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Max Planck Encyclopedia of Public International Law [MPEPIL]

Legal Positivism

Jörg Kammerhofer

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Encyclopedia entries
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Max Planck Encyclopedias of International Law [MPIL]

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Max Planck Encyclopedia of Public International Law [MPEPIL]
Article last updated:
January 2023

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2023. All Rights Reserved.date: 01 October 2023

Subject(s):
Theory of international law

Published under the auspices of the Max Planck Institute for Comparative Public Law and International Law under the direction of Professor Anne Peters (2021–) and Professor Rüdiger Wolfrum (2004–2020). 

Editor’s Note: A different entry under the title ‘Legal Positivism’, written in July 2011 by Frauke Lachenmann, appeared as part of the online Max Planck Encyclopedia of Public International Law until the publication of this entry in 2023. This new entry has been published at the same web address (URL) as the original entry. The original entry was also published in the 2012 print edition of the Encyclopedia (R Wolfrum (ed) The Max Planck Encyclopedia of Public International Law (OUP Oxford 2012) vol VI, 785–97).

A.  Notion

1  It has become a well-worn cliché to declare that the term ‘legal positivism’ is now so unclear as to be positively unhelpful. Yet the concept is frequently mentioned, arguments attributed to it are frequently discussed and critiqued, it was espoused by a number of prominent legal philosophers of the 19th and 20th century, most importantly Hans Kelsen and HLA Hart, and it continues to be used and discussed today. Hence, an explication is necessary before the many forms and uses of legal positivism, either generally or relating to international law, can be discussed. The word ‘positivism’ carries a wide range of meanings, not all of which are relevant in the present context; some can be excluded in order to achieve greater conceptual clarity. Legal positivism can be distinguished from general philosophical positivism, even though a number of important connections, particularly to the logical positivism of the Vienna Circle, exist. It can either be seen as a legal-philosophical school of thought or as a practice and tradition. International legal positivism can either be distinguished from general or domestic legal positivism—or taken as merely representing an application of general legal positivism to international law. It can either be seen as an approach relevant to all jurists or exclusively a theory of legal scholarship as academic endeavour. Some of these distinctions come into play below and will be discussed there.

2  Attempts have been made to define the minimum viable content of legal positivism either positively by genus and differentia, by family resemblance or at least negatively by uncovering myths about it (eg Gardner [2001]; d’Aspremont [2017]; Hall [2001] 272; Ott [1992] 19–31). An approximation of typical legal positivist positions is the following, even if limited to modern legal philosophical positivism and restricted in its expressive power, because positivist approaches will likely only adopt some of these arguments:

  • –  The creation or identification of legal rules or norms is based on ‘sources’, that is primarily on the form, rather than on the content of the rule.

  • –  Positive law is the primary or exclusive object of legal scholarship or practice with the word ‘positive’ either defined as a product of human creation through human acts of will, referring to the Latin word positus, or responding to the empirically given (‘positive’) social facts and reality of law.

  • –  Positivism is also identified by means of the belief that law can be separated from the realm of morals or ideology and can be defined or is valid independently of its moral value. This usually also involves separating the law in force (lex lata) from desirable law (lex ferenda).

  • –  Equally, positivism can be defined by its traditional antipathy to the idea of natural law or law of reason (Vernunftrecht) as a realm of absolute norms (Natural Law and Justice).

  • –  Some positivists espouse a form of value relativism: all values are relative and none are so superior simply by dint of their content or origin that they must exist a priori.

  • –  Some also espouse the non-reductivist is–ought dichotomy, the categorical distinction between the real world and the world of values or between statements about what ‘is’ and what ‘ought to be’.

3  In addition to typically espousing some form of some of the general legal positivist arguments above, particularly the sources, separability and anti-naturalist theses, classical international legal positivism is commonly said to hold the following, very closely inter-related ‘sovereigntist’ (Collins [2014] 36) positions, that is positions setting State sovereignty as absolute, pre-legal foundation for international law:

  • –  The original or sometimes exclusive subjects of international law are States; all other subjects derive their legal existence from the State.

  • –  The original and sometimes necessary source of international law is the consent of States (Sources of International Law).

  • –  When in doubt, international legal obligations must be presumed not to exist—the residual negative or Lotus principle (see Lotus, The).

  • –  International legal instruments, foremost treaties, must be interpreted so as to minimize or restrict the obligations of States parties: restrictive interpretation/interpretation in dubio mitius.

