1. The literature on comparative reasoning by courts has increased significantly in the last two decades and cannot be summarized here. For a reasoned reconstruction of this debate see Taavi Annus, “Comparative Constitutional Reasoning: the Law and Strategy of Selecting the Right Arguments” (2004) 14 Duke J Comp & Int’l L 301; Bobek, Michal, Comparative Reasoning in European Supreme Courts (Oxford: Oxford University Press, 2013)Google Scholarat 9-18. Empirical research on the use of comparative reasoning by European courts has been carried out by Martin Gelter & Mathias M Siems, “Citations to Foreign Courts—Illegitimate and Superfluous, or Unavoidable? Evidence from Europe” (2014) 62 Am J Com L 35. The term “foreign law” will be used in this paper in a very broad sense: it will refer to legal norms which do not belong to the legal order in which a given court operates. Moreover, by “domestic law” I will not mean state-law only, but whatever set of norms which constitutes a legal order. It has to be noted that the subject of comparative reasoning by courts includes various sorts of foreign legal materials, such as judicial decisions, legal provisions, doctrinal opinions, etc. In this paper I will focus on the comparison between legal norms broadly seen as directives of action used by courts to decide a legal case.

2. See, among others, Austen L Parrish, “Storm in a Teacup: The U.S. Supreme Court’s Use of Foreign Law” (2007) U Ill L Rev 637; David Fontana, “Refined Comparativism in Constitutional Law” (2001) 49 UCLA L Rev 539.

3. See Eric Posner & Cass Sunstein, “The Law of Other States” (2006) 59 Stan L Rev 131 at 137; Antonin Scalia, “Foreign Legal Authority in the Federal Courts” (2004) 98 American Society of International Law Proceedings 305. In the U.S. more than twenty state legislatures have so far proposed measures that either bans state courts from relying on foreign legal materials or strongly disfavours this practice: see Martha F Davies, “Shadow and Substance: The Impacts of the Anti-international Law Debate on State Court Judges” (2013) 47 New England L Rev 631.

4. See Waldron, Jeremy, “Partly Laws Common to All Mankinds.” Foreign Law in American Courts (New Haven: Yale University Press, 2012) ch 3;Google ScholarFedtke, Jörg, Judicial Recourse to Foreign Law. A New Source of Inspiration? (New York: Routledge, 2006)Google Scholarch 3; Anne-Marie Slaughter, “Judicial Globalization” (2000) 40 Va J Int’l L 1103.

5. Fredrich Schauer, “Authority and Authorities” (2008) 94 Va L Rev 1935. According to Schauer, a norm is authoritative even as it provides content-independent reasons for action, i.e., when the reason to perform the action which is required by the law does not depend on the nature or merit of this action, but on the very fact that it is so required. On the idea of authority as content-independent seeHart and Obligation”, 1958 Hart, HLA, “Legal and Moral Obligation” in Melden, AI, ed, Essays in Moral Philosophy (Seattle: University of Washington Press, 1958) at 102Google Scholar; Hart, HLA, Essays on Bentham: Studies in Jurisprudence and Political Theory (Oxford: Oxford University Press, 1982) at 254–55Google Scholar; Raz, Joseph, The Morality of Freedom (Oxford: Clarendon Press, 1986) at 35–37Google Scholar; Green, Leslie, The Authority of the State (Oxford: Clarendon Press, 1990) at 41–62.Google Scholar

6. Schauer, supra note 5 at 1960.

7. Woods, Cf John & Walton, Douglas, Fallacies: Selected Papers 1972-1982 (Berlin: De Gruyter, 1989) at 15–24Google Scholar; Grootendorst, Frans van Eemeren & Rob, Argumentation, Communication, and Fallacies. A Pragma-dialectical Perspective (Hillsdale: Lawrence Erlbaum, 1992) at 136–37Google Scholar; Eemeren, Frans van, Strategic Maneuvering in Argumentative Discourse. Extending the Pragma-dialectical Theory of Argumentation (Amsterdam-Philadelphia: Benjamins, 2010) at 202–03Google Scholar; Walton, Douglas, Reed, Chris, & Macagno, Fabrizio, Argumentation Schemes (Cambridge: Cambridge University Press, 2010) at 314.Google Scholar

