- 1 From a historical-biographical perspective, much is known. For example, while living in Vienna, Kel (...)
- 2 Providing a complete and consistent characterization of the pure theory of law presents several cha (...)
- 3 Providing a complete and coherent characterization of logical positivism also presents challenges. (...)
1The subject of this article is the relationship between Kelsen and the Vienna Circle. It is important to make clear from the outset, however, that I will not address this relationship from a historical or biographical point of view.1 Instead, my focus will be on the theoretical relationship between Kelsen's philosophy of legal science, on the one hand, and the Vienna Circle’s general philosophy of science, on the other. In other words, this paper seeks to provide an inter-theoretical comparison between the pure theory of law2 and logical positivism.3
- 4 The only studies that focused exclusively on this question were prepared for a symposium held at th (...)
2I intend to explore the following question: Is the pure theory of law philosophically closer to logical positivism than is commonly assumed? Or, as traditionally held, should it be regarded as a significantly distant approach? Although this question is by no means new – as it is framed now, it could have been formulated nearly a century ago! – it has received surprisingly little attention in the relevant literature.4
3Even more striking is that the limited existing literature shows significant disagreement among the most prominent experts on how this question should be answered. Some specialists, such as Robert Walter, one of the most distinguished scholars of Kelsen's thought, argue that the pure theory of law and logical positivism can indeed be seen as closely related approaches. He states:
- 5 Walter is not alone in this view. Friedrich Stadler, a leading expert on the history and philosophy (...)
Although the position of the Pure Theory of Law cannot rely on the main positions of the Vienna Circle ... important parallels are evident. One could say that the Pure Theory of Law is philosophically more connected to the Vienna Circle than separated from it (Walter 2001: 17; translation mine, author´s italics).5
- 6 Stadler 2001: xvii; translation mine.
4This idea, which emphasizes the affinity between the pure theory of law and logical positivism, seems to be reinforced by a significant biographical fact: Kelsen himself seems to understand it this way. In a letter to Otto Neurath, he explicitly states: “The parallels between my Pure Theory of Law and Carnap's philosophy are indeed striking”.6
5However, other experts, as renowned as Walter, hold the opposite view: that the pure theory of law and logical positivism are philosophically distant. A key example comes from Clemens Jabloner, who declares:
It seems natural to link the legal positivism of the Pure Theory of Law with the Vienna Circle's neopositivism. But ... it should first be noted that there was an unbridgeable rift between neopositivism and the Pure Theory of Law (Jabloner 1998: 378-379; italics added).
6The main goal of this article is to settle this debate. To achieve this, I divide my exposition into three parts. In the first section, I explain why the pure theory of law and logical positivism should be definitively regarded as philosophically distant approaches. I argue that their theoretical gap stems from three basic disagreements at the level of the philosophy of science; specifically, they differ on: i) the foundation of scientific knowledge, ii) the meaning of scientific sentences and iii) the nature of social sciences. In the second part, I contend that the traits of Kelsen's thought often cited to bring his theory closer to that of the Vienna Circle – particularly, his “anti-metaphysical” inclination and his conception of the history of “causality” – are insufficient to support such a claim, since they either reflect a mere terminological coincidence or a peripheral similarity. In the third part, I highlight an additional theoretical benefit that stems from this inter-theoretical comparison. Specifically, I show how comparing Kelsen's philosophy of legal science with the Vienna Circle's general philosophy of science is key to deeply understanding the nature of the criticisms that the pure theory of law received from other legal positivists during the 20th century. Finally, I provide a brief summary to close.
7The first disagreement between the pure theory of law and logical positivism lies in their respective understanding of the foundation of scientific knowledge.
- 7 This manifesto was written in honour of Moritz Schlick and presented at the “Congress on the Episte (...)
8The logical positivists adopted an empiricist view. This means that, according to them, knowledge of the world cannot be based on reason, but only on experience, i.e., what can be perceived through the senses. Thus, in their manifesto published in 1929 and titled Wissenschaftliche Weltauffassung: Der Wiener Kreis,7 they stated the following:
... The scientific world-conception ... is empiricist ...: there is knowledge only from experience, which rests on what is immediately given. This sets the limits for the content of legitimate science (Carnap, Neurath & Hahn 1973 [1929]: 309; author´s italics).
9However, it is important to clarify that this empiricist orientation was not expressed through an explicit philosophical defence, since doing so would have meant entering a territory they specifically wanted to avoid: metaphysics. Instead, their empiricist stance emerged through two main indirect ways.
- 8 The “protocol language” is quite similar to what we now refer to as “basic statements” or “observat (...)
- 9 Carnap, Neurath & Hahn 1973 [1929]: 309.
10One way their empiricism was expressed was through a particular view of the language of empirical science. Broadly speaking, this view holds that the language of empirical science can be translated into one that is as closely tied to experience as possible, which they initially called “protocol language”.8 This idea was already included in the previously mentioned manifesto. There, for example, it is stated: “... the meaning of every statement of science must be statable by reduction to a statement about the given”.9
- 10 Ayer 1959: 17.
- 11 Indeed, if the “protocol language” refers to sensory data that are the content of a subject's menta (...)
- 12 Moulines 2011: 54.
- 13 Unlike “phenomenism”, “physicalism” allows for the sentences using this language to be intersubject (...)