4  However, this type of list is of little use, because there is not much common ground between the different schools and because such lists imply that legal positivism is a purely legal-philosophical endeavour. In order to present a phenomenology of legal positivism as practices ‘in international law’, on the one hand, and to also do justice to complex and intricate modern positivist legal philosophical approaches, on the other, the discussion in the following will be bifurcated. Section B focuses on the arguments and practices developed specifically in international legal discourse. Section C portrays the most salient features of the two most important modern schools of legal philosophical positivism.

B.  The Tradition and Practice of International Legal Positivism

1.  Historical Development

5  The concept and relevance of ius positivum (Kuttner [1936])—human-made law, law made by human fiat as distinct from ius naturale and ius divinum—had long been recognized by legal scholarship, long before legal positivism emerged. However, there is approximate consensus on a canon of authors from the late 19th to the early 20th century hailing from Western Europe which can be identified as the core scholarly authorities of classical international legal positivism, with important forbears in the late 18th century such as Johann Jacob Moser (Moser [1777–1780]; see Verdross [1922/1923]); Emer de Vattel (de Vattel [1758]); and possibly the even earlier Thomas Hobbes (1588–1679), although his theory can probably not yet be described as legal positivism in the sense employed here. These include William Edward Hall (1835–1894) and his treatise (Hall [1880]); Georg Jellinek (1851–1911), particularly his Die rechtliche Natur der Staatenverträge (Jellinek [1880]); Lassa Oppenheim (1858–1919), particularly the first edition of his treatise (Oppenheim [1905]) and the programmatic article ‘The Science of International Law: Its Task and Method’ (Oppenheim [1908]); Heinrich Triepel (1868–1946) and his Völkerrecht und Landesrecht (Triepel [1899]); and the early Dioniso Anzilotti (1867–1950) of the first edition of Corso di diritto internazionale (Anzilotti [1912–1914]).

6  The traditional narrative of classical international legal positivism is one of a group of naïve late 19th-century voluntarists whose excesses were tamed by two waves of critique in scholarship in the interbellum years and in the late 20th century. Recent scholarship (eg Koskenniemi [2002]; von Bernstorff [2001]; Collins [2014]), while acknowledging that elements of this narrative are correct, has sought to paint a more differentiated picture of traditional international legal positivism and has sought to convey that the narrative of positivism’s opponents (eg Morgenthau [1940]) or of introductory texts cannot convey the complexity of this tradition. The precise content of classical legal positivism is also much more dependent on the author’s individual argument than is commonly acknowledged. Lastly, the natural focus of intellectual-historical research on scholarly writings (Literaturgeschichte; Oestmann [2014] 4) tends to skew the analysis of international legal positivism towards rational and abstract theoretical constructs which excludes the practice of positivism; it tends to under-report subconsciously adopted presumptions, biases and traditions (Kammerhofer [2021b] 97). It will therefore be advantageous to demonstrate the complexity of classical international legal positivist scholarship by way of a specific example. Oppenheim’s programmatic texts will be used (Oppenheim [1905] 3–25; Oppenheim [1908]), because among the core group of traditional positivists, his writings have been most widely researched and discussed (eg Schmoeckel [2000]; Kingsbury [2002]; García-Salmones [2013]) and because he exhibits an ideological world-view which is typical of traditional positivist approaches, differs markedly from legal philosophical positivism (see Section C below) and is variously critiqued in literature as apology of the Eurocentric status quo.

7  Oppenheim at points espouses typical sovereigntist arguments, for example:

Since the Law of Nations is based on the common consent of individual States, and not of individual human beings, States solely and exclusively are the subjects of International Law … Subjects of the rights and duties arising from the Law of Nations are States solely and exclusively (Oppenheim [1905] 18–19);

[I]nternational law is a law not above but between States; … there is no central authority above the sovereign States which could compel them to comply with the rules of international law or to submit their differences to a juridical decision … instead of taking the law in their own hands’ (Oppenheim [1908] 322).

These are, however, embedded in a consensualist foundation for all law: ‘law is a body of rules for human conduct within a community which by common consent of this community shall be enforced by external power’ (Oppenheim [1905] 8; emphasis deleted). This community can in international law only consist of States; its enforcement by an external power is provided not by a ‘central authority’, but by self-help by the wronged State and its allies (Oppenheim [1905] 13).

8  While States have to consent individually in order to be bound (Oppenheim [1908] 332–33), this does not mean that individual States can arbitrarily and at any time disavow their international legal obligations. If common consent

meant that all the individuals who are members of a community must at every moment of their existence expressly consent to every point of law, such common consent would never be a fact. … [Rather,] the express or tacit consent of such an overwhelming majority of the members that those who dissent are of no importance whatever (Oppenheim [1905] 15).

