II. Persuasive authority and theoretical authority

Judges almost uniformly refer to foreign law as holding only persuasive authority. There has been a signal failure, however, to provide a convincing account of what this means. Some argue that foreign law can and should have no authority.^{Footnote 10} Others argue that since the authority is only persuasive, the practice cannot be problematic.^{Footnote 11} Yet others hold that if foreign law relies on suasion for its effect, then it is not authoritative in any sense and is no different from anything else on which a court might rely.^{Footnote 12} What these positions have in common is that they seek to avoid, rather than dissolve, the paradox apparently involved in the notion of persuasive authority. Other theorists have grappled more directly with that paradox.

Waldron equates the persuasive authority of foreign law with the authority accorded to non-binding precedents of national law. He argues that persuasive authority has less force than binding authority but still some force independent of its persuasiveness.^{Footnote 13} Arguments thereby have weight that is partly a function of their persuasiveness and partly a function of their source.^{Footnote 14} Although this is plausible as an account of the persuasive authority accorded to national sources (for instance, courts of coordinate jurisdiction), it does not easily fit the ways in which national courts treat foreign law in constitutional cases. In such cases, there is little (if any) evidence of judges treating foreign case law as imposing any sort of obligation to act in a particular way, still less an obligation that could lead a national court to disapply an obligation under national law to opposite effect. Sedley observes that he knows of no judge in the world who has ever decided a case differently because of persuasive authority in other jurisdictions.^{Footnote 15} If this is correct, Waldron’s account of the persuasive authority of foreign law cannot hold.

Glenn has characterized persuasive authority as authority that attracts adherence as opposed to obliging it.^{Footnote 16} However, this fails to provide any discrete meaning to the word ‘authority’. For that reason, Schauer argues that persuasive authority is a contradiction in terms.^{Footnote 17} The point of authoritative statements is that their normative force is content independent. If an army sergeant issues a directive, her subordinates are taken to be under an obligation to obey that directive, wholly irrespective of the merits of its contents. In contrast, the notion of persuasion implies scrutiny and consideration of merits. The same directive therefore cannot rely for its force simultaneously on authority and suasion. To resolve the problem, Schauer suggests that it is more helpful to think in terms of ‘optional authority,’ as capturing the distinction between that which must be used and that which may be ignored.^{Footnote 18} The phrase ‘optional authority,’ however, remains problematic. If we can opt in to treating something as authoritative, how can it really be authoritative?

The apparent contradiction in the term ‘persuasive authority’ can be resolved in the context of the citation of foreign law in constitutional cases if we pay attention to the distinction between practical authority (with a view to action) and theoretical authority (with a view to knowledge). Some argue that where a legal system exists, the law of that system will either claim to have or be taken to have legitimate, practical authority.^{Footnote 19} The kernel of legitimate, practical authority is that the directives of the authority both provide reasons for the subjects of authority to behave in a particular way and exclude the force of such reasons as might, absent the authoritative directive, have applied. Legitimate, practical authority is – in this image – absolute. However, the mere fact that law makes this claim or that people treat law this way cannot establish that law is legitimately practically authoritative. Justifications of practical authority usually rely on the authority having either greater wisdom or the ability to solve coordination problems that need to be solved.

Foreign law does not claim authority in the national legal system, but – as noted above – judges often speak of it as having authority.^{Footnote 20} We can dissolve the paradox of persuasive authority if we conceive of judges treating foreign case law as theoretically authoritative rather than practically authoritative. In the same way that practical authority provides an exclusionary reason for action, theoretical authority provides an exclusionary reason for belief. If we treat another person as a theoretical authority, we treat the fact of her belief in X as a reason to believe X, that excludes the force of other reasons we might have to believe or disbelieve X. I have reason to accept that global warming exists and is caused (at least substantially) by human activity because of the fact that the vast majority of climatologists think so and they hold theoretical authority over me on this issue. Furthermore, this authority excludes as irrelevant any half-baked assessment of the climate that I might be inclined to make myself. In much the same way, if in Cork, I have reason to believe that what a Cork person tells me about the location of Kent train station is correct.