11However, beyond their consensus on this general postulate, the members of the Vienna Circle engaged in intense internal debate about the nature of this “protocol language”.10 At first, primarily influenced by Moritz Schlick and Rudolf Carnap, a conception known as “phenomenism” prevailed. According to “phenomenism”, the “protocol language” refers to sensory data situated in the mind of a particular subject. However, this initial conception quickly lost popularity once it became clear that it suffers from a central methodological problem: it leads to solipsism.11 As a result, and due to Otto Neurath's insistence,12 a second conception known as “physicalism” eventually triumphed. The central idea of “physicalism” is that the “protocol language” refers not to the mental contents of a subject but to physical entities located in time and space as well as properties that are directly verifiable through the senses.13
12The second indirect way in which logical positivism expressed its empiricism was through a strong anti-metaphysical inclination. One of the motives – though neither the only nor the most important, as we will see – that the members of the Vienna Circle rejected from traditional philosophy was that they regarded it as a “merely speculative” practice. For instance, in the same manifesto they declare:
The ... basic error of metaphysics consists in the notion that thinking can either lead to knowledge out of its own resources without using any empirical material ... (Carnap, Neurath & Hahn 1973 [1929]: 308; author´s italics).
13And, according to them, this is a mistake into which fall:
... not only metaphysics in the proper, classical sense of the word, especially scholastic metaphysics and that of the systems of German idealism, but also the hidden metaphysics of Kantian and modern apriorism (Carnap, Neurath & Hahn 1973 [1929]: 308; author´s italics).
- 14 Their main “enemies” were primarily Hegel and Heidegger.
- 15 This rejection also encompasses Neo-Kantianism, as the quotation demonstrates, since they oppose al (...)
14As can be inferred from this last quote, logical positivism equally rejects both openly metaphysical philosophical systems14 and those, like Immanuel Kant's,15 that attempt to avoid metaphysics – at least in the purely speculative form that Kant referred to as “dogmatic”. In particular, their rejection of Kantian philosophy was motivated not only by Kant's controversial view on the existence of “synthetic a priori judgments”, but also by more fundamental aspects of his epistemology; namely, his “transcendental idealist” conception. Thus, in his Critique of Pure Reason (1928 [1781]), Kant raises the following question: How is it possible to have “certain” and “solid” knowledge —such as that found in Newtonian physics? His answer to this question is that knowledge of this nature cannot be founded upon mere sensory perception. Rather, it is only possible if the subject epistemologically constructs the object of his knowledge, i.e., if he connects the impressions received through the senses with the help of certain “forms of sensibility”, such as the concepts of time and space, and certain “categories” or “pure concepts of the understanding”, such as the notions of substance and accident, or cause and effect. And, according to Kant, all these forms and categories are a priori, meaning that they are not derived from experience but from reason; in other words, they are introduced into the object of knowledge by the subject.
- 16 This is something that Kelsen explicitly acknowledges in his self-presentation from 1927. There, he (...)
- 17 Kelsen 1967 [1960]: 5.
15The pure theory of law adopts this latter conception: the “transcendental idealist” one.16 Kelsen's starting point is the following question: How is purely legal knowledge possible? His basic assumption is that this knowledge cannot be grounded in mere sensory perception, since sensory perception does not allow one to distinguish between a prescription of any kind and a legal norm – in other words, to differentiate between the command of a robber and that of a tax official. Thus, according to Kelsen, what sets legal norms apart from other prescriptions is their “validity” or “binding force”.17 And, in his own words, this is something that:
... is not immediately perceptible by the senses —such as, for instance, that colour, hardness, weight, or other physical properties of an object can be perceived (Kelsen 1967 [1960]: 3).
- 18 Indeed, in his Théorie pure du droit, Kelsen states: “Undoubtedly, it can be considered that the no (...)
- 19 Bulygin, 2021 [1980]: 398.
16For this reason, Kelsen holds that legal science must epistemologically construct its object as a condition for purely legal knowledge.18 In other words, it must link certain prescriptions to “validity”, thereby transforming them into legal norms. In Kelsen´s opinion, the only way legal science can accomplish this task is in the manner of Kant: through a specific “category” or “pure concept of the understanding”, which as Bulygin remarks with some irony,19 Kant seemingly forgot to mention, and which Kelsen famously called the “basic norm” (Grundnorm). He explicitly expresses this idea when he states:
Insofar as only the presupposition of the basic norm makes it possible to interpret [prescription] acts ... as valid legal norms, the basic norm as represented by the science of law may be characterized as the transcendental-logical condition of this interpretation, if it is permissible to use by analogy a concept of Kant's epistemology (Kelsen 1967 [1960]: 202).
- 20 Kelsen 1967 [1960]: 204.
17And, just as in Kant, this specific “category” – the “basic norm” – is a priori. This means that it is not grounded in experience, but in reason. In other words, it is introduced to the object of knowledge by the subject – in this case, the legal scholar. This explains why Kelsen says that the “basic norm” “... can only be the meaning of an act of thinking”.20
18As can be noted, there is a clear contrast here between the pure theory of law and logical positivism. One critique that members of the Vienna Circle would likely raise against the pure theory of law is that it is over-inclusive – i.e., it incorporates elements that, in their view, should not be part of legal science. Basically, they would argue that by introducing the notion of “basic norm”, along with all the other concepts that depend on it, such as “validity” or “binding force”, he is infecting legal science with metaphysics.
19And, according to their view, Kelsen would have only two ways to avoid falling into metaphysics: either translating the concept of the “basic norm” into “physicalist language” – i.e., reducing it to concepts that refer to physical entities and directly verifiable properties – or abandoning it outright. However, as is well known, these are steps that Kelsen was never willing to take. One of the key ideas he repeatedly emphasizes is that legal science cannot dispense with this “category” because without it, it would be unable to purify its object – the law – from nature; in other words, it would be unable to distinguish between an ordinary prescription and a legal norm – or between the command of a robber and that of a tax officer.
20But that’s not all: the members of the Vienna Circle would argue not only that the pure theory of law is over-inclusive, but that it is also under-inclusive in that it excludes elements that, in their view, should be part of legal science. This is primarily due to the content and function that Kelsen assigns to his “basic norm”. Let me explain why.