9  A State cannot ‘at some time or another declare that it will in future no longer submit to a certain recognised rule of the Law of Nations. The body of the rules of this law can be altered by common consent only, not by a unilateral declaration on the part of one State’ (Oppenheim [1905] 18). This is far removed from the traditional narrative about positivists as upholders of the individual State’s freedom and close to modern positivist conceptions of States being bound by empowerment rules of international law.

10  Another aspect of Oppenheim’s theory are his views on the tasks of international legal scholarship. ‘[T]he exposition of the existing recognized rules of international law’ are its ‘first and chief task … Whatever we think of the value of a recognized rule … we must first of all know whether it is really a recognized rule of law at all, and what are its commands’ (Oppenheim [1908] 314–15). Equally, ‘[i]f the positive is the right method of the science of international law, we must endeavor to get rid of bias of all kinds’ (Oppenheim [1908] 353). This is strongly reminiscent of Kelsen’s theory of legal scholarship (eg Kelsen [1960] 1, 72). However, the natural law basis of many traditional positivist approaches is also present: ‘The science of international law … is merely a means to certain ends outside itself [eg] peace among the nations and the governance of their intercourse by what … is right and just … [T]he task of the science stands in the service of these ends’ (Oppenheim [1908] 314). Consequently, scholars are required to be ‘imbued with the idealistic outlook’; those who do not possess ‘a deep-rooted faith in the progress of the nations towards peace and civilization’ are ‘not properly fit to work at the science of international law’ (Oppenheim [1908] 355).

2.  Current Practice

11  ‘Legal positivism’ is currently being practised in both scholarly and non-scholarly international legal discourse. It could even be called the most common, dominant or ‘default’ (Kammerhofer [2021b] 101–3) mode of arguing. Yet this practice or culture of positivism is not the same as a professional legal philosopher expounding a theory of legal positivism: practice is not a meta-level reflection, but, at best, a conscious application of a theory. There is also a question of how to define ‘positivism’ without referring to theoretical constructs. For the distinction between philosophical legal positivism and ‘positivism’ as a living practice, an analogy to Martti Koskenniemi’s ‘culture of formalism’ may be apposite. Conceptualizing a part of positivism as a culture which ‘is certainly not a substance or theory’ (Koskenniemi [2002] 508) may help to better understand what this practice is. Seeing it as culture also highlights the problem of expecting a high level of coherence and rationality from it and may aid in understanding what this form of positivism entails. Connected with this distinction is the question whether ‘legal positivism’ is properly only an approach to legal scholarship or something which all jurists do or ought to do.

12  Yet defining an undefined, because largely subconscious, practice of positivism poses a conundrum. What positions does this ‘actual practice of international legal positivism’ hold, how does one determine whether writer A or argument B is ‘positivist’ if not by reference to a definition? Is it advisable to use the lists of commonly held positions given in Section A above? Either the definition follows from an inductive move (some authors call themselves ‘positivist’, hence their positions are positivism) or from a deductive move (certain positions fulfil a priori criteria, whether or not they are declared as such). A definition from declarations is problematic, because the exceedingly rare self-declarations will likely only catch legal philosophical positivists and because most other declarations tend to be accusatory. Using an a priori definition involves an arbitrary decision and will likely proceed either from an unreflected received opinion or from a particular theoretical position. Understanding the practice of positivism is therefore best accomplished without a definition by means of an inductive process of collecting typical structures of arguments without necessarily heeding (self-)declarations.

13  An example can be found in the debate on self-defence relating to non-State armed groups. Judge Kooijmans, in his separate opinion in Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v Uganda) ([2005] ICJ Rep 168; Armed Activities on the Territory of the Congo Cases) relied on the ‘positivist’ argument that the Security Council, in resolutions 1368 and 1373, ‘recognizes the inherent right of individual or collective self-defence without making any reference to an armed attack by a State’; it ‘called acts of international terrorism, without any further qualification and without ascribing them to a particular State, a threat to international peace and security’ ([Separate Opinion of Judge Kooijmans] [2005] ICJ Rep 306 para. 28). Judge Simma, on the basis of an ‘enlightened positivism’ (Simma and Paulus [1999] 303), in the same judgment argued that the resolutions ‘cannot but be read as affirmations of the view that large-scale attacks by non-State actors can qualify as “armed attacks” within the meaning of Article 51’ ([Separate Opinion of Judge Simma] [2005] ICJ Rep 334 para. 11). Kooijmans saw the law changed on the basis primarily of the two resolutions and the State practice expressed therein. The positivism expressed in this reliance on expressions of practice is unconventional: the Council is neither authorized by positive international law to change the United Nations Charter nor to authoritatively determine whether an action (or a category of actions) is lawful under its Art. 51. If the argument is that an informal expression of State will within the Council can change the law or the way it should be interpreted, this would presuppose that pure practice without opinio iuris can override treaty rules.