8. MacCormick, Neil, Rhetoric and the Rule of Law. A Theory of Legal Reasoning (Oxford: Oxford University Press, 2009) at 143.Google Scholar

9. As one can see, this meaning is not that of Dworkin, who uses the term “coherence” to refer to a methodology of legal interpretation according to which a court has to seek a reflective equilibrium between legal principles, on the one hand, and the judgment about what is right in the particular case, on the other. Dworkin, Cf Ronald, Taking Rights Seriously (Cambridge: Harvard University Press, 1977) at 159–68.Google Scholar

10. On the existence of norms as members of a legal order, the identity criteria of legal orders, and the relationship between existence and validity of legal norms, see Raz, Joseph, The Concept of a Legal System. An Introduction to the Theory of Legal System, 2nd ed (Oxford: Clarendon Press, 1980) at 187Google Scholar; Alchourrón, Carlos E & Bulygin, Eugenio, “The Expressive Conception of Norms” in Hilpinen, H, ed, New Essays in Deontic Logic (Dordrecht: Reidel, 1981) at 95–124.Google Scholar

11. See Aarnio, Aulis, On Legal Reasoning (Turku: Turun Yliopsito, 1977) ch 1.Google Scholar

12. Notice that an argument which is logically invalid—in the sense that its conclusion does not necessarily follow from its premises—can still be a good legal argument in that the conclusion is taken to be legally justified in a certain legal order. See on this van Eemeren, Frans & Grootendorst, Rob, A Systemic Theory of Argumentation. The Pragma-dialectical Approach (Cambridge: Cambridge University Press, 2004) ch 7Google Scholar; Walton, Douglas, Informal Logic. A Pragmatic Approach, 2nd ed (Cambridge: Cambridge University Press, 2008) at 150.Google Scholar

13. One might object to the notion that by interpreting a legal text courts always integrate or modify the content of the law. According to Hart, interpretation comes into play when a legal text is vague, so that the law does not provide a clear answer to a legal issue: Hart, HLA, The Concept of Law, 2nd ed (Oxford: Clarendon Press, 1994) ch 7.Google ScholarTherefore, legal interpretation could not be based upon existing law: it would create new law which “integrates” the existing one. I find this picture not fully satisfying. Legal interpretation comes into play “when there is a possibility of argument as to the meaning of the law”, i.e., when (actual or potential) disagreement arises as to the content to be ascribed to an authoritative legal text on the basis of legal reasons, in spite of the fact that this text (or its content) is vague. See Endicott, Timothy, “Legal Interpretation” in Marmor, A, ed, The Routledge Companion to the Philosophy of Law (New York: Routledge, 2012) 112.Google ScholarIn this view, legal interpretation identifies the content that an authoritative legal text can reasonably express in a given legal context. If this is the case, interpretive reasons or arguments can be clearly distinguished from integrative ones: interpretive arguments justify the interpretation of existing legal texts, whereas integrative arguments justify either the extension of a regulation to a case that is not covered by existing legal texts or the construction of implicit legal norms.

14. On the distinction between positive and negative coherence relations see Damiano Canale & Giovanni Tuzet, “Use and Abuse of Intratextual Argumentation in Law” (2012) 3 Cogency 33. See also Fontana, supra note 2 at 539.

15. Atkins v Virginia, 536 US 304 (2002), 316. In particular, the court took into consideration the point of view of the European Union and its Members States on the matter.

16. The incompatible relation between norms holds that it is not possible to comply with N₁ when one is complying with N_x and vice versa.

17. R v Keegstra [1990] 3 SCR 697, 740. As David Beatty has pointed out, “Although U.S. authorities are frequently referred to by the [Supreme Court of Canada], it has, for the most part, treated them very cautiously and usually as not being very helpful in fashioning solutions that are appropriate for Canada.” David Beatty, “The Canadian Charter of Rights: Lessons and Laments” (1997) 60 MLR 481 at 482. Comparative reasoning has often been used in a “negative” way by the Supreme Court of South Africa in order to differentiate its interpretation of fundamental rights from the U.S. and Canadian adjudication on the matter : see, e.g., S v Makwanyane [1995] CCT 3/94 ZACC 3, paras 57 ff; Carmichele v The Minister of Safety and Security [2010] CCT 48/100 AHRLR 208, para 36; Mohamed v President of the Republic of South Africa [2001] CCT 17/01 ZACC 18, paras 46 ff.