- 21 Kelsen 1967 [1960]: 50.
- 22 It should be clarified that when Kelsen refers to “morality” in this context, he is not talking abo (...)
- 23 Kelsen is very clear on this point. In one passage from the Pure Theory of Law, he states: “... onl (...)
21In Kelsen’s view, the “basic norm” of a national legal order has the following content: “Coercion ... ought to be exercised in the manner and under the conditions determined by the historically first constitution”.21 Kelsen assigns it this content for a well-known reason: in his view, the only way legal science can construct its object of knowledge – the law – as something “purified” from morality22 is by focusing not on its content or source, but on the characteristic way in which it motivates behaviour; in other words, by conceiving the law as a “coercive order”.23
- 24 Kelsen 1967 [1960]: 60.
- 25 Kelsen 1967 [1960]: 52. This idea sparked an important debate within general jurisprudence concerni (...)
- 26 In this regard, Kelsen states explicitly: “By the word ‘validity’ we designate the specific existen (...)
- 27 That's why Carlos Nino correctly asserts: “... it is not surprising that under the Kantian outlook (...)
22From this definition, Kelsen derives a rather curious conclusion. For him, all legal norms establish coercive acts as sanctions – or form part of the antecedent of such a norm.24 Of course, the question that many scholars have raised is: What happens if a legal authority prescribes something that neither establishes a coercive sanction nor forms part of the antecedent of a norm that does? Kelsen’s response is: “In this case ... the norm ... cannot be interpreted as a legal norm, but must be regarded as legally irrelevant”.25 As can be seen, Kelsen essentially says that if legal scholars encounter a norm issued by a legal authority that lacks a coercive sanction – and is not linked to a norm that establishes one –, they must consider it invalid or, what is the same in Kelsen, as non-existent.26 This means that the legal scholar must exclude this norm when constructing their object of knowledge; they must keep it outside their “field of view”.27
- 28 Kelsen 1967 [1960]: 205.
23A similar idea arises from one of the functions that Kelsen assigns to his “basic norm”. On his view, the “basic norm” not only transforms certain prescriptions into legal norms, but also imposes unity on a multiplicity of norms. Put differently, it turns a set of norms into a system.28 As he explains:
It is further true that, according to Kant's epistemology, the science of law as cognition of the law, like any cognition, has constitutive character—it 'creates' its object insofar as it comprehends the object as a meaningful whole. Just as the chaos of sensual perceptions becomes a cosmos, that is, 'nature' as a unified system, through the cognition of natural science, so the multitude of general and individual legal norms, created by the legal organs, becomes a unitary system ... through the science of law (Kelsen 1967 [1960]: 72).
- 29 It is worth noting that in his posthumous work Allgemeine Theorie der Normen (1979), Kelsen ultimat (...)
24From this idea, Kelsen draws another curious conclusion: that legal norms cannot contradict each other.29 This, once again, raises the following question among legal scholars: What happens if a legal authority enacts conflicting norms – and there is no interpretive method to resolve the normative conflict? Kelsen's response is similar to his answer regarding norms that lack coercive sanctions:
To be sure, it is undeniable that legal organs may create conflicting norms .... [Given this…] the legislator creates something meaningless; ... and therefore ... no ... valid legal norm is present ... (Kelsen 1967 [1960]: 207).
25Again, what Kelsen is suggesting is that if legal scholars encounter two contradictory norms issued by legal authorities – and find no admissible way to resolve the conflict – they must consider both invalid or non-existent, thereby excluding them when constructing their object of knowledge.
- 30 In this regard, it is very illustrative that in the manifesto states that, “For us, something is 'r (...)
26It should now be clear why the logical positivists would consider the pure theory of law to be under-inclusive: for them, it would be unacceptable for certain prescriptions – which anyone would agree form part of “legal experience” –30 to be deliberately excluded from the object of legal science simply because they do not fit with the content or function of that a priori “category” called “basic norm”.
- 31 Carnap, Neurath & Hahn 1973 [1929]: 308.
27The second disagreement between the pure theory of law and logical positivism is related to the meaning of scientific sentences. According to logical positivism, science consists exclusively of sentences with cognitive meaning – i.e., that express propositions capable of being true or false. And there are only two types of propositions: “... empirical statements about things of all kinds, and analytic statements of logic and mathematics”.31 In other words, for the logical positivists, science is composed solely of either analytical or synthetic propositions. The former refers to tautologies or contradictions, and their truth value can be determined a priori – i.e., by considering only the meaning of their terms. In contrast, synthetic propositions refer to events or states of affairs in the world, and their truth value can only be determined a posteriori – i.e., by appealing to experience. This implies that, according to them, there is no place in science for that third type of proposition that Kant called “synthetic a priori judgments”. Such statements simply do not exist.
- 32 It should be noted that they embraced “logicism”, primarily advocated by Gottlob Frege and Bertrand (...)
- 33 In this regard, they differed from other, more radical empiricist authors. For instance, J. S. Mill (...)
28On this basis, the logical positivists distinguished between two types of scientific disciplines, according to the kinds of propositions they contain: formal sciences, on the one hand, and empirical sciences, on the other. Formal sciences – such as logic or mathematics –32 are composed exclusively of analytical propositions and, consequently, do not provide any information about the world.33 In contrast, empirical sciences – such as physics, biology, or sociology –, which do aim to inform about the world, contain propositions of both types, but primarily synthetic ones.
- 34 However, it is worth mentioning that this criterion of meaning has changed over time. They quickly (...)
- 35 This definition aims to succinctly capture what the logical positivists referred to as “verifiabili (...)
