Concepts are the building blocks of legal doctrine. All legal rules and standards, in fact, are formed by combining concepts in different ways. But despite their centrality, legal concepts are not well understood. There is no agreement as to what makes a legal concept useful or ineffective—worth keeping or in need of revision. Social scientists, however, have developed a set of criteria for successful concepts. Of these, the most important is measurability: the ability, at least in principle, to assess a concept with data. In this Essay, we apply the social scientific criteria to a number of concepts and conceptual relationships in American constitutional law. We show that this field includes both poor and effective concepts and conceptual links. We also explain how the examples of poor concepts could be improved.


A common contrast, first articulated in Professor H.L.A. Hart’s classic The Concept of Law, is between an “external” or social scientific view of law and an “internal” view, which emphasizes law’s normativity.1 The so-called external view of law, in which law is conceived of as being essentially predictions about what courts will do, dates back at least to Justice Oliver Wendell Holmes and arguably to John Austin or Montesquieu.2 The internal view is that adopted by participants within the legal system, be they judges, litigants, or lawyers, and includes all the normative and doctrinal considerations that inform legal decisions.

Legal scholarship has moved in an overtly empirical direction in recent years, and, arguably, there has been some improvement in our external understanding of legal phenomena.3 The technology for making Holmesian predictions has improved dramatically, largely because of developments in the social sciences. Consequently, the external view has made great strides in many areas of legal scholarship, and some critics argue that it has eroded attention to the internal view.4 Yet the two are also closely linked.

In this Essay, we argue that social science can inform an internal view of law by improving the formation and linkage of legal concepts. The social science literature on conceptualization and measurement is vast, particularly in political science, psychology, and sociology.5 Yet its insights have been largely ignored by lawyers, notwithstanding some similarities to the architecture of legal thought. Law, after all, involves language organized into concepts, structured in a way that lawyers can deploy them. Concepts are the very bread and butter of daily life, and, of course, of law as well. Negligence, a taking, promissory estoppel, strict scrutiny—each of these is a formulation that involves a particular conceptual structure and helps to shape the way lawyers approach legal problems. Our argument is that examining legal doctrines with the same rigorous scrutiny that social scientists apply to their own efforts can yield insights into what is a useful legal concept or relationship. And we further suggest this will advance efforts at refinement within the law. We deploy several examples from constitutional law to illustrate our claim, but the implications are more general.

Before proceeding, let us be clear that, notwithstanding the title of our Essay, this is not a work of jurisprudence. We are not interested, as Hart was, in the concept of law itself.6 We set aside the question of what law is, as well as the relative roles of natural law or positivist approaches to that question.7 Rather, we are interested in the way law uses concepts. Although we have made significant advances in our predictive understanding of judicial behavior, there has been little effort to apply the same insight to the articulation of the law itself. Our effort provides an external vantage point from which to assess the law’s conceptual apparatus, which in turn might inform the law’s normative development.

Note also that we are not grappling with nonlegal concepts that are often deployed within the law. Obviously, law seeks to advance values, like justice, fairness, or democracy, that are not themselves inherently legal in character. These values provide benchmarks against which legal systems can be measured, and might themselves be subjected to social science scrutiny.8 But these are not themselves legal concepts in our view, even if they are used to motivate legal intervention.

The Essay is organized as follows. First, we provide a sketch of the social science literatures on conceptualization and measurement. We emphasize the desiderata of a good social science concept, one of which is that the concept should in principle be subject to empirical evaluation. Next, we consider the relationships between concepts, which we argue are a central feature of the law. At the most basic level, the application of any legal test is assumed to advance another concept, like justice or deterrence. Internally, within the law, concepts are also building blocks of legal rules, and can be bundled together in various ways.9 Our argument is that these links are most useful when empirically verifiable, at least in principle. The next Part provides a series of examples, drawn primarily from constitutional law, though our claim is more general. These examples cover both concepts and conceptual relationships, and both poor and effective cases. We conclude with a brief discussion of implications and extensions.