18. The U.S. Supreme Court has sometimes adopted this kind of reasoning as well. See for instance Roper v Simmons, 543 US 551 (2005), 576–77.

19. In Henderson the House of Lords used both the positive and negative version of comparative reasoning to justify its ruling. The Court examined how the problem of the possibility of concurrent claims from breach of duty under a law of contract and a law of tort had been solved in other jurisdictions, and took into consideration both legal orders in which a concurrent remedy is admitted and legal orders in which concurrence is rejected : Henderson v Merrett Syndicates [1995] 2 AC 145, 184–85.The same approach was adopted by the House of Lords in White v Jones [1995] 2 AC 207.

20. One of the necessary features of legal orders are their “supremacy claim”: every legal order “claims authority to regulate the setting up and regulation of other institutionalized systems by its subject-community” and to reject any claim to supremacy over the same community made by another legal order. See Raz, Joseph, The Authority of Law (Oxford: Oxford University Press, 1979) at 101–02 and 118.Google ScholarTherefore, foreign legal norms are not directly relevant in a domestic legal order: a legal order may attribute relevance to these norms by making reference (renvoi) to them or by giving legal effect to them. In these cases, domestic legal orders grant permission to foreign norms to operate in the domestic jurisdiction but without those norms thereby becoming part of the legal order in question.

21. See Koen Lenaerts, “Interlocking Legal Orders in the European Union and Comparative Law” (2003) 52 Int’l & Comp LQ 876.

22. Joined Cases C-46/93 and C-48/93 Brasserie du Pêcheur SA and Factortame [1996] ECR I-1029.

23. Notice that EU courts resort to comparative reasoning also as an interpretive argument. In Díaz García (T-43/90), the CFI claimed that the provisions of EU law “which make no express reference to the law of the Member States for the purpose of determining their meaning and scope” must normally be given an “independent interpretation.” The court considered, however, that “in absence of an express reference, the application of Community law may sometimes necessitate a reference to the laws of the Member States where the Community court cannot identify in Community law or in the general principles of Community law criteria enabling it to define the meaning and scope of such a provision by way of independent interpretation.”

24. Lenaerts, supra note 21 at 873. See also Pierre Pescatore, “Le recours, dans la jurisprudence de la Cour de justice des Communautés européennes, à des normes déduites de la comparaison des droits des États membres” (1980) 32 Revue internationale de droit comparé 337.

25. In this paper I assume that there exists an EU legal order which is distinct from and in addition to the legal orders of the EU’s Member States. This assumption is highly disputed, however: see, among others, Neil MacCormick, Questioning Sovereignty: Law, State, and Nation in the European Commonwealth (Oxford: Oxford University Press, 2002) ch 7; Mattias Kumm, “The Jurisprudence of Constitutional Conflict: Constitutional Supremacy in Europe before and after the Constitutional Treaty” (2005) 11 Eur LJ 262; Julie Dixon, “How Many Legal Systems? Some Puzzles Regarding the Identity Conditions of, and the Relations between, Legal Systems in the European Union” (2008) 2 Problema. Anuario de filosofía e teoría del derecho 9.

26. Nelson Lund & John O McGinnis, “Lawrence v Texas and Judicial Hubris” (2004) 102 Mich L Rev 1555 at 1581.

27. Lawrence and Tyron v Texas, 539 US 558 (2003), 573. The Supreme Court has held that the views of “other nations that share our Anglo-American heritage, and by the leading members of the Western European community” were worth being considered in constitutional interpretation: Thompson v Oklahoma 487 US 815 (19988), 830-31.

28. Naz Foundation v Government of NCT of Delhi [2009] WP(C) 7455/2001.

29. Vikram Raghavan, “Navigating the Noteworthy and Nebulous in Naz Foundation” (2009) 11 NUJS L Rev 397. See also Madhav Khosla, “Inclusive Constitutional Comparison: Reflections on India’s Sodomy Decision” (2011) 59 Am J Comp L 909.

30. Roper, supra note 18 at 627 (Justice Scalia dissenting).

31. John G Roberts, “Confirmation Hearing on the Nomination of John G. Roberts, Jr. to be Chief Justice of the United States Before the S. Comm. on the Judiciary” (2005) 109th Cong 201.