29Furthermore, another point the members of the Vienna Circle upheld – at least in its early stages – was that synthetic propositions are subject to a strict criterion of meaning: the so-called “verifiability criterion”.34 This criterion essentially states that a sentence that pretends to express a synthetic proposition has cognitive meaning if, and only if, it is directly verifiable – i.e. it is possible to conceive of a finite set of “protocol sentences” that would permit a conclusive determination of its truth or falsehood through the senses.35
30The logical positivists base their main objection to metaphysics precisely on this philosophy of language. In contrast to other philosophers who have opposed metaphysics, they do not deem it impossible on the basis that it concerns entities that either do not exist or cannot be known. Their argument is different and, at the same time, innovative, in that they argue that metaphysics is impossible because its sentences are simply meaningless. In this regard, the following quote from Rudolf Carnap is illustrative:
The development of modern logic has made it possible to give a new and sharper answer to the question of the validity and justification of metaphysics. ... In the domain of metaphysics ... logical analysis yields the negative result that the alleged statements in this domain are entirely meaningless. Therewith a radical elimination of metaphysics is attained, which was not yet possible from the earlier anti-metaphysical standpoints (Carnap 1959 [1932]: 61; author´s italics).
- 36 Carnap, 1959 [1932]: 79. In other words, as Ginnobili aptly observes, the issue with metaphysics, a (...)
- 37 Carnap 1959 [1932]: 77. The influence of Ludwig Wittgenstein here is undeniable. In paragraph 4.003 (...)
31In brief, they argue that metaphysical sentences are meaningless because they purport to convey cognitive meaning; they attempt to express propositions, but fail to do so, as they contain neither analytical propositions nor directly verifiable ones. Carnap points out that, as a matter of fact, these statements merely express “pseudo-propositions” – i.e. something that simulates having cognitive meaning but, at best, only conveys “an emotional reaction”.36As a result, the members of the Vienna Circle ended up suggesting that philosophy should no longer concern itself with what it has traditionally focused on: the examination of metaphysical “pseudo-problems” generated by a misuse of language. Instead, they argue that philosophers should focus their efforts on the only relevant task they can perform: providing a logical analysis of scientific language – specifically, clarifying scientific concepts to purge them of any metaphysical traces.37
- 38 Kelsen 1967 [1960]: 76; italics added.
32Let's turn to Kelsen's view on the sentences of legal science. As is likely known, Kelsen argues that the sentences of legal science are normative. This means, in his own words, that they state that: “Under certain conditions determined ... a coercive act ... ought to take place”.38 However, this assertion that the sentences of legal science are normative can be interpreted in at least two ways, and as I aim to show, neither of these interpretations is well-matched with the conception that the logical positivists have about the meaning of scientific sentences.
- 39 In this sense, Nino says: “... if that primitive judgement of validity is itself, according to Kels (...)
33One way to interpret this statement is that Kelsen is suggesting that the sentences of legal science do not actually aim to have a cognitive meaning, but rather a prescriptive one; in other words, that they do not pretend to express propositions, but prescriptions. This is how Carlos Nino interpreted it.39 Understood in this way, the irreconcilability between the pure theory of law and logical positivism is evident. Since the sentences of legal science do not aim to provide knowledge, but rather to prescribe, the members of the Vienna Circle – although they would not consider these sentences metaphysical, as they do not simulate to be something they are not – would still insist that they cannot be part of legal science.
- 40 Walter 1999: 50.
- 41 To mention just one example, in one of the passages of his Pure Theory of Law, Kelsen states the fo (...)
- 42 Kelsen 1945: 120.
- 43 Kelsen 1967 [1960]: 73.
34The second way to understand the idea that the sentences of legal science are normative is to interpret Kelsen as suggesting that these sentences aim to convey cognitive meaning; they do purport to express propositions, but “normative propositions” – i.e., propositions that describe the content of valid legal norms. This interpretation was supported by Robert Walter,40 and I believe it accurately reflects what Kelsen intended to say. Indeed, many quotes from Kelsen support this interpretation.41 Now, understood in this second way, the discordancy between the pure theory of law and logical positivism is less obvious than the previous one, but still evident. This is because if the sentences of legal science pretend to express “normative propositions”, then, according to Kelsen, what they describe are not physical entities or directly verifiable properties, but rather normative entities42 whose “validity” or “binding force” are not directly verifiable but, as Kelsen himself acknowledges, are “indirectly verifiable”.43
35In light of this, I believe that any member of the Vienna Circle would consider these sentences a paradigmatic example of “metaphysical sentences” – i.e., sentences that purport to convey cognitive meaning but fail to do so, as they express neither analytic propositions nor directly verifiable ones. In fact, this is something Carnap explicitly suggests when he refers, in general terms, to “normative disciplines”:
The same judgment [that invalidates any metaphysical speculation] must be passed on … any ... normative discipline. For the objective validity of a ... norm is ... not empirically verifiable nor deducible from empirical statements, hence it cannot be asserted (in a meaningful statement) at all (Carnap 1959 [1932]: 77).
36As can be seen, it is not at all misguided to interpret that for the logical positivists, the sentences of legal science as understood in this second way, actually express “pseudo-propositions”, namely, contents that simulate conveying legal knowledge but, at best, only reflect an emotional reaction in favour of obedience to positive law.
37The last disagreement between the pure theory of law and logical positivism concerns the nature of social sciences.
38Logical positivism is known for defending the “principle of the unity of science”. This principle asserts that the various branches of empirical science form a single and unified body of knowledge, separated only for practical reasons related to the division of labour.44 In other words, what the “principle of the unity of science” reflects is a rejection of the idea – widely held in late 19th-century German philosophy – that there is an essential distinction between natural sciences and the so-called “sciences of the spirit” (Geisteswissenschaften).
