personality it was, “consequently, entitled to have the status of a State”. As a result the League obtained the benefit of jurisdictional immunities granted to States (Provisional Modus Vivendi of 1921 between the League of Nations and the Swiss Federal Council concerning the regime of diplomatic immunities of the staff of the League of Nations and of the International Labour Office; International Organizations, Privileges and Immunities). Since then the legal status of international organizations in host States has become the object of many agreements which provide for a legal status different in certain respects from that applied to States. In 1921 Switzerland proceeded by analogy, extending the application of rules governing relations between States to another subject of international law, what situation was thought to be similar.

42d) In short, the identification of rules of international law leads to the determination of their subjects and of the facts or situations to which they apply. In a case for which no relevant rule of international law can be found, logical reasoning makes it possible to determine whether such a situation implies liberty of action or whether, on the contrary, some form of regulation is necessary; the latter is applicable especially where its absence would lead to a conflict between several States exercising their liberty of action, or when the results of such a situation would be unsatisfactory. Application by analogy then becomes possible through the extension of the rule either to cover other subjects or a situation very similar to that to which the existing rule applies.


43The methodology of international law is determined by two elements. On the one hand, any scientific approach is based on observation free of any preconceived ideological or doctrinal notions. On the other hand, the object of observation, i.e. the international legal system and its various rules, originates from the idea of law, which is a creation of the human mind, a rationalization. It follows that observation itself cannot be entirely free from rational elements. We have seen, for instance, that the inductive method of determination of rules rests on the notion of sources. Consequently, the method of scientific analysis of the international legal system and of the rules of which it is composed is a combination of inductive and deductive elements, of observation and of reasoning. The role and the function of each of these elements need to be clearly defined.

44F. Castberg, “La méthodologie du droit international public”, RCADI, vol. 43, 1933-I, pp. 313-383.

45R. Ago, “Science juridique et droit international”, RCADI, vol. 90, 1956-II, pp. 859-958.

46A. Schüle, “Methoden der Völkerrechtswissenschaft”, AVR, vol. 8, 1959-1960, pp. 129-150.

47G. Schwarzenberger, The Inductive Approach to International Law, 1965.

48J. Salmon, “Quelques observations sur les lacunes du droit international public”, Revue belge de droit international, vol. 3, 1967, pp. 440-458.

49Ch. de Visscher, “Méthode et système en droit international”, RCADI, vol. 138, 1973, pp. 75-79.

50R. Yakemtchouc, “L’approche sociologique du droit international”, RGDIP, vol. 78, 1974, pp. 5-39.

51A. Bleckmann, “Analogie im Völkerrecht”, AVR, vol. 17, 1977, pp. 161-180.

52M. Bogdan, “General Principles of Law and the Problem of Lacunae in the Law of Nations”, NordTIR, vol. 46, 1977, pp. 37-53.

53Ch. Dominicé, “Observations sur la définition du droit des gens”, Festschrift für Rudolf Bindschedler, 1980, pp. 71-90.

Notes de fin

1 Paru dans Encyclopedia of Public International Law, vol. 7, 1984, pp. 334-339. © North-Holland, Amsterdam.

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