32. On the idea of using counterfactual statements to make explicit what is implicit in an exchange of reasons in a discursive practice, see Brandom, Robert B, Between Saying and Doing. Toward an Analytic Pragmatism (Oxford: Oxford University Press, 2008) at 80 and 96–98.Google Scholar

33. This argumentative step is analogical in nature. The court is called upon to identify a common property of two or more norms which is relevant as to the case at hand. On the relevance criteria in analogical reasoning see Damiano Canale & Giovanni Tuzet, “The A Simili Argument: An Inferentialist Setting” (2009) 22 Ratio Juris 499.

34. Case 294/83 Les Verts v Parliament [1986] ECR 1339, para 23. See Miguel P Maduro, “Interpreting European Law: Judicial Adjudication in a Context of Constitutional Pluralism” (2007) 1 EJLS 1; Lenaerts, supra note 21 at 873.

35. Atkins, supra note 15 at 316; Roper, supra note 18 at 576.

36. Washington v Glucksberg, 521 US 702 (1997), 734.

37. See on this subject Basil Markesinis & Jorg Fedtke, “The Judge as Comparatist” (2005-06) 80 Tul L Rev 11 at 97. In Printz Justice Breyer claimed: “Of course, we are interpreting our own Constitution, not those of other nations, and there may be relevant political and structural differences between their systems and our own. But their experience may nonetheless cast an empirical light on the consequences of different solutions to a common legal problem.” Printz v United States, 521 US 898 (1997), 977.

38. William N Eskridge Jr, “United States: Lawrence v Texas and the Imperative of Comparative Constitutionalism” (2004) 2 ICON 555 at 560. See also Posner & Sunstein, supra note 3 at 139. Some commentators have observed, however, that “the experience from one country might shed minimal light on its possible consequences in another country” since any number of variables could have determined the observed outcomes, not just the law that is being discussed. Annus, supra note 1 at 338. Cf also Mark Tushnet, “The Possibilities of Comparative Constitutional Law” (1999) 108 Yale LJ 1225 at 1307.

39. Mohamed, supra note 17 at para 30.

40. Bratman, Michael, Intention, Plans and Practical Reason (Cambridge: Harvard University Press, 1987) at 180.Google Scholar

41. See Jerzy Wróblewski, “Legal Reasoning and Legal Interpretation” in C Perelman (dir), Études de logique juridique (Bruxelles: Bruylant, 1969) at 9.

42. Ugo Mattei & Mathias Reimann, “Introduction to the Symposium ‘New Directions in Comparative Law’” (1998) 46 Am J Comp L 597 at 597. Approaches to comparative law in legal reasoning can be classified in many different ways according to different explicative purposes: see, among others, Jackson, Vicki, Constitutional Engagement in a Transnational Era (Oxford: Oxford University Press, 2010)Google Scholar; Rosalind Dixon, “A Democratic Theory of Constitutional Comparison” (2008) 56 Am J Comp L 947; Sujit Choudhry “Globalization in Search of Justification: Toward a Theory of Comparative Constitutional Interpretation” (1999) 74 Ind LJ 819; Tushnet, supra note 38. The classification proposed in this paper tries to highlight the normative conditions under which a comparative argument is taken to be sound by courts.

43. See on these issues Pierre Legrand, “How to Compare Now?” (1996) 16 Legal Studies 232; Samuel, Geoffrey, “Epistemology and Comparative Law: Contribution from Sciences and Social Sciences” in van Hoecke, M, ed, Epistemology and Comparative Law (Oxford-Portland: Hart, 2004).Google Scholar

44. Comparative functionalism assumes that “different legal systems give the same or very similar solutions, even as to detail, to the same problems of life, despite the great differences in their historical development, conceptual structure, and style of operation.” Konrad Zweigert & Hein Kötz, An Introduction to Comparative Law (Oxford: Oxford University Press, 1998) at 36. Thus, differences between legal systems are seen as accidents depending on contingent facts; moreover, by looking at the functional properties of regulations one can easily determine which legal solution to the same social problem is “clearly superior” to the others (ibid at 46). See also Mattei, Ugo, Comparative Law and Economics (Ann Arbor: University of Michigan Press, 1997) at 144.Google Scholar

