Each of the three disciplines has a distinct perspective with specific substantive research interests and its own methodological approach. I have so far been optimistic about the synergies between these three perspectives, but one could be more sceptical: If the questions asked and the answers given are articulated in a different language, is it worthwhile to try to combine them?
My argument so far assumed that the hints at empirical and doctrinal knowledge from within legal philosophy are a first step toward collaboration between the disciplines to find support for these kinds of arguments, but it is possible to argue in the other direction. Maybe it is advisable to steer clear of empirical and doctrinal arguments altogether and limit the legal philosophical argument to conceptual and/or value-based reasoning only. Various legal philosophers characterize and justify their own approaches in contrast to sociology of law, arguing against the need to engage with socio-legal work.Footnote 49 Raz, for example, sees legal philosophy as engaging with universal and necessary characteristics of law, while sociology of law describes particulars of various legal systems. As Raz states, sociology of law ‘provides a wealth of information’ on contingent features of existing legal systems, while legal philosophy needs to focus on ‘those few features that all legal systems necessarily possess’.Footnote 50 However, this division of labour is questionable: How do we know what the necessary features are without knowledge of the contingent features? As I have argued in Section II, features that are presented as necessary for the rule of law, such as independent courts, may turn out to be contingent upon further examination. As Giudice argues, there is good reason for legal philosophers to expand their research beyond the necessary and universal characteristics of law, which he sees as a need to move from conceptual analysis to ‘constructive conceptual explanation’ in order to address the observed pluralism of existing conceptions of law.Footnote 51
As must be clear from the earlier discussion, I agree with Giudice that we need to move beyond legal philosophy as a self-contained project. An important reason for this point of view is that even clearly conceptual and normative arguments are embedded in traditions of thought that have been influenced by historical events and practices in society and law. Ignoring the interactions between concepts and values, on the one hand, and social and legal practices, on the other, impoverishes normative and conceptual work. An important question, therefore, is how the recognition of the pluralism of traditions and conceptions of rule of law, as of law more generally, affects the project of legal philosophy: How should the challenge of pluralism be taken up? One way of doing this is by limiting the amount or scope of universal characteristics. Raz, for instance, clearly sees municipal legal systems as the central category to be analysed.Footnote 52 There is no need for a conceptual analysis that includes non-state or international law. A second and third possibility are based on an explicit acknowledgement of the diversity of forms of law. Giudice’s solution is to look for general contingent features rather than universal and necessary features, thus admitting that a conceptual construction may leave some instances of law unexplained.Footnote 53 By contrast, the third possibility is to pluralize the concept of law itself, claiming that there is a set of plural legal forms. Lon Fuller’s work on enacted versus interactional law is a good example.Footnote 54 This can be construed as a claim of necessary pluralism: Both forms of law need to be part of the concept in order to grasp the notion of law. The latter two approaches are both productive ways of engaging with pluralism. Since various responses to plurality are possible, I do not think it provides a knockdown argument against the possibility of universal characteristics, although these may be so few that their explanatory power is very limited.
Continuing then with the exploration of the combination of perspectives, an idea from social science methodology may serve as a starting point. In social sciences, an often-used methodology is that of triangulation: using different methods to answer the same question in order to corroborate or complement results.Footnote 55 The assumption is that finding the same results with different methodological tools strengthens the support for those results, and makes the conclusions better warranted. Thus, if a researcher interested in the role of cultural differences in the courtroom finds that his interviews with judges show that they regard defendants from cultural minorities differently, and that his courtroom observations point out differences in the interactions between judges and defendants from minority groups compared to defendants from the dominant culture, and that analysis of verdicts shows differences in justification, such triangulation may be said to strengthen the conclusion that judges are sensitive to cultural differences between defendants.Footnote 56 In this example, the methods discussed are all forms of qualitative research, and they can all be used to answer the same question. Such corroboration is more problematic when the combination is between methods that are very different in orientation. Triangulating quantitative and qualitative research methods is less likely to lead to comparable results, not least because these methods are suited to answer different types of questions. Interviews, for example, suit research into perceptions and reasons people have, while experiments are a proper technique to find correlations and possible causes. This does not necessarily entail that triangulation with such diverse methodological tools is not possible; rather it shows that methodological triangulation does not always serve the purpose of corroborating results, but may also serve to complement different insights. If we acknowledge that methods have limited suitability, i.e., they can only be used to answer particular types of questions, then it makes sense to combine methods to overcome these limitations. Thus, in the example of cultural differences in the (criminal) courtroom, we may want to include differences in sentencing outcomes, an aspect that is best researched by analysing a large data set.