39The members of the Vienna Circle who most emphatically defended the “principle of the unity of science” were Rudolf Carnap and Otto Neurath. Nonetheless, although they agreed in broad terms, their views on how the various scientific disciplines should be unified were not exactly the same.45 Therefore, to simplify my argument, I will focus solely on Neurath's position, as he was the one who devoted more attention to the analysis of both social sciences in general and legal science in particular.
- 46 As Moulines puts it, for the logical positivists, the "physicalist language" was akin to “an Espera (...)
- 47 Neurath 1959 [1931]: 293; author´s italics.
40Neurath provides two main arguments in defence of the “principle of the unity of science”. The first argument is related to the general view that logical positivism holds regarding the language of empirical science. According to Neurath, one aspect that unifies natural and social sciences is that both can be translated into the same language: “physicalist language”.46 This means that the concepts of every empirical discipline, whether natural or social, can equally be reduced to more basic concepts that denote physical entities and directly verifiable properties. He expresses it in this succinct way: “The physicalist language, unified language, is the Alpha and Omega of all science”.47
- 48 Neurath 1959 [1931]: 296.
41Specifically, Neurath argues that the language of social sciences can be translated into “physicalist language” by adopting the vocabulary developed by “behaviourist” psychology – i.e., by reducing all its concepts to those that directly denote “human behaviour”, understood as voluntary or involuntary bodily movements of human beings.48 In this way, Neurath argues that sociology can be conceived as a “social behaviourism”; namely, as a discipline whose concepts refer to human behaviour, not of particular individuals – as in psychology –, but of groups of individuals. This leads him to the following conclusion:
... sociology is not ... the study of man´s spiritual life (Geisteswissenschaft) standing in fundamental opposition to some other sciences, called natural sciences, no, as social behaviourism, sociology is a part of unified science (Neurath 1959 [1931]: 296; author´s italics).
- 49 Neurath 1959 [1931]: 304.
42What´s more, Neurath not only states that sociology can be conceived as a “social behaviourism”, but also suggests that “ethics” and legal science can be seen as branches of sociology qua “social behaviourism”. In this sense, he explicitly states: “... the modes of behaviour on which ... 'legal' and 'ethical' judgments are passed could be integrated into sociology”.49
- 50 Neurath 1959 [1931]: 295.
43Of course, Neurath acknowledges that many philosophers tend to think the opposite: that, due to the ontology of their object, the concepts of the social sciences are irreducible to “behaviourist” vocabulary. He responds, however, that this ontological dualism is merely the product of a mental habit that has persisted as a “vestige of theology”: the belief that human beings are composed not only of a “body” but also of a “soul”.50 And for him, this mental habit is also present within the domain of the philosophy of legal science. Thus, in an obvious reference to Kelsen's theory, he argues:
What part the mental habit of theological dualism plays in the creation of such dichotomies can perhaps be gathered from the fact that as soon as one such division is discarded another easily stablishes itself. The opposition of the 'Is' and the 'Ought', which is encountered specially among philosophers of law, may be mentioned here. In part, of course, this may be traced to theological opposition of 'Ideal' and 'Reality' (Neurath 1959 [1931]: 295).
44Neurath also presents a second argument in support of the “principle of the unity of science”, which concerns the nature of scientific laws formulated by different empirical disciplines. Thus, for him, another aspect that unifies natural and social sciences is that their laws share the same logical form and function.
- 51 Neurath, following Schlick, conceived scientific laws not as propositions, but as directives – i.e. (...)
- 52 Neurath 1959 [1931]: 303.
- 53 In his words: “All laws, whether chemical, climatological or sociological, must ... be conceived of (...)
- 54 In this sense, he says: “It is, of course, possible to delimit different kinds of laws from one ano (...)
45Neurath believes that the laws of social sciences, as in natural sciences, take the logical form of directives or instructions: they indicate regularities among general facts that serve to predict particular events.51 For example, when referring to sociology, he states that “[s]ociology, like every science, tracks down correlations which can be utilized for predictions”.52 Furthermore, Neurath emphasizes that the laws of natural and social sciences are not only of the same kind but also interconnected, forming a unified system.53 Indeed, something that Neurath thinks is that one of the strongest arguments in favour of the “principle of unity of science” is that it is nearly impossible to predict any event – such as a forest fire – without, at least implicitly, combining laws from both the natural and social sciences.54
46Neurath concludes his argument by noting that everything he has asserted applies not only to sociology but also extends to the fields of “ethics” and legal science. Thus, he declares:
These disciplines are in every sense branch of sociology, but they are quite different from the 'ethics' and 'jurisprudence' which are commonly cultivated. The latter yield few or no sociological correlations (Neurath 1959 [1931]: 304).
- 55 Neurath 1959 [1931]: 305.
47In this regard, Neurath is particularly critical of the traditional practice of legal science. He argues that the work of jurists lacks scientific status not only – as previously noted – because it assumes a metaphysical dualism between “Is” and “Ought” as a vestige of theology, but more importantly because its laws do not indicate regularities suitable for making predictions.55
- 56 Kelsen 2008 [1934]: 3; translation mine, italics added.
48In contrast, Kelsen is known for defending the opposite view – i.e., that legal science is a “science of the spirit” that is essentially different from natural sciences. He makes this point clear from the very outset in the preface to the first edition of his Pure Theory of Law, where he states: “From the very beginning, my goal was to elevate the science of law to the level of a true science, a science of the spirit” (Geisteswissenschaft).56 This passage reveals that Kelsen assumes a dualistic conception, according to which natural and social sciences are essentially distinct disciplines. Indeed, he maintains that the two can be distinguished along at least two basic aspects.
- 57 Kelsen, 1960: 72.
- 58 Kelsen 1960: 169. Although Kelsen does not state it explicitly, within his classification, a third (...)