45. Comparative studies characterize these principles and their source in a number of different ways. According to strong comparative cosmopolitanism, for instance, supranational legal principles are a precondition of legal orders, in the sense that their existence makes a legal order conceptually possible or in the sense that compliance with these principles is a precondition of intentional agency, independently of the conception of the good or comprehensive plan of life of the agent. See Peter Häberle, Europäische Verfassungslehre (Baden-Baden: Nomos, 2002) and Claudio Corradetti, “Can Human Rights Be Exported? On the Very Idea of Human Rights Transplantability” in AB Engelbrekt & J Nergelius, eds, New Directions in Comparative Law (Cheltenham & Northampton: Elgar 2009) at 41. On the contrary, weak comparative cosmopolitanism maintains that supranational principles are a result of a deliberation process in which members of a community submit their findings to peer review and mutual checking, such as in the process of scientific knowledge—cf Fedtke, supra note 4 at 82—or that comparative reasoning helps gain insights about moral and political conclusions which are more likely to arrive at a correct decision then a single curt alone: cf Posner & Sunstein, supra note 3.

46. The functional version of universalist theory is invoked in Atkins, supra note 15 at 310. A universalist theory based upon a set of principles common to all jurisdictions is outlined in S v Walters [2002] CCT 28/01 ZACC 6, para 52.

47. The classical source of this normative standpoint is Alan Watson’s theory of legal transplant: see Alan Watson, Legal Transplants: An Approach to Comparative Law (Edinburgh: Scottish Academic Press, 1974). On the basis of his investigation into Roman law heritage, Watson claimed that legal changes generally occur as a result of legal “borrowing” or “transplantation” from one legal order to another, due to the authority and prestige that a certain body of norms assumes toward other legal orders. In this view, legal borrowing characterizes the entire course of legal history and is largely independent from local factors.

48. See Otto Kahn-Freund, “On Uses and Misuses of Comparative Law” (1974) 37 MLR 1 at 7.

49. Cf Printz, supra note 37 at 921, para 11; Stanford v Kentucky, 492 US 361 (1989), 369; Thompson, supra note 27 at 868 (Justice Scalia dissenting); R v Rahey [1987] 1 SCR 588, 639.

50. See, among others, United States v Then, 56 F3d 464 (1995), 469 (Justice Calabresi dissenting); Knight v Florida, 528 US 990 (1999), 997 (Justice Breyer dissenting).

51. Glendon, Mary Ann, Abortion and Divorce in Western Law (Cambridge: Harvard University Press, 1989) at 142.Google Scholar

52. See on this Øyen, Elese, “The Imperfection of Comparisons” in Id, ed, Comparative Methodology: Theory and Practice in International Social Research (London: Sage, 1990) ch 1Google Scholar; Legrand, Pierre, “The Same and the Different” in Legrand, P & Munday, R eds, Comparative Studies: Traditions and Transitions (Cambridge: Cambridge University Press, 2003) at 240.Google ScholarAccording to this normative approach to comparative reasoning, “analogies and the presumption of similarity have to be abandoned for a rigorous experience of distance and difference.” Günter Frankenberg, “Critical Comparisons: Re-thinking Comparative Law” (1985) 26 Harv Int’l LJ 411 at 453. In other words, the purpose of comparison is to “make [its] object ‘strange’ to us.” Jack M Balkin & Sanford Levinson, “The Canons of Constitutional Law” (1998) 111 Harv L Rev 963 at 1005.

53. Dixon, supra note 42 at 961. Cf Tushnet, supra note 38 at 1285.

54. A normative theory of this kind is outlined by Justice Kriger in Du Plessis v De Klerk [1996] (3) SALR 850 (CC), 911-18. For an analysis of this decision see Choudhry, supra note 42 at 859-60.

55. From a pragmatic point of view, such conditions make explicit the commitments that a judge undertakes when using comparative reasoning. By claiming (A1), for instance, a court implicitly commits itself either to (B1) or (B2), and may be asked to fulfil these commitments by claiming (B1) or (B2). If the court does so, this new speech act gives rise to further argumentative commitments as described by the scheme.