14  When viewed from most modern general legal philosophical positivist approaches, the culture is not particularly positivist and can more precisely be described as a culture of orthodoxy (Kammerhofer [2021b] 97–103) rather than of positivism. This would also avoid the confusion connected with the continued use of the word ‘positivism’ for incommensurable concepts. That other culture is one of doing things in an orthodox manner, a mindset seeking to conform to the usual way in which things are done. This reading can explain the impression that many practices in international legal discourse which are labelled ‘positivist’ seem decidedly un-positivist. Rather than following positivist tenets, participants in this culture—largely subconsciously—tend to be orthodox, primarily in their adoption of traditional ways of doing things and in respect for conventionally accepted sources of (legal) authority: those argumentative practices which are better accepted by peers are viewed more favourably than those which are not. The socio-cultural phenomenon of ‘orthodoxy’ in international legal scholarship and practice incorporates at least three aspects: (1) It involves the privileging of the pronouncements of international judicial authorities, most prominently the International Court of Justice (ICJ), over the formal general sources of law. The deference to judicial authority is strong, except where a jurisprudence constante is seen as contrary to the development of State practice, as in the case of Kooijmans’ self-defence argument. It is based partly on peer acceptance and partly on the subconscious assumption that international tribunals will not err over a long time and on a vital question (d’Aspremont [2015]); (2) Orthodoxy also involves a significant amount of direct peer conformity vis-à-vis ‘epistemic’ authorities, both scholars and practitioners; acceptance by peers is seen as an important yardstick to the correctness of international legal arguments; (3) A certain pragmatism and accommodation, a trend towards the middle ground, both in terms of avoiding being seen as heterodox and of striving towards practicable and cosmopolitan solutions is a third observable phenomenon. The increasing integration of proportionality doctrine in international legal argument, seeking to ensure a balanced outcome, for example in international investment law, is an example of that sense of accommodation. When this kind of pragmatism involves instrumentalism, when legal arguments tend primarily to be used in order to support a cause, orthodoxy’s distance to legal philosophical positivism becomes greatest.

15  If this a-theoretical practice were nonetheless reconstructed as legal philosophical project, the result might be that in some areas, currently practised international legal positivism is closer to certain statist traditions of natural law thinking than modern legal philosophical positivism: State will is law-determinative and States are the original subjects of law by a priori necessity, rather than by the a posteriori happenstance of positive law.

C.  Modern Legal Philosophical Positivism and International Law

16  The tradition and practice of positivism in international law (Section B above) can be contrasted with legal philosophical approaches to law in general. These are conscious endeavours to theorize the law which are in principle based on a commitment to coherence, rather than on pragmatism or tradition. They also tend to argue that international law and its scholarship are merely particular examples or applications of generally applicable mechanisms and epistemic enterprises, respectively. The second half of the 20th century saw the consolidation of legal positivist approaches into two major families, based on Hans Kelsen’s and HLA Hart’s works. Both remain vibrant and popular schools of thought in the 21st century, with at least four generations of thinkers having engaged in discussing, applying, developing and modifying their respective founder’s original ideas. The taxonomy of the family ‘legal positivism’ is such that it contains a great number of species, but that the vast majority of what is being propounded today can be traced to Hart or Kelsen: in effect, only those two genera remain. There is an argument to be made that those two approaches are based on incomparable and incompatible metatheoretical foundations and that it makes little sense to speak of both belonging to a single genus (Kammerhofer [2016] 426). Finally, particularly Hart’s own application of his theory to international law is seen as problematic; a new generation of scholars writing on both Hart and Kelsen have engaged in re-applications of their approaches which are based on the idea of establishing, as they see it, a closer coherence with the theoretical superstructure.