Once the complementary form of triangulation is accepted as a valid strategy, interdisciplinary triangulation can be seen as a natural next step.Footnote 57 Here too, the methods complement each other and may serve to uncover aspects that the other discipline cannot see or can only partly understand. Making the argument for complementarity between legal philosophy, empirical socio-legal science and legal doctrinal scholarship requires a sense of the distinctive contributions of each and possible connections between them.
Legal philosophy is distinctive in its use of conceptual arguments about core ideas in law, many of which are normative, such as rules or rights, or have a normative aspect, such as authority or courts. The focus on normative ideas also creates a need for normative arguments to support the substance of these ideas. Characteristic of the methods of legal philosophy is the construction of theoretical arguments based on various conceptual elements leading to a coherent account of basic ideas about law. In practice, the methods are primarily discursive: examining arguments and counter-arguments, building on existing theoretical work and aiming to improve on that work by presenting an alternative or modified account. Abstract theoretical arguments are confronted with concrete elements in various forms: common sense judgments or everyday language use, hypothetical or real examples.Footnote 58 The aims of legal philosophy may differ:Footnote 59 They may be descriptive, aiming to make sense of the meaning and use of legal (normative) concepts, or normative, aiming to justify the use of certain normative principles or values or to argue for the superiority of a particular conception. For example, Paul Gowder’s book on the rule of law is in large part a normative argument why the book’s central concept of the rule of law should be interpreted as requiring equality, but it also makes use of conceptual arguments about the various elements of the rule of law ordinarily included in the rule of law.Footnote 60 His conceptual and normative arguments are not neatly separated but combined in a larger philosophical argumentation. This is different in analytical philosophy, which focuses on conceptual analysis, but I do not take analytical legal philosophy to stand for legal philosophy in general.Footnote 61 Moreover, as we have seen in relation to Raz, when it comes to discussions of the rule of law, philosophers who do analytical work often engage in normative argument as well. Thus, in philosophical accounts of the rule of law, the combination of conceptual and normative argument, as also shown by Gowder, is quite common. Starting from the assumption that the rule of law is a political ideal, arguing the value of the rule of law is an important task for legal philosophy. Although I have not stressed this in the previous discussions, Waldron uses arguments about the moral value of human agency and respect for dignity to underpin his account, while also providing conceptual arguments for his procedural rule of law.Footnote 62
By contrast, empirical social science focuses on providing factual evidence to understand what people do and believe. The centrality of data is characteristic: gathering and analysing facts in various ways, with an emphasis on finding information. In empirical research, the rule of law as a concept can be measured (do actual practices conform to it?) or compared to what people believe and do (as the example of Hertogh’s research showed). Empirical research is therefore not so much interested in justifying these values as it is in understanding or explaining why they are upheld or not. The values of the rule of law are taken as a measurement criterion or transformed into something that is part of people’s actual beliefs and practices. In this article, I focus primarily on the latter, the research on cultural understandings of the rule of law, while there is also a good deal of research on the rule of law from a more quantitative angle. This would lead to including other disciplines such as economics and political science as the empirical perspective.Footnote 63 The reason for my focus on this form of socio-legal studies lies in the arguments that are needed to complement the views of Waldron and Raz: Their argumentation leads in this direction.
The distinctiveness of legal scholarship is the most difficult to grasp, but here the focus is on the normative content of the law as an institutionalized coherent practice. Legal doctrine focuses on the meaning of legal texts in a particular institutional setting, of a legal system or particular legal regime, often in comparison to other systems or regimes, and studies these texts in that context. Because of its contextual and institutional orientation, it can provide detailed descriptions that clarify relations between norms, procedures, roles and arguments. Because of its focus on coherence, it pays specific attention to the relation between the particulars of the text or case and the larger whole of the system.Footnote 64 Legal doctrinal scholarship does not question the value of the rule of law but is interested in how it works in specific legal contexts.Footnote 65
Considering the similarities and differences between the three disciplines, legal philosophy and doctrinal legal scholarship seem linked more closely than either of them is to empirical socio-legal science. The difference between the first two can be characterized as focus on the general versus the particular: where legal philosophy tends towards general arguments, doctrinal scholarship focuses on the way law is applied concretely in particular contexts, and on comparison of these particular instances. There are also significant similarities, which can be summarized as a hermeneutic methodology: linking descriptive and normative aims and arguments and using interpretive and argumentative reasoning. Empirical socio-legal science, by contrast, focuses on description and explanation, staying away from normative claims, and uses a data-based empirical method.