The justification for theoretical authority can only be the justification of greater wisdom, not the justification of coordination. Unlike practical authority, therefore, the justification of theoretical authority (greater knowledge) matches the object of theoretical authority (knowledge). Whereas practical authority can require one to act in a way that one knows is ill-advised, theoretical authority does not require us to believe what we know we have greater reason to disbelieve, because familiarisation with the reasons for belief and disbelief simultaneously eliminates the gulf in wisdom and displaces the theoretical authority. Let us reconsider the two examples. In the unlikely event that I were to develop great expertise on global warming, I would have no reason to accept scientists’ views as authoritative but could instead accept or reject their opinions based on my own assessment of the merits. Similarly, if in Cork I were to consult a map and realise that the train station lay in the opposition direction, I would simultaneously have no reason to treat the Cork person as theoretically authoritative over me in respect of the location of the train station and reason to disbelieve what she had told me about the location of the station (presumably motivated by the antipathy that many Cork people hold for Dubliners). The relative difference in knowledge that grounded the theoretical authority in the first instance has been displaced by my consultation of the map.

Of course, there will usually be more than one possible authority figure in respect of a particular issue. Not all scientists agree about climate change. However, given the norms of scientific knowledge, we have reason to treat 95 per cent of scientists as theoretically authoritative rather than the other five per cent. A more difficult situation could arise where I need to understand a passage of Aristotle that has been translated differently by two eminent classicists, each of whom holds theoretical authority over me. If I seek other translations, that intensifies rather than resolves the problem. Other than make an act of faith, the only way out of this quandary would be to engage with the issue myself and explore the reasons why each authority figure offers her particular translation. Over the course of this process, each classicist’s theoretical authority would dissipate. But the views of each would have played a special role in my reasoning process on account of their initial theoretical authority: I would be grappling with their understandings of Aristotle rather than attempting a blank-slate translation of Aristotle.

Theoretical authority is therefore best understood as providing an exclusionary reason to believe X unless and until one has as good a claim to knowledge or perspective as the authority. The views of the theoretical authority figure play a special role in that reasoning process: they provide a starting point, a guide and a foil for analysis. The same occurs where there is more than one authority figure. Countervailing reasons are not weighed against the exclusionary reason, but greater appreciation of all reasons by the subject of authority dissipates that authority and makes it rational for the previous subject of authority to assess the balance of reasons herself.

It is possible to have theoretical authority about directives that are taken to be practically authoritative. For instance, I have no practical authority when it comes to interpreting Irish constitutional law, but I do have knowledge of Irish constitutional law and I hold theoretical authority over at least some people in respect of Irish constitutional law. If a foreign court needed to establish what protections Irish constitutional law provided to an accused person before determining an extradition request from Ireland, as an expert witness I would have relative (at least before cross-examination and the examination of other expert witnesses) theoretical authority as to Irish constitutional law. But I would have practical authority for neither the judge nor the litigants. My authority is limited to the question of what legal concepts might mean, not what individuals ought to do in light of those concepts.

Foreign case law can be understood as theoretically authoritative as to the meaning of national constitutional provisions in an analogous way, albeit with important differences: the fact of it being a judgment of a foreign court is taken to provide a reason for the national court to understand its own legal concepts in a particular way. The knowledge of foreign judges is akin to the classicists’ knowledge of Aristotle rather than the scientists’ knowledge of climate change. It is less about empirically identifiable facts but more about judgment and discernment, although those qualities also play an important role in scientific knowledge. It is an applied knowledge of what moral and legal values mean for particular situations; this knowledge can be helpful to judges in other countries seeking to understand what similar values mean for similar situations. If we conceive of foreign law as theoretically authoritative in this way, it avoids Scalia’s objection: consideration of foreign law can help judges better understand the laws of their own system, but foreign law never has direct relevance to the question of what the judge ought to do.