1.  Kelsen and the Pure Theory of Law

(a)  Legal Philosophical Approach

17  From 1920, Kelsen called his approach Reine Rechtslehre, a Pure Theory of Law (Kelsen [1920] i). The adjective ‘pure’ refers to ‘theory’, not ‘law’, and it operates both as a legal theory proper—how law and norms work—and as a Rechtswissenschaftstheorie (Lippold [1989] 29–30), a ‘philosophy of legal science’—how legal scholarship is possible as proper scholarship in the Germanic sense of Wissenschaft. It is modelled to some extent on the ethos prevailing in the natural sciences, a detached, objective, exact and methodical discovery of what is ‘out there in the world’. However, legal scholarship has a different object to the natural sciences and its theory must respect and reflect the specific manner in which the law functions (Eigengesetzlichkeit) (Kelsen [1960] iii). For Kelsen, this requires describing the law in force only and excludes a methodological reduction of legal scholarship to a social science as well as any reliance on meta-legal values such as political ideologies, morality or natural law. This ‘two front war’ (Dreier [1986] 27: ‘doppelte Frontstellung’) against both popular approaches—traditional naturalism based on teleological or ideological world-views as well as the then-new socio-scientistic reductivism—in combination with its ascetic programme and ethos has caused great consternation and puzzlement as well as a significant amount of criticism, not all of it based on rational arguments. It is also clear that on this account, ‘positivism’ is aimed at legal scholars; neither practitioners nor even the law itself can be ‘positivist’, and talk of ‘positivist’ sources of law is seen as nonsensical.

18  A properly legal scholarship which respects law’s Eigengesetzlichkeit will combine its nature as an ideal with the reality of its creation through actual human willing. Hence, the Pure Theory can fairly be described as normativist positivism. Its normativism proceeds from the assumption that law is a subspecies of normative orders which, in turn, contain norms, an ought. This is typically, but not exclusively, a prescription or prohibition of specific human behaviour (Kelsen [1979] 1–7). The validity of law, in turn, has no ‘ultimate’ foundation and the highly controversial Grundnorm is only a nomo-epistemic tool to enable the perception of norms as Ought. All human beings necessarily presuppose a Grundnorm when they perceive norms as norms; it is the only way in which humans can conceive of norms.

19  The Pure Theory’s positivism, in contrast, draws closely on the Latin original word positus: norms set or put into the world by human willing:

Eine durch einen in der Seinswirklichkeit stattfindenden Willensakt gesetzte Norm ist eine positive Norm. Vom Standpunkt eines Moral- oder Rechtspositivismus kommen als Gegenstand der Erkenntnis nur positive, d.h. durch Willensakte, und zwar durch menschliche Willensakte, gesetzte Normen in Betracht. … In diesem—durch menschliche Akte—Gesetzt-Sein … liegt die Positivität der Moral und des Rechts. … [D]ie Seins-Tatsache… des Gesetzt-Werdens [ist eine] Bedingung… der Geltung einer Norm, aber nicht diese Geltung selbst.

A norm which was created [set] by [or: through the use of] an act of will taking place in reality is a positive norm. For a moral or legal positivism, only positive norms, i.e. such norms as are created by human acts of will, are considered as possible objects of cognition. … The positivity of morals and law lies … in this act of creation by human acts. … [T]he Is-Fact… of Being-Enacted [is a] condition… for the validity of a norm, but not validity itself (Kelsen [1979] 4, 114).

20  This concept clashes with the traditional international legal positivist idea that State consent or State will is a necessary law-creating fact in international law: for the Pure Theory, contingent rule-creating rules, rather than arguments from necessity determine law-creation. The creation of a norm requires both a norm empowering the creation of further norms and an actual act of will by a person or persons creating the norm, as specified in the empowerment norm.

21  The relationship between two norms created by subsuming the creation of a norm under the conditions of an empowerment norm also allows for an analysis of the structure of legal orders (Merkl [1931] 252) based on a formal criterion. The validity-relationship is seen as the foundation for the dynamism of legal orders:

Da … eine Norm darum gilt, weil und sofern sie auf eine bestimmte, das heißt durch eine andere Norm bestimmte Weise erzeugt wurde, stellt diese den unmittelbaren Geltungsgrund für jene dar.

Since a norm … is valid if and when it was created in a certain fashion determined by another norm, the second norm is the immediate source of validity of the first norm (Kelsen [1960] 228).

Since this relationship concerns the very ‘existence’ of norms (ie their validity), it is, on a normativist view, the only necessary form of relationship; all others are contingent.