One way to view complementarity of these three disciplinary perspectives is to advocate a division of labour in a strict order: First, legal philosophy provides a careful argument for a particular conception of the rule of law; second, legal doctrinal scholarship shows how the rule of law conception is given a particular shape and applied in legal institutions and third, empirical science uses this conception to find out whether actual rule-of-law practices deserve to be labelled ‘rule of law’, and whether what goes on in the rule-of-law institutions has meaning in people’s everyday lives. In various combinations, such work is done.Footnote 66 However, more interesting combinations go beyond complementarity and critically reflect upon the other disciplines. Ideally, the criticized discipline takes on board the criticism and tries to reorient itself to incorporate it. Thus, the most demanding form of triangulation of perspectives is to allow for corrections of one’s own perspective based on the criticism voiced by the others. This requires a sensitivity to each other’s projects, acknowledging the value of the other perspective. It entails thinking about the way in which one’s criticism may be received by the discipline under scrutiny, being careful to avoid complete dismissal and posing questions in such a way that it opens up new directions for the other discipline. This is not to say that fundamental critique is always unwarranted; there is an argument to be made, for instance, for criticizing the philosophical idea of the rule of law as biased towards liberal individualism.Footnote 67
The idea of triangulating legal philosophy, empirical social science and legal doctrinal scholarship can be criticized for two types of reasons: conceptual and methodological. The conceptual objection is that my classification of the three disciplines is wrong: Why distinguish these three? Other theorists advance an interdisciplinary methodology for legal theorists who draw the lines in different places. An attempt to do this for rule-of-law research is Paul Gowder’s book, The Rule of Law in the Real World, in which he makes a combination of conceptual/normative legal philosophy with empirical work. He puts law and philosophy in the same camp, as the providers of ‘normative/conceptual tools’.Footnote 68 However, he also lists law as one of the disciplines providing knowledge of ‘real-world institutions’,Footnote 69 which makes it seem as if the discipline of law has a double function in Gowder’s account: both the source of normative principles and the provider of knowledge of real institutions. This points to the difficulty of distinguishing the normative and the descriptive in the legal field.Footnote 70 However, if our interest is in the justification of conceptions of the rule of law, it is important to keep track of the kind of argument advanced – conceptual, empirical, or institutional – because the support needed for such arguments differs. Another interesting argument, about the concept of law rather than the rule of law, is given by Michael Giudice, in Understanding the Nature of Law. Giudice argues for the need to combine conceptual legal philosophy with empirical social science and moral theory, leaving out legal doctrinal work. In his framework, it seems that legal doctrine does no more than provide the problems to which the combination of the other three disciplines gives answers. As will be apparent from my earlier account, I think this misses the important contribution of legal doctrinal scholarship as providing contextual arguments about the institutional side of the rule of law.Footnote 71
An objection to my idea of triangulating distinct perspectives could be that it stops short of what good scholarship should do, namely to integrate perspectives. Rather than argue that there are three different perspectives that need to speak to each other, one could argue that insights from each of these perspectives need to be synthesized into a disciplinary perspective of its own.Footnote 72 Dagan and Kreitzer make this argument in their defence of legal theory as a middle position between what they see as the dominant other approaches to law: law as craft, law and policy and sociohistorical analysis of law. Philosophy of law could well be added as a fourth corner to which their idea of legal theory relates: ‘One manifestation of the significance of law and craft for legal theory is legal theory’s tendency to be less abstract than the philosophical, economic, or other theories with which it interacts’.Footnote 73 What is crucial in their account is that legal theory is a ‘synthesis’ necessary to deal with law as a complex and multi-faceted phenomenon.Footnote 74
The triangulation idea advanced here is more modest: Rather than claim that we need a synthetic discipline of legal theory, I think it is ambitious enough to ask of the separate disciplines working on the rule of law to take seriously the implications of the other disciplines for their own work. Thus, legal philosophers need to take on board the developments in legal doctrinal scholarship and socio-legal studies that are a reason to question certain preconceived ideas, like the notion that the state legal system is the central case to account for.Footnote 75 This may be reason to investigate how a universalizing approach of the rule of law can respond to pluralism arguments. How such triangulation might work is best explained by way of an example.