- 59 In this vein, Kelsen says: “the object of these social sciences is by no means unreal – it also has (...)
49The first aspect is ontological. One of Kelsen's central assumptions is that social sciences are normative. This means that, unlike natural sciences which, to him, study physical entities, social sciences focus on normative entities that are ontologically irreducible to the former “orders”.57 In this way, he conceives the domain of social sciences as limited to two subdisciplines: “ethics” and legal science.58 Particularly, legal science is that branch of the social sciences concerned with the study of those “orders” characterized by their coercive nature.59
50Now, if as Kelsen states, social sciences study normative entities and these, in turn, are ontologically irreducible to physical entities, it follows that the language of these disciplines cannot be translated into “physicalist language”. More specifically, their concepts could never be reduced, for instance, to “behaviourist” vocabulary. Kelsen frequently emphasizes this point and makes it explicit in relation to legal science:
The legal statements that one ought to behave in a certain way cannot be reduced to statements about present or future facts, because the former do not refer to such facts ... (Kelsen 1967 [1960]: 104).
51The second aspect that Kelsen notes differentiates social sciences from natural sciences, concerns the nature of laws they respectively formulate. Thus, one underlying idea in his Pure Theory of Law is that the laws of social sciences differ from those of natural sciences in both their logical form and function.
- 60 Kelsen 1967 [1960]: 77.
- 61 Kelsen 2008 [1960]: 152; translation mine, author´s italics.
52Thus, regarding their logical form, Kelsen argues that while the laws of natural sciences are conditional propositions that describe causal relationships – whether universal or probabilistic – the laws of social sciences are conditional propositions that describe normative relationships. In his own words, this means that the laws of social sciences, including legal science do not say, “... as the law of nature does: when A is, 'is' B; but when A is, B 'ought' to be, even though B perhaps actually is not”.60 Moreover, Kelsen holds that this different logical form reflects a more fundamental methodological difference. Thus, he states that: “In the description of a normative order ... an ordering principle, distinct from causality, is applied, which can be referred to as imputation”.61 Behind this idea is, once again, Kant. Kelsen's assumption is that the laws of natural sciences and those of social sciences employ different “categories” or “pure concepts of understanding”. Thus, on the one hand, the laws of natural sciences connect general facts according to one of Kant’s “categories”: the “principle of causality”. On the other hand, the laws of social sciences – including legal science – connect general facts through a different “category”: the “principle of imputation”. This principle describes a type of connection that does not arise from natural processes, but rather from human acts of normative creation.
- 62 In this sense, he declares: “At any rate, the science of law does not have the task of predicting c (...)
53Finally, Kelsen also argues that the laws of social sciences are not only distinguished from those of natural sciences by their logical form but also by their function. One point that Kelsen emphasizes, particularly in discussion with legal realist, is that legal science is not a predictive discipline.62 This means, quite simply, that its laws are not formulated with the aim of predicting what subjects or judges will do, but rather to describe what they ought to do in accordance with a particular legal system. On this basis, one could argue that the laws of legal science, as Kelsen conceives them, are not something worth interconnecting with other scientific laws – at least not if the goal is to accurately predict specific events, such as certain courses of action.
- 63 Walter 2001: 17; translation mine, author's italics.
54Given the three disagreements discussed above, it is worth asking why some specialized authors – even figures like Robert Walter – insist that “... the Pure Theory of Law is philosophically more connected to the Vienna Circle than separated from it”.63 As I will show below, this can be explained by certain terminological coincidences or peripheral similarities between Kelsen's thought and that of the Vienna Circle, which may – incorrectly, in my view – lead to this conclusion.
- 64 This orientation is explicitly embraced by Kelsen in several passages of his work. For example, in (...)
55The main motive for considering the pure theory of law as closely aligned with logical positivism likely has to do with its “anti-metaphysical” inclination, particularly evident in Kelsen's effort to purify legal science from natural law.64 This is indeed one of the reasons that Walter explicitly mentions to support his position. In this regard, for example, he says:
The parallelism between the philosophical efforts of the Vienna Circle and those of the Pure Theory of Law is clearly manifested ... in their anti-metaphysical positions (Walter 2001: 4; translation mine).
56This parallelism identified by Walter is further reinforced – once again – by another significant biographical detail: Kelsen himself endorses this idea. In a letter to Henk Mulder, one of the first biographers of the Vienna Circle, dated May 5, 1963, he writes:
... What connected me to the philosophy of this circle —without being Influenced by it— was its antimetaphysical thrust (Jabloner 1998: 378).
57However, contrary to what Walter and ultimately Kelsen himself thinks, this similarity is irrelevant for justifying the idea that the pure theory of law and logical positivism are closely related philosophical approaches. The reason is simple: it is merely a terminological coincidence. At the conceptual level – which is what truly matters – the similarity simply vanishes. Let me explain why.
58When Kelsen accuses natural law theory of being “metaphysical”, he is asserting an epistemological thesis about the nature of what can be known, which bears a family resemblance to Kant’s view on the matter. According to Kant, metaphysics – at least the “dogmatic” kind – is impossible because knowledge cannot be based on mere speculation, i.e., without the basic input that only sensory perception provides. Kant summarized this objection with the following statement: “... thoughts without content are empty ...”.65 In a remarkably similar way, Kelsen argues that what makes natural law theory “metaphysical” is that its starting point consists of prescriptions dictated by a supposed supernatural authority – i.e., prescriptions that transcend sensory perception and, according to Kelsen, cannot be known. He makes this clear when he says:
To say that God in nature as a manifestation of his will commands men to behave in a certain way, is a metaphysical assumption, which cannot be accepted by science in general and by legal science in particular, because scientific cognition cannot have as its object a fact which is assumed to exist beyond all possible experience (Kelsen 1967 [1960]: 221).