(b)  Recent Application to International Law

22  In contrast to the Hartian school, a number of the original members of the Vienna School of Jurisprudence, the group around Kelsen, were prominent international legal scholars in their own right, such as Kelsen himself, Joseph L Kunz, and Alfred Verdross (Kunz [1934]). However, it can be argued that recent applications of the Pure Theory to international law might sometimes be closer to its theoretical core tenets than the legal-doctrinal writings of the original members. Also, because using recent writings is unavoidable for Hartian positivism, a comparison between two recent offerings may yield more closely matched results.

23  A number of scholars have discussed the import of Kelsen’s international law theory, foremost Jochen von Bernstorff (von Bernstorff [2001]; see also Rub [1995] and the contributions in EJIL Symposium [1998]; Walter Jabloner and Zeleny [2004]); few have tried to apply the Pure Theory of Law to international law and its doctrinal scholarship (eg Gragl [2018]; Kammerhofer [2010]). Jörg Kammerhofer in particular has applied the Pure Theory of Law’s insights to international legal scholarship. He argues that ostensibly ‘doctrinal’ arguments are dependent on legal-theoretical positions, that an integrated analysis of both is unavoidable and that the Pure Theory of Law is the preferrable theoretical approach, one closest to conventional legal analysis while avoiding most of its inconsistencies. As a re-application of the Pure Theory, this will also mean that certain elements of Kelsen’s own arguments have to be reformulated, for example the Zwangsnormpostulat (‘coercive order paradigm’), according to which law is necessarily a coercive order, an order structured by orders to officials to apply sanctions. Kammerhofer believes that Kelsen’s re-interpretation of international law under that paradigm skews the result and should be avoided: law as a coercive order for him is merely an a posteriori ‘empirical’ classification of certain normative orders as ‘law’ (Kammerhofer [2009] 227–33, 236–40).

24  Kammerhofer’s main focus is the proper role and function of international legal scholarship and the structural analysis of the international legal order. The former involves a critique of ‘improper’ practices and a description of the core business of (international) legal scholarship. An example of the pathology is the distinction in international legal scholarship between ‘orthodox generalists’, seeking pragmatic and diplomatic consensus solutions, and ‘political activists’, consciously instrumentalizing scholarship to achieve political ends (eg Kammerhofer [2012] 139–54). The constructive element involves showing that proper scholarship involves both a macro-structural analysis of the law—relationship between norms and sources—and a micro-structural analysis—interpretation as determination of the frame of possible meanings (eg Kammerhofer [2022b]).

25  Kammerhofer also engages in structural analysis, which involves questioning the assumptions behind orthodox legal doctrines. In his 2021 book International Investment Law and Legal Theory: Expropriation and the Fragmentation of Sources, he analyses whether general regulatory measures taken by the host State are excepted from the reach of indirect expropriation prohibitions in investment agreements (Expropriation, Indirect; Expropriation and Nationalization; Investments, International Protection). One popular argument is that ‘indirect expropriation’ incorporates customary international law (which excludes regulatory measures) and that this incorporation happens by default; proof is required for a divergence of custom and treaty (eg Newcombe and Paradell [2009] 339). On his account, while treaty-makers can incorporate the content of customary law, this can only happen by positive regulation, particularly if treaty law is an inter partes contracting-out from ius dispositivum customary rules. If lex specialis is to be conceptually possible, contracting out must not be made virtually impossible. That ‘States generally seek to incorporate in their BITs the “customary international law standards for expropriation”’ (McLachlan Shore and Weiniger [2017] 369) does not mean that the content of treaty law gains any significant specificity.

2.  Hart and the Hartians

(a)  Legal Philosophical Approach

26  HLA Hart was born later than Hans Kelsen, his philosophical background in the Oxford school of ordinary language philosophy is perceived as more ‘modern’ than Kelsen’s sometime reliance on Kantian and neo-Kantian arguments and the approach founded by Hart certainly shows more global vibrancy today than Kelsen’s. Yet in some respects, Hart is closer to the Anglo-Saxon forbears of legal positivism such as Jeremy Bentham and John Austin than Kelsen is to the German Gesetzespositivismus of the 19th century.