The concept of theoretical authority also shows how foreign law can enrich judicial decision-making. Some have argued that foreign law is persuasively authoritative in the same way as all other non-binding sources, such as law review articles. As such, for Tushnet and Jackson, the use of foreign law is not a sui generis issue and its legitimacy or otherwise turns on the resolution of other debates in constitutional theory.^{Footnote 21} This position is insensitive to differences between the treatment often afforded to foreign law and the treatment generally afforded to other factors, national law provisions aside, that might bear on a judge’s decision-making process. It is easier for counsel to cite and judges to rely on foreign case law than it is for counsel to cite and judges to rely on law review articles or the works of moral philosophers. In the United Kingdom, the official law reports list foreign cases alongside national cases but do not list any other sources that might have been cited. These observations are impressionistic and open to contradiction. It is worth noting, however, that Flanders has reached the same conclusion in respect of the US legal system.^{Footnote 22}

This sense of how foreign law is treated coheres with the theoretical authority concept. Foreign law is treated as authoritative simply because it is foreign law. The foreign law holds theoretical authority at the outset and provides a starting point, guide and foil for the national judge’s reasoning process. This applies especially where the national judge considers potentially conflicting foreign authorities. However, this theoretical authority dissipates as the national judge undertakes her own examination of the issues. Ultimately, foreign law ceases to be treated as authoritative and instead persuades only on its merits. However, before the national court undertakes that reasoning process (and indeed if the national court were not to undertake that process), the foreign law would be treated as authoritative irrespective of its persuasiveness. This is not the case of law journal articles and the musings of moral philosophers, the influence of which depends entirely on its persuasive effect. The concept based on theoretical authority thus makes sense of the prevalence of the phrase ‘persuasive authority’ in a way that avoids Scalia’s objection while making sense of Bingham’s claim that consideration of foreign law enriches the judicial decision-making process.

III. Theoretical authority and judicial learning

The concept based on theoretical authority also makes sense of the idea of judicial learning, often used by academics and judges writing extrajudicially to explain their use of foreign law. Ackermann writes of judges ‘seeking information, guidance, stimulation, clarification, or even enlightenment, but never authority binding on one’s own decision’.^{Footnote 23} Markesinis and Fedtke speak of Ackermann infusing the South African legal system with a ‘treasure trove of potentially useful foreign ideas’.^{Footnote 24} Slaughter writes that judges accept the value of persuasive rather than coercive authority; they acknowledge the possibility of learning from one another based on relative experience with a particular set of issues.^{Footnote 25} Jackson comments that decisions of foreign courts can inform national courts ‘not only by suggesting ways of reasoning about common areas of human experience, but also by providing a basis against which divergent judgments can be tested’.^{Footnote 26} Jackson also suggests that consideration of foreign law can open up ways in which national law can be re-understood or reconstructed as part of the ongoing process of constitutional development.^{Footnote 27} Breyer observes that the practice ‘involves opening your eyes to what is going on elsewhere, taking what you learn for what it is worth, and using it as a point of comparison where doing so will prove helpful’.^{Footnote 28}

Markesinis and Fedtke emphasise that consideration of foreign law does not absolve judges from forming their own opinion, a point consistent with the treatment of foreign case law as holding theoretical authority.^{Footnote 29} Judges who engage with foreign law almost uniformly emphasise this limitation. In Roper v Simmons, O’Connor J of the US Supreme Court was prepared to have regard to the international consensus but would not allow it displace the view she had reached about the state of national consensus and other issues in the case.^{Footnote 30} Justice Hoffmann-Riem of the German Constitutional Court writes that learning from other legal orders does not shift the responsibility for the decision onto the other order; legal solutions must be rooted in the order to which they apply.^{Footnote 31} Sometimes, judges present this point as an opposition between authority and learning. Bader-Ginsberg has stated that foreign opinions are not authoritative but ‘can add to the store of knowledge relevant to the solution of trying questions’.^{Footnote 32} This opposition is only necessary if one conceives of authority in terms of practical authority. Once one conceives of the persuasive authority of foreign law as theoretical authority, all tension between authority and learning dissolves.

The judgment of Chaskalson P of the South African Constitutional Court in The State v Makwanyane provides a good illustration of judicial learning and the treatment of foreign case law as theoretically authoritative.^{Footnote 33} In one of the first cases to come before it, the Court had to consider the constitutionality of the imposition of the death penalty for murder. The recently enacted interim South African Constitution did not directly address the issue of the death penalty but contained several provisions that were relevant to the issue. Section 11(2) provided that no person should be subjected to cruel, inhuman or degrading treatment or punishment. Section 9 guaranteed the right to life. Section 10 guaranteed respect and protection of dignity. Section 8 guaranteed the right to equality before the law and equal protection of the law.