59On the other hand, as we have already seen, when the logical positivists criticize traditional philosophy for being “metaphysical”, they are not asserting an epistemological thesis but a semantic one. In other words, they do not aim to uphold a thesis about the nature of what can be known, but rather about the nature of what can be said. This semantic thesis essentially argues that metaphysics is impossible, not because it studies entities that cannot be known, but because its sentences are simply meaningless. And, as is probably remembered, the reason why metaphysical sentences lack meaning is that they aim to convey cognitive meaning but, in reality do not do so, since they express neither analytic propositions nor directly verifiable ones.
- 66 Neurath 1981: 898; translation mine.
60As can be seen, the concept of “metaphysics” used by the logical positivists is not necessarily opposed to that of Kant or Kelsen. In fact, the scope of the latter is included within the former. Nevertheless, it is a broader notion – or, as Carnap explicitly says, a “radical” one – that places both Kant’s epistemology and Kelsen’s philosophy of legal science within the domain of metaphysics. Indeed, according to this sharper notion, both Kant’s “synthetic a priori judgments” and Kelsen’s normative statements do belong to metaphysics. This helps clarify, in my view, why Neurath, in one of his references to Kelsen's theory, believes that although it has discarded certain theological elements historically associated with legal and state theory, it is still “... not entirely free from metaphysics”.66
- 67 Other works where Kelsen puts forward similar ideas can be found in Kelsen 1939a and Kelsen 1939b.
61The other reason why Kelsen's philosophy of legal science is often associated with logical positivism relates to a lesser-known aspect of his work: his view on the history of the concept of “causality”. Between 1936 and 1940, Kelsen conducted an ethnographic study on the origins and evolution of the principle of causality in human thought, whose most detailed version can be found in his essay Society and Nature (1943).67 This research piqued the interest – as we will see, not coincidentally – of several members of the Vienna Circle; particularly Neurath.
- 68 Kelsen 1943: vii.
- 69 The content of this rule can be expressed as follows: “Whoever acts well must be rewarded, and whoe (...)
62There, Kelsen argues that the principle of causality is not – as Kant believed – an “innate idea” but rather a contingent way of thinking that was absent for a significant period in human history.68 In this regard, he asserts that primitive societies did not interpret nature through the principle of causality but through the principle of imputation. This means that they explained natural events, such as a good or bad harvest, as rewards or punishments imposed by a transcendent and all-powerful authority in response to obedience to, or violation of, the rule of retribution.69
63It is only with the Presocratic philosophers, particularly the atomists, that the first attempt was made to provide a naturalistic explanation of the world based on the principle of causality. However, Kelsen points out that, at that time, causality was understood as a necessary relationship – i.e., one without exceptions. This suggests that for him, the principle of causality originated as a derivative of the rule of retribution, namely, the belief that certain transcendent and all-powerful authorities govern nature by dispensing rewards and punishments.70
64After a long period of decline during the Middle Ages, Kelsen explains that the atomists' conception of causality was revived with the rise of modern science. From that point on, the principle of causality increasingly distanced itself from the rule of retribution. Thus, according to Kelsen, this process of emancipation began with David Hume, who dismantled the idea that causality expresses a necessary relationship. It was then further reinforced by Ernst Mach, Philipp Frank, and Hans Reichenbach in the late 19th and early 20th centuries, as they reformulated the concept of causality in terms of statistical probability. Finally, this process culminated in Werner Heisenberg’s discovery of the uncertainty principle in quantum mechanics.71
65After presenting this historical overview, Kelsen concludes his essay with a reflection that many have found puzzling. He states:
The dualism of nature and society is by no means the last step in the evolution of science. ... After the complete emancipation of causality from retribution in the modern notion of law, society is —from the point of view of science— a part of nature (Kelsen 1943: 266).
- 72 Guevara Arroyo 2024: 12.
- 73 Jabloner 1998: 381 & 2001: 27.
66What seems to be implied in this passage is that the use of the principle of imputation by social sciences in general, and by legal science in particular, represents a vestige of the primitive way of interpreting the world; one that is ultimately destined to be overcome, sooner or later, by a modern social science based on the principle of causality. If this is the case, Kelsen would be abandoning the dualistic conception defended in his pure theory of law72 and, at the same time, moving closer to the “principle of the unity of science” proposed by the logical positivists.73
- 74 According to Paulson, Kelsen would discard his Pure Theory of Law for a second time after the 1960s (...)
- 75 Paulson 2021: 58. In this vein, Paulson claims: “[This] revolution in Kelsen’s thinking is short-li (...)
67Unlike what was noted regarding his “anti-metaphysical” orientation, we are not dealing with a mere terminological coincidence but with a rather tangible similarity. Nonetheless, this similarity is still insufficient to justify the claim that there is a philosophical affinity between the pure theory of law and logical positivism. This is primarily because it is based on ideas that occupy a peripheral place within Kelsen's thought. Indeed, as Paulson highlights, these ideas were part of a “four-year interlude” during which Kelsen “discarded” – for the first time – his pure theory of law;74 a phase from which he quickly returned as the 1940s began.75 Once that interlude was over, Kelsen restarted his defence of a dualistic conception of legal science. As an illustration of this, in the second edition of his pure theory of law, Kelsen declares:
The dualism of nature as a causal, and society as a normative, order is unknown to [...the primitive man]. That such a dualism exists in the thinking of civilized man is the result of an intellectual development during which human and ... things are distinguished, and the causal explanation of the relationships between things is separated from the normative interpretation of the relationships between men (Kelsen 1967 [1960]: 84).
- 76 Similar statements can also be found in both his General Theory of Law and State (1945) and his Thé (...)