27  In contrast to the Pure Theory of Law, Hartian positivism is decidedly social or sociological; its philosophy is decidedly analytical and linguistic. The question Hart asks is not ‘What is the basis for the validity of law?’—founding normativity, for example, is a non-problem for Hart (Toh [2015] 348–53)—but ‘When can we properly speak of “law”?’ (see Hart [1983]; von der Pfordten [2012] 38, 42). The answer, according to most Hartians, is a social one, prompted inter alia by the programmatic statement in the preface to The Concept of Law that it is ‘an essay in descriptive sociology’ (Hart [1961/2012] vi; see also Green [2012] xv: ‘Law is a social construction’). The anti-metaphysical affect, which Hart to some extent shared with Alf Ross, disallows idealistic ontology and radically changes the nature of his legal epistemology (see Möllers [2011] 380). It is crucial to understand, however, that Hart did not intend to advocate a form of legal realism by seeking to reduce the normative significance of law to behavioural or natural facts; indeed, this applies in particular to the much-misunderstood (Toh [2015] 340–45) distinction between internal and external points of view and the attendant ascription of a ‘practice theory of rules’ (Raz [1975/1999] 49–58) to Hart.

28  For Hart, law is a system of rules, rather than independent social rules. It is characterized by the union of primary and secondary rules: primary rules are duty-imposing, under which ‘human beings are required to do or abstain from certain actions’ (Hart [1961/2012] 81), whereas (at least some kinds of) secondary rules are power-conferring. Hart discusses three types of secondary rules: rules of change, rules of adjudication and the rule of recognition (Hart [1961/2012] 91–99). Legal systems contain both primary and secondary rules, mere social rules usually do not. The simple rules and the rule of recognition of a legal system merely exist (Hart [1961/2012] 234), rules of a legal system are valid within the system—this is a task for the rule of recognition:

This will specify some feature or features possession of which by a suggested rule is taken as a conclusive affirmative indication that it is a rule of the group to be supported by the social pressure it exerts. … No such question can arise as to the validity of the very rule of recognition …; it … is simply accepted as appropriate for use in this way (Hart [1961/2012] 94, 109).

The rule of recognition is carried by acceptance, but this is a complex and differentiated rule:

A legal system exists or prevails in a community if some powerful subset of the members of the community … ‘officials’ … accept the secondary rules …, and the rest of the community at least follow the norms that are valid according to the rule of recognition prevailing in that community. A person accepts a norm, or takes an ‘internal point of view’ …, when he believes there to be reasons to follow it. And the psychological state of acceptance is constituted by the person’s dispositions to regulate his own conduct in accordance with the norm, to justify his own and others’ conduct by appeals to that norm, and to criticize his own and others’ deviance by appeals to that norm (Toh [2013] 460).

(b)  Recent Application to International Law

29  Notoriously, Hart did not regard international law as fulfilling the criteria set out above for being able to speak of a legal system: ‘the rules [of international law] which are in fact operative constitute not a system but a set of rules … the analogy [to municipal law] is one of content not of form’ (Hart [1961/2012] 236, 237). A number of international legal scholars have attempted to ‘rectify’ this situation: either by calling interpretations which see Hart as sceptical of international law unfair or by reinterpreting or modifying the Hartian theory to accommodate international law better (eg van Hoof [1983]; Beckett [2008]; Payandeh [2010]; d’Aspremont [2011]; Bisogni [2021]).

30  Until about 2015, Jean d’Aspremont was the premier neo-Hartian international legal theorist. While his more recent writings have taken a turn towards critical legal scholarship, the writings from his Hartian phase remain the most prominent and consistent application of Hart to international legal scholarship even today. In his 2011 book Formalism and the Sources of International Law, d’Aspremont seeks to describe how international legal rules can be ‘ascertained’ in a formal manner. He ascribes to Hart a version of the ‘social thesis’: ‘formal law-ascertainment derived from social practice … inferring the meaning of the standard pedigree of rules derived from the practice of law-applying authorities’ (d’Aspremont [2011] 15) and puts the social practice approach at the heart of his efforts. In so doing, he adopts and adapts particularly strongly socio-realist readings of Hart’s theory such as Brian Tamanaha’s, seeking to rectify Hart’s perceived reluctance vis-à-vis international law. He does so by first introducing ‘communitarian semantics’ and by then expanding the meaning of ‘law-applying authority’.