  • 1. H.L.A. Hart, The Concept of Law 86–88 (Clarendon 1961) (distinguishing the internal and external points of view). See also generally Scott J. Shapiro, What Is the Internal Point of View?, 75 Fordham L Rev 1157 (2006) (exploring tensions in Hart’s perspective).
  • 2. See Oliver Wendell Holmes Jr, The Path of the Law, 10 Harv L Rev 457, 457 (1897) (“The object of our study, then, is prediction, the prediction of the incidence of the public force through the instrumentality of the courts.”). See also Robert S. Summers, Professor H.L.A. Hart’s Concept of Law, 1963 Duke L J 629, 631 (summarizing Austin’s arguments); Arthur H. Garrison, The Traditions and History of the Meaning of the Rule of Law, 12 Georgetown J L & Pub Pol 565, 575–76 (2014) (describing Montesquieu’s position).
  • 3. See Theodore Eisenberg, The Origins, Nature, and Promise of Empirical Legal Studies and a Response to Concerns, 2011 U Ill L Rev 1713, 1715–19; Michael Heise, An Empirical Analysis of Empirical Legal Scholarship Production, 1990–2009, 2011 U Ill L Rev 1739, 1741–46; Shari Seidman Diamond and Pam Mueller, Empirical Legal Scholarship in Law Reviews, 6 Ann Rev L & Soc Sci 581, 592 (2010).
  • 4. See, for example, Charles L. Barzun, Inside-Out: Beyond the Internal/External Distinction in Legal Scholarship, 101 Va L Rev 1203, 1245–58 (2015).
  • 5. See, for example, Giovanni Sartori, Concept Misformation in Comparative Politics, 64 Am Polit Sci Rev 1033, 1035 (1970); Gary Goertz, Social Science Concepts: A User’s Guide 27–67 (Princeton 2006); John Gerring, Social Science Methodology: A Unified Framework 107–40 (Cambridge 2d ed 2012); Gary King, Robert O. Keohane, and Sidney Verba, Designing Social Inquiry: Scientific Inference in Qualitative Research 97–114 (Princeton 1994); David Collier, Jason Seawright, and Gerardo L. Munck, The Quest for Standards: King, Keohane, and Verba’s Designing Social Inquiry, in Henry E. Brady and David Collier, eds, Rethinking Social Inquiry: Diverse Tools, Shared Standards 21, 21–26 (Rowman & Littlefield 2004); Henry E. Brady, Doing Good and Doing Better: How Far Does the Quantitative Template Get Us?, in Brady and Collier, eds, Rethinking Social Inquiry 53, 62–66 (cited in note 5); Gary Goertz, Concepts, Theories, and Numbers: A Checklist for Constructing, Evaluating, and Using Concepts or Quantitative Measures, in Janet M. Box-Steffensmeier, Henry E. Brady, and David Collier, eds, The Oxford Handbook of Political Methodology 97, 98–114 (Oxford 2008).
  • 6. See Hart, The Concept of Law at 1 (cited in note 1).
  • 7. See H.L.A. Hart, Positivism and the Separation of Law and Morals, 71 Harv L Rev 593, 593–94 (1958) (presenting the positivist viewpoint); Lon L. Fuller, Positivism and Fidelity to Law—a Reply to Professor Hart, 71 Harv L Rev 630, 630–32, 671–72 (1958) (responding from a natural law perspective).
  • 8. Indeed, a large literature grapples with the rule of law as a concept. See, for example, Jørgen Møller and Svend-Erik Skaaning, The Rule of Law: Definitions, Measures, Patterns and Causes 1–3, 13–14 (Palgrave Macmillan 2014).
  • 9. See Peter de Bolla, The Architecture of Concepts: The Historical Formation of Human Rights 40–47 (Fordham 2013).