Chaskalson P referred to a wide range of foreign material, which he referred to as ‘authorities’. Foreign law was cited not just for its relevance to the substantive issue, but also for its assistance on the more technocratic problems of constitutionalism, such as the relevance of travaux préparatoires and how to approach limitation provisions. The judgments of the German Bundesverfassungsgericht were particularly important in this regard. On the substantive issue, Chaskalson P reviewed case law from Hungary, the USA, Canada, the ICCPR, the ECHR, India, California, Massachusetts, and Tanzania. He described these as valuable ‘because they analyse arguments for and against the death sentence and show how courts of other jurisdictions have dealt with this vexed issue’.^{Footnote 34} Four basic positions emerged. Courts in Hungary, California and Massachusetts had prohibited the death penalty, Hungary on the basis of the right to life, the two US States on the basis that it was impermissibly cruel. Courts in India and Tanzania had upheld the constitutionality of the death penalty. The USA had upheld the constitutionality of the death penalty but surrounded its practice with many procedural guarantees. This led to death row phenomenon, which in turn caused different levels of difficulty for Canada, the UNHRC and ECtHR when considering possible extraditions to the USA.

Chaskalson P treated this case law as the starting point for his analysis, carefully interrogating the reasoning behind those conclusions and tracing both similarities and differences between the various constitutional texts and regimes and the South African Interim Constitution. He rejected the US approach because of the endless litigation, considerable expense and interminable delays caused by using procedural fairness to mediate the contradiction between allowing the death penalty in principle while accepting that it might amount to cruel and unusual punishment in particular circumstances.^{Footnote 35} The conclusions reached in the foreign cases provided possible positions on the question of whether the death penalty should be prohibited. In using these as the starting points for his analysis, Chaskalson P treated the foreign case law as theoretically authoritative. The positions recommended themselves to his consideration simply because they had been reached by other courts. However, as he engaged in the issue himself, the theoretical authority of the foreign case law dissipated. Ultimately, the foreign case law could only persuade on its merits, the chief question being its appropriateness to the South African context. Chaskalson P had also noted that foreign law would be particularly important in the early stages of transition where there is no developed indigenous jurisprudence.^{Footnote 36} This illustrates the two dimensions of the theoretical authority concept as applied to the use of foreign case law: the relative gap in wisdom that warrants theoretical authority applies both when a court approaches a new issue for the first time and, more generally, when a new court starts to approach constitutional issues for the first time. This explains why we tend to see greater reliance by new courts on foreign case law.^{Footnote 37}

Many have employed the phrase ‘judicial dialogue’ rather than judicial learning to conceptualise the judicial use of foreign case law in constitutional cases. L’Heureux-Dubé writes of courts involved in judicial dialogue, looking to one another for persuasive precedent.^{Footnote 38} The word ‘dialogue’, however, does not seem a good fit for the practice under discussion. Dialogue would involve judges speaking directly to one another. Court A must understand its judgments as being primarily addressed to court B, and vice versa. There is little evidence to suggest that courts understand their judgments in this way: written judgments and extrajudicial commentary both assume that judgments are primarily addressed to the parties in the case. This is consistent with the model of judicial decision-making stipulated at the start of this article. In a judicial survey, Flanagan and Ahern did not directly ask whether apex court judges considered themselves in dialogue with foreign judges; however, through combining the responses to two questions, they conclude that nearly half of their respondents perceive distinguished foreign judges as part of the audience for their judgments.^{Footnote 39} Even if this is correct, however, it does not amount to judges engaging in a dialogue with foreign judges. What these references gesture towards, however, is an increasingly prevalent practice of reciprocal listening: court A has regard to the case law of court B while court B has regard to the case law of court A. This is not judicial dialogue, however, since neither court understands its judgments to be addressed primarily to the other.^{Footnote 40}