31  The ascertainment of law by formal criteria is possible because those whose voice matters use these criteria reasonably alike: ‘the meaning of law-ascertainment criteria originates in the convergences of the practice of law-applying authorities’ (d’Aspremont [2011] 197), which must include a ‘shared feeling of applying the same criteria’ (d’Aspremont [2011] 201). Communitarian semantics, then, is practice plus feeling, remarkably reminiscent of main-stream conceptions of customary international law-creation of practice plus opinio. The agents of this communitarian semantics, in turn, are not merely Hart’s ‘officials’; d’Aspremont expands the concept to all those who, in Tamanaha’s words, ‘as a matter of social practice, members of the group (including legal officials themselves) identify and treat as “legal” officials’ (Tamanaha [2001] 142). D’Aspremont argues that, because ‘other “social actors” participate in the practice of law-ascertainment’, this is reason enough that these ‘should be taken into account in the determination of the communitarian semantics constitutive of the meaning of law-ascertainment criteria’ (d’Aspremont [2011] 204). Because this argument is ostensibly about ascertainment, viz identification, rather than law-making (see, however, Kammerhofer [2022a] 17–20), his analysis is not restricted to law-making authorities such as States. Scholars, however, who generate significant amounts of ascertainment-talk, are reduced to grammarians of law-ascertainment (d’Aspremont [2011] 209–11). D’Aspremont’s neo-Hartian positivism comes very close to some streams of legal realism, because it relies on social practices and external analysis of belief-states of participants. Hart clearly saw the danger in conflating the two approaches (Hart [1959]) and might have resisted ‘sociologised’ readings of his theory, because they are ultimately susceptible to a critique of reductivism (Kammerhofer [2016] 418–25).

D.  Evaluation

32  Debates about legal positivism, whether general or international, whether philosophical or as a practice, are marked by confusion, misunderstanding and quite a bit of malice. Legal positivists themselves are to blame for this just as much as their detractors; even non-committed intellectual historians risk being drawn into the maelstrom of straw-men and malicious readings which the very emotiveness of the issues discussed à propos this family of approaches to law and legal scholarship has engendered. This has been the case throughout the history of thinking about politics, the State and law, but it sharpened when (proto-)legal positivists first challenged the natural law default position.

33  It is easy to understand that positivists, seeing the development of natural sciences as an emancipation from speculative natural philosophy, would want to emulate that move and would sharply criticize natural law’s implicit argument from necessity, ostensibly critical of unjust law but in effect always a force to stabilize the status quo. How dare natural lawyers, they might ask, hide their personal preferences as expressions of human nature or of reason when there is a way to objectively, ‘scientifically’, analyse the laws humans have created? It is equally easy to understand that the new natural lawyers of the 20th century, seeing so much injustice done under the guise of positivism, would sharply criticize positivism’s implicit pandering to the power of the strong, ostensibly objective but more often a tool to justify immoral and unjust laws. How dare positivists, they might ask, hide behind the positive law, refusing to engage in the essential debates about the true foundation, the justness and legitimacy of the law?

34  The reception of legal positivism has become even more complicated with the increasing popularity of critical approaches to law. In general legal scholarship (eg Vinx [2007]) as in international legal theoretical writings (eg García-Salmones [2013]; Koskenniemi [2002]), positivism has been described as a political project, a project which consciously or subconsciously pursues a particular ideology, but hides that fact under the rhetoric of an ostensibly objective, neutral scholarly ideal. This critique has some merit: as Section B above has shown, political ideologies are pursued which are labelled as ‘positivism’. However, this is a qualitatively different type of critique than natural lawyers or other legal philosophers would level, which weakens, rather than strengthens the appeal of such radical approaches.

35  Some more radical critics employ an argument about the necessity of a political superstructure (Überbau): all non-material choices are inherently political. This negates the possibility of non-political arguments and choices, in the present case that positivism (or other approaches) could be epistemological theories, part of the philosophy of science. This amounts to a foisting of premises: if one were to admit the political project argument, one would implicitly have to accept that the correct way to discuss scholarship is political and therefore based on ideological positions. Accepting the Pure Theory, in particular, as a political project would mean that Kelsen and his circle subconsciously sabotaged the most fundamental axiom of that theory, the ‘purity’ of legal scholarship as an epistemic endeavour, which is not commensurate with a coherent reading of that approach. Far from being a subconscious part of the Pure Theory, it has consciously and extensively reflected on, argued about, and critiqued the role of ideology in legal scholarship. Pure theorists, rather than subconsciously repressing their ideology, have propounded an epistemological argument that ideology is not and should not be all-pervading in scholarship. Believing in the radical political project argument would mean that scholarly-epistemological arguments are nullified by an ideology—the ideology that ideology reigns supreme.

36  Just as ‘positivism’ is obviously problematic and utterly muddled, so it is obviously ubiquitous and vital in the sense that positivist arguments are unlikely to disappear any time soon. Hartian or Kelsenian theories may or may not remain popular in international legal scholarship, but at least the practice of international legal positivism, the reliance on typical positivist arguments and positions by doctrinal scholars and practitioners, is as ineradicable as the concept of law based on human fiat.

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