56. Alexy, Cf Robert, A Theory of Legal Argumentation. The Theory of Rational Discourse as Theory of Legal Justification (Oxford: Clarendon Press, 1989) ch 3.Google Scholar

57. Robert K Merton, Social Theory and Social Structure (New York: Free Press, 1968) at 477.

58. Schauer, supra note 5 at 1936. In this view, “if there is no way of telling whether an utterance is authoritative, except by evaluating its contents to see whether it deserves to be accepted in its own right, then the distinction between an authoritative utterance and advice or rational persuasion will have collapsed.” Friedman, Richard, “On the Concept of Authority in Political Philosophy” in Flathman, R, ed, Concepts in Social and Political Philosophy (New York: Macmillan, 1973) at 132.Google Scholar

59. Friedrich Schauer, “On the Nature of the Nature of Law” (2012) 98 Archives for Philosophy of Law and Social Philosophy 457. This conception of the nature of law is presented by Schauer as a challenge to the prevalent understanding of the jurisprudential enterprise at present days. According to this understanding, the task of jurisprudence is to identify the essential properties of law: the properties which all legal systems necessarily possess and which define law in all possible worlds. See, for instance, Joseph Raz, “On the Nature of Law” (1996) 82 Archives for Philosophy of Law and Social Philosophy 1; Robert Alexy, “On the Concept and the Nature of Law” (2008) 21 Ratio Juris 281.

60. Cf supra note 20. See on this Judith Resnik, “Law as Affiliation: ‘Foreign’ Law, Democratic Federalism, and the Sovereigntism of the Nation-state” (2008) 6 International Journal of Constitutional Law 33.

61. It is worth underlining that both universalistic theories and reflexive theories of comparative law assume that legal reasons are content-dependent. As Sujit Choudhry has correctly pointed out (see supra note 42 at 870), for universalism “the value of comparative jurisprudence lies precisely in his appeal on substantive principles of political morality.” Similarly, a reflexive approach considers foreign legal norms as useful vehicles for self-reflection “because of the manner in which they reflect and gesture to factual and normative that lies underneath black-letter doctrine.” Thus, to think of legal authority as content-dependent is one of the fundamental ingredients of the contemporary movements in favour of the use of foreign law by courts. From a descriptive point of view, however, the question whether the authority of legal norms depends on their moral or political merits is still open and cannot be discussed here. See on this Paul Markwick, “Law and Content-Independent Reasons” (2000) 20 Oxford J Legal Stud 579; Stefan Sciaraffa, “On Content-independent Reasons: It’s Not in the Name” (2009) 28 Law & Phil 233.

62. Cf Khosla, supra note 29.

63. Schauer correctly points out that optional sources of legal justification are not to be confused with persuasive sources or arguments. Persuasive sources are not authoritative by definition, since their persuasiveness depends on their content and not on their source. On the contrary, optional sources can be content-independent: Schauer, Friedrich, Thinking Like a Lawyer: A New Introduction to Legal Reasoning (Boston-New York: Harvard University Press, 2009) at 69.Google ScholarOn the very idea of persuasive legal source and argument see Bronaugh, Richard, “Persuasive Precedent” in Goldstein, L, ed, Precedents in Law (Oxford: Clarendon Press, 1987).Google Scholar

64. See on this the results of the empirical survey carried out by Gelter & Siems, supra note 1.

65. “In the course of the arguments addressed to us, we were referred to books and articles on the death sentence, and to judgments dealing with challenges made to capital punishment in the courts of other countries and in international tribunals. The international and foreign authorities are of value because they analyse arguments for and against the death sentence and show how courts of other jurisdictions have dealt with this vexed issue.” Makwanyane, supra note 17 at para 34.

66. Makwanyane, supra note 17 at para 34.

67. On the use of comparative reasoning by the ECtHR see Alec Stone Sweet, “A Cosmopolitan Legal Order: Constitutional Pluralism and Rights Adjudication in Europe” (2012) 1 Global Constitutionalism 53.

68. The fact that a foreign ruling provides content-independent reasons for domestic adjudication does not make it a legally authoritative pronouncement in the domestic legal order: not every content-independent authority is a legal authority, nor can the practical authority outlined here be seen as a moral authority. Cf Raz, supra note 20 at 270.

69. As Richard Bronaugh has pointed out (supra note 63 at 247), “persuasive precedents are powerful and fair instruments of invention because, when convincing, they will show ways in which—again rationally and in all fairness—the fetters of binding precedent can be slipped.”