‘Judicial dialogue’ is also used to describe a process in which national judges use foreign law to identify and interrogate the presuppositions of their own system. In this vein, Choudhry provides a perceptive account of what he terms a dialogical use of foreign law, by which he means that national courts carefully scrutinise foreign law to identify similarities and differences. They can use foreign law to emphasise the particular in their own system or to stimulate change. But he never suggests that the dialogic mode actually involves judges engaging in a dialogue with one another.^{Footnote 41} Judicial dialogue in both Choudhry’s sense and the reciprocal listening sense are better understood as variations of theoretical authority: these accounts enhance our understanding of the different ways in which judges can learn from foreign law. However, the currency attained by the term ‘dialogue’ is unfortunate because it suggests a wholly different process in which judges use their judgments not primarily for the purpose of resolving the case before them but instead for the purpose of engaging in interjurisdictional dialogue. Such an approach would negate the entire basis for treating foreign law as theoretically authoritative in the first place which, as the next section explains, depends on the fact that a judgment is an attempt to resolve a real-world dispute, not an abstract philosophical exegesis.

IV. The justification for treating foreign case law as authoritative

The most strident criticism of the reliance on foreign law in constitutional cases wrongly assumes that the foreign law is treated as practically authoritative, i.e. as having direct normative force within the national legal system. In Roper v Simmons, Scalia J of the US Supreme Court described the premise of the majority’s argument as being that ‘American law should conform to the laws of the rest of the world’.^{Footnote 42} If judges treated foreign law as practically authoritative, they would have to give it real normative weight that could pull against and potentially override a normative direction democratically endorsed within their own system. This would involve the exercise of judicial power on the basis of standards that are not democratically revisable. The treatment of foreign law as theoretically authoritative is fundamentally different. It does not impose any obligation on the national court to act in accordance with the law of the foreign country. This is consistent with the extrajudicial observation of Sedley that he knows of no judge in the world who has ever decided a case differently because of persuasive authority in other jurisdictions.^{Footnote 43} Once foreign law is being used only to help understand national law concepts, there can be no significant democratic objection to the practice.^{Footnote 44} With this most fundamental criticism out of the way, the justification of the practice can be considered.

Justification for theoretical authority depends on relative gaps in knowledge or wisdom. Climatologists, Corkonians and classicists hold theoretical authority over most other people in their relevant area of expertise. If one comes to know as much as, or more than, the person who held theoretical authority, there is no longer any justification to treat that person as theoretically authoritative. Even if one accepts the views of the previously authoritative figure, one does so because one is persuaded by their merits rather than compelled by authority. The same sort of observation can justify national courts treating some types of foreign law as authoritative in some circumstances. A foreign court’s understanding of the meaning and appropriate application of a legal concept at the end of a case should be stronger than the national court’s understanding at the start of a case. This analysis does not of itself justify treating foreign law, more so than law review articles, as theoretically authoritative. The final step in the argument turns on the special nature of court processes for adjudication.

A judgment is written only after the judge has the benefit of hearing arguments advanced by (at least) two reasonably well-funded opponents. Each side has the opportunity to deconstruct the other side’s argument, as does the judge. Moreover, the judge (conscious that the judgment will have real world effects and is not simply a philosophical teaser) can be assumed to have taken care in coming to her judgment.^{Footnote 45} Developing on this idea, Jackson suggests that the judgments of national courts have more weight than judgments of international tribunals, since they have binding effect and the judge lives in the country where that effect will take place.^{Footnote 46} Taken together, these features justify theoretical authority for foreign case law in a way that does not apply to other forms of foreign law or to other non-binding sources such as law review articles. As such, the justification coheres well with the general contours of judicial practice.

There are, however, four significant limitations on this justification. First, the theoretical authority is temporally limited since the national court is embarking on the same process that the foreign court has already completed. Once the national judge starts to approach her own reasoned conclusion about the legal problem before her, the foreign case law loses its justified authority and has only the force of persuasion. In the same way as the theoretical authority of climatologists, Corkonians and classicists dissipates once the subject of authority gains as much knowledge, so the theoretical authority of foreign case law dissipates once the national court has equalized the knowledge base by going through the same judicial process that justified the theoretical authority of the foreign court in the first instance. The theoretical authority of foreign case law provides a starting point, guide and foil for analysis, but thereafter its force depends on its persuasiveness.