68This quote seems to imply an opposite conclusion to the one Kelsen himself expressed in Society and Nature. What Kelsen appears to be suggesting now is that dualism is not a residue of primitive thought, but rather the result of its overcoming – i.e., a sign of a civilized mind.76
69In this final section, I aim to briefly present an additional theoretical benefit derived from the inter-theoretical comparison between the pure theory of law and logical positivism discussed above.
70In one of his articles, Stanley Paulson explains the importance of studying Kantian influence in Kelsen’s work as follows: according to him, a thorough examination of these Kantian components is the key to distinguishing Kelsen’s normative legal positivism from the “empiricist” or “naturalist” trends in legal positivism that were advocated in the 19th century.77 Similarly, I believe that comparing Kelsen’s philosophy of legal science with the Vienna Circle’s general philosophy of science is key to deeply understand the nature of the criticisms that the pure theory of law received from other legal positivists during the 20th century.
- 78 In On Law and Justice, Ross sought to establish a philosophy of legal science grounded in certain c (...)
- 79 Ross 2011 [1959]: 96.
- 80 Ross 2008 [1961]: 215; translation mine.
- 81 This means, says Ross: “... that we should not interpret the propositions [of legal science] as pro (...)
- 82 Ross 2011 [1959]: 68.
- 83 Ross 2011 [1959]: 69.
71Perhaps the most obvious example in this regard is Alf Ross's criticism of Kelsen's concept of “validity”.78 According to Ross, Kelsen´s understanding of “validity” as “binding force” is a “metaphysical construct”,79 whose sole function is to serve as an “instrument of an ideology that supports the authority of the State”.80 Therefore, he proposes excluding this concept from legal science and replacing it with one that meets the “criterion of verifiability”,81 namely, the concept of “efficacy” (Gældende).82 In this sense, Ross suggests translating statements in legal science into propositions that express scientific laws explaining and predicting the directives in force at a specific time and place —i.e., directives that judges psychologically perceive as binding and are, for this reason, highly likely to be incorporated into their rulings.83
- 84 In the context of a broader work, Guido Pincione has reached the same conclusion. In this regard, h (...)
72As is evident, Ross's criticism goes far beyond the scope of legal philosophy. At its core, it reflects a deeper disagreement at the level of the philosophy of science regarding whether legal science should employ concepts that fail to meet the “criterion of verifiability”.84 Ross himself acknowledges this when he states:
The final battle [between metaphysical idealism and scientific realism] cannot be fought within the domain of legal philosophy but must take place in the field of general philosophy. The controversy between idealism and realism in the philosophy of law necessarily dissolves into fundamental problems of epistemology (Ross 2011 [1959]: 97; translation mine; italics added).
- 85 In fact, in an article I find insightful, Bulygin proposes retaining several substantial theses fro (...)
73And I suspect that something similar occurs with other legal positivist authors who have criticized Kelsen's pure theory of law. For instance, Eugenio Bulygin’s objections against Kelsen’s thesis, which claim that all norms establish coercive sanctions and are consistent with one another, also reflect a disagreement that goes well beyond legal philosophy and extends to the level of the philosophy of science. This disagreement is directly linked to the “transcendental idealist” assumption that legal science must construct its object through the use of the “basic norm” category.85
74In this article, I aimed to provide an inter-theoretical comparison between the pure theory of law and logical positivism. The specific question I sought to address was whether the pure theory of law is philosophically close to logical positivism or whether it should be considered a rather distant philosophical approach.
75The limited existing literature reveals significant disagreement among prominent experts on this matter. Therefore, the primary goal of this article has been to settle this debate. To achieve this, I structured the exposition into three parts. In the first, I explained why the pure theory of law and logical positivism should be definitively regarded as philosophically distant approaches. My central argument was that their theoretical gap arises from three fundamental disagreements within the philosophy of science: (i) the foundation of scientific knowledge – logical positivism embraces empiricism, while the pure theory of law adopts a “transcendental idealist” approach; (ii) the meaning of scientific sentences – logical positivism holds that scientific sentences express either analytic or synthetic propositions, whereas Kelsen contends that sentences of legal science are normative; and (iii) the nature of social sciences – logical positivism endorses the “principle of the unity of science”, while the pure theory of law advocates a dualistic perspective.
76In the second part, I argued that the two aspects of Kelsen's thought commonly cited to link his philosophy of legal science with logical positivism are insufficient to support such a claim. First, the “anti-metaphysical” character of the pure theory of law reflects only a terminological similarity with logical positivism, rather than a conceptual one. Second, although Kelsen's perspective on the history of the concept of “causality” shows a real affinity with logical positivism, it occupies a peripheral place within Kelsen's thought.
77In the third part, I emphasized an additional theoretical benefit that arises from this inter-theoretical comparison. In my view, this comparison provides a deeper understanding of the nature of the criticisms that the pure theory of law received from other legal positivists throughout the 20th century, such as the paradigmatic critiques put forward by Alf Ross and Eugenio Bulygin.
–Acknowledgments.– This work was carried out as part of the research project SADAF 2023/003, funded by the Sociedad Argentina de Análisis Filosófico and jointly directed by Gabriela Scataglini and myself. I am especially grateful to those who read earlier drafts of this manuscript and offered valuable critical feedback, in particular: Marcelo Alegre, Nancy Cardinaux, Sebastián Chavarría, Andreas Funke, Paula Gaido, Juan González Bertomeu, Alejandro Guevara Arroyo, Matías Manelli, José Juan Moreso, Claudina Orunesu, Florencia Rimoldi, Jorge Rodríguez, Gabriela Scataglini, Jan Sieckmann, Oscar Sarlo, Horacio Spector, Marina Velasco and Hugo Zuleta. I would also like to express my gratitude to the anonymous reviewers for their thoughtful suggestions.