Second, and related to this, a national court should not artificially preserve the justified theoretical authority of foreign case law by refusing to engage in its own reasoning process. D v Ireland is an example of this.^{Footnote 47} The Irish Supreme Court upheld the constitutionality of the Criminal Law (Sexual Offences) Act 2006, which criminalised a wide range of sexual activity with persons under the age of 17, but exempted from criminal sanction females under the age of 17 who engaged in vaginal intercourse, as distinct from the other criminalised forms of sexual activity. The Supreme Court did not cite any of its own case law on the Irish Constitution’s guarantee of equality, which suggested some heightened scrutiny for sex-based discriminations. Instead, the Court relied on the judgment of the US Supreme Court in Michael M v Superior Court of Sonoma County, which upheld the constitutionality of a law that made it unlawful for a male to have sexual intercourse with a female under the age of 18.^{Footnote 48} Denham CJ, delivering the judgment of the Court, adopted the rationale of Rehnquist J to the effect that discrimination in favour of females would provide an incentive for females to report the offence, which in turn would deter males from committing the offence, which in turn would reduce the risk of teenage pregnancy, the core objective of the Act. The difficulty is that this rationale does not carry over to the Irish Act in question, given that it also criminalizes for both males and females a wide range of other sexual acts in which – the evidence suggests – teenagers tend to engage.^{Footnote 49} In that context, the exception from criminal liability for females who engage in vaginal intercourse actually creates an incentive for young females to put themselves at risk of pregnancy rather than engage in other sexual activity for which they might be criminally liable. We can understand this in terms of the Irish Supreme Court continuing to treat the previous judgment of the US Supreme Court as theoretically authoritative after that authority should have been displaced by the Court’s own consideration of the issue. This led the Court to overlook some important differences between the two cases. A danger with the use of foreign case law is that it lends itself to overuse in this way. Because foreign law is framed in the same language of practical authority that the national court will use to decide its case, there is always the risk that the national court may treat it as practically authoritative.

Third, for the limited justification for theoretical authority to hold, the foreign court must be in a similar legal system, interpreting a similar constitutional position and addressing a similar problem. Writing extrajudicially, some judges, such as Ackermann, note the universalist character of modern constitutions;^{Footnote 50} other judges make the more modest claim of commonality between some constitutions.^{Footnote 51} These are taken to be preconditions for comparison. Of course, it may transpire that an initial apparent similarity is not real. This is not problematic provided the national court approaches the foreign law with care, bearing in mind that the courts’ role is not simply to resolve great social disputes over liberty, equality and fraternity, but rather to resolve those disputes according to some set of constitutional material.^{Footnote 52} This is not to argue that only similarities between jurisdictions are relevant. As noted above, Choudhry and Jackson have both shown how courts can learn from differences as much as similarities. However, there must be a baseline of commonality before comparison is helpful. The constitutional case law of Saudi Arabia is probably not a useful comparator for a Western liberal democracy seeking to understand a gender equality issue, and vice versa.

Fourth, this is a justification for reciprocal judicial learning and cross-jurisdictional comparison, but not for interjurisdictional judicial dialogue. As discussed above, the term ‘judicial dialogue’ is generally taken to mean reciprocal judicial learning or a process of the court scrutinising its own legal material in the light of the positions adopted in foreign law. However, some academic literature and extrajudicial writing encourages judges to engage in judicial dialogue in the sense of speaking directly to foreign courts. Markesinis and Fedtke muse:

Some see the promotion of judicial dialogue as justification for having regard to foreign law. Slaughter argues that judges perceive themselves as engaged in a common endeavour that transcends national boundaries – this ‘creates an incentive to both lender and borrower be’.^{Footnote 54} O’Connor offers a justification for judicial dialogue by suggesting that the US courts should cite foreign case law in order to create ‘that all-important good impression’ and enhance the ability of the US to act as a rule-of-law model for other nations.^{Footnote 55} Similarly, Breyer has suggested that the US Supreme Court should refer to judicial decisions in emerging democracies in order to bolster those democracies.^{Footnote 56} Although these are noble sentiments, they are inconsistent with the very basis on which foreign law can be treated as theoretically authoritative in the first instance. Paying attention to how her judgment will be received in foreign countries introduces a tension with the judge’s primary obligation to decide a case based on norms democratically endorsed in her own legal system for the benefit of the litigants and her own community. The tension may well be resolved in favour of the judge’s primary obligation (as indeed was the case in Justice O’Connor’s judgment in Roper v Simmons discussed above), but it would be far better if the tension were not introduced in the first place. The theoretical authority of country A’s case law for the judges in country B depends on that case law being an attempt to resolve a dispute in country A not an attempt to fashion a cosmopolitan value for export to country B.

V. The dangers of treating foreign case law as authoritative

There is therefore a pro tanto justification for judges treating foreign case law as theoretically authoritative, subject to significant limits that flow from the nature of the justification itself. However, there are also two counterarguments that tend to undermine the force of that justificatory argument. The first turns on the selection criteria to be applied when deciding which foreign case law to refer to. The import of the justification for treating foreign case law as theoretically authoritative in the first instance is that the judgments of all courts that share those desirable structural requirements are equally theoretically authoritative. If only some of those courts are referred to, what selection principle is used? The national court will probably do one of two things: reach for those foreign cases that are most easily available (presumably those available on the internet with a version in the judge’s own language, ideally from a legal system with which the judge has some familiarity) or seek out those cases that support the conclusion that the judge wishes to reach.^{Footnote 57} Either way, there is a significant bias in the selection principle. It could be argued that if judges behave with such intellectual dishonesty, there is a general problem of judicial ethics not peculiar to the foreign law debate. However, the particular way in which foreign case law is treated as theoretically authoritative means that the concerns remain valid. Because foreign case law, on account of its theoretical authority, has some force independent of its ability to persuade (unlike other non-binding sources), a selected set of foreign case law is likely to be treated as more relevant than the intrinsic merit of the arguments contained in that case law would suggest. The manner in which it is selected therefore remains critical.

The second counterargument turns on the difficulty of properly understanding the laws of a foreign legal system. In this regard, Jackson has helpfully coined the phrase ‘bilegalism’.^{Footnote 58} In order to understand the case law of a foreign legal system, it is necessary to understand both the surrounding legal context and the legal culture in which it is placed. Behind most constitutional judgments lie layers of assumptions about the constitutional text, precedent cases and attitudes to judicial deference. These are difficult enough to gauge when one has spent a professional life studying that legal context and living in that legal culture. It is far more difficult when one is an occasional visitor to a legal system. Various strategies have been suggested to counteract this problem. Law Schools could become more proficient at teaching comparative law; lawyers and judges would become more versed in the laws of foreign legal systems; academia could be called on to provide evidence as to the law in foreign countries.^{Footnote 59} As admirable as these developments might be, they seem either impractical or excessively costly. Law students would not have to study comparative law so much as the foreign law of many other legal systems (at least 40 or 50 if the selection bias principle is not to be replicated). The knowledge base of many lawyers largely crystallises, outside their areas of practice, at the point at which they completed formal education. There is little reason to think that this would be different in relation to the laws of other legal systems, which would remain unconsidered until the lawyer was involved in relevant litigation. To ensure accurate and properly tested evidence of foreign law would be costly both in terms of preparation and court time. The prospect of reaching a better judgment scarcely justifies the delay and expense.^{Footnote 60} The cost implications might instead lead to the task not being done properly, reintroducing the problem of selection criteria.

The general justification for treating foreign case law as theoretically authoritative is undermined by these two counterarguments. However, the counterarguments are contingent. In a particular case, a judge might employ a reasonable selection principle. In a particular case, a judge might know enough of the foreign legal system properly to understand the case in question. Nevertheless, there is good reason to consider that these contingencies are likely to occur. Ultimately, the question of whether reference to foreign law is appropriate is highly context-specific. The desirability of referring to foreign law is a function of two factors: the limits of the justification for referring to foreign case law at all and the strength of the considerations militating against reference.^{Footnote 61} These considerations will vary from case to case. The purpose of this article is not to offer a set of bright-line rules, but a number of general points may be made.

First, most constitutions are both contingent and universalist in character. Where a foreign constitution is a contingent response to a local problem, reference to its case law is less appropriate. Where a foreign constitution commits itself to a universal ideal shared by the national constitution, reference to its case law is more appropriate. Many commentators have suggested that reference to foreign law is inappropriate in cases concerning federalism and distribution of governmental powers. Jackson argues that constitutional provisions about federalism are more likely to be the result of historic compromise.^{Footnote 62} Kentridge has commented that ‘separation of powers’ is an international catchphrase but it means different things in different counties.^{Footnote 63} Conversely, most agree that the more universalist human rights provisions provide a better case for comparison. This cannot be simply assumed, however, and should be verified. For example, in one sense, both the US Constitution and the ECHR protect property rights. But a prohibition on the taking of private property for public use without just compensation cannot be assumed to be the same as an entitlement to the peaceful enjoyment of possessions, subject to various exceptions. Any reliance on foreign case law must therefore take great care to ensure that like is being compared with like and/or that lessons are only being drawn from relevant differences.

Second, the most appropriate type of constitutional case for reference to foreign law is one of judicial method. The processes of constitutional litigation produce problems that are generally unanticipated in the constitutional text and best seen as technocratic lawyering issues. The two most obvious of these are questions of standing and the effects of a declaration of unconstitutionality. In this type of case, the problems of misunderstanding are lowest and it is safest to take the foreign case law at face value. There can still be latent differences, however. Federalism may affect the foreign court’s judicial review power in unanticipated ways. A textual ‘case or controversy’ provision may imply a stricter approach to standing. Limitation issues, particularly given the widespread adoption of ‘proportionality’ tests, might be thought a safe arena in which to learn from foreign case law. However, in this context, judicial attitudes of deference to elected organs of government are most important and also most difficult to identify. These attitudes are seldom discernible from the explicit comments of judges in any one case but rather can only be identified with a thoroughgoing knowledge not only of constitutional case law but also the unspoken norms and conventions that govern a particular legal community.^{Footnote 64} Learning from foreign case law is at its most fraught in this context and should be avoided.

Third, where there are genealogical connections between different constitutions, the similarity between the provisions is likely to be greater and the justification for having regard to foreign law stronger. For instance, where the judicial committee of the Privy Council interpreted the constitutions of former colonies – all drafted on similar lines – cross-comparison of the case law from the different jurisdictions was appropriate.^{Footnote 65} The same applies where constitutions share provisions derived from the Universal Declaration of Human Rights and mediated through the ICCPR or ECHR.^{Footnote 66} Nevertheless, over time each country’s approach may have become encrusted with different judicial attitudes, meaning that judicial learning still requires great care.

VI. Other justified uses of foreign law

The claim of this article is that the central case of the use of foreign law involves judges treating foreign case law as theoretically authoritative. In general, the more the practice departs from the central case, the less justified it is likely to be. However, there are at least two other ways of using foreign law that may be justified. First, courts sometimes refer to foreign law in constitutional cases not as theoretical authority for what a provision of national law might mean but rather as direct evidence of the possible effects of a particular course of action. A good example of this is the judgment of Rehnquist CJ of the US Supreme Court in Washington v Glucksberg.^{Footnote 67} Upholding the state’s criminal prohibition of assisted suicide, Rehnquist CJ referred to reports from the Netherlands to substantiate the concern that, despite precautionary measures, there was a tendency for a relaxation of a ban on assisted suicide to lead to pressure on vulnerable persons and less than fully voluntary euthanasia. Under this approach, the Dutch experience had no greater or lesser weight than, say, empirical evidence about how a particular practice might have fared in the court’s own jurisdiction. Many of those within the US generally sceptical about reliance on foreign law do not see this practice as problematic, perhaps because it does not involve the notion of authority.^{Footnote 68} This practice is justified if the foreign law in question does, in fact, provide relevant evidence.

Second, a legal system may develop a constitutional rule that regard must be had to foreign law as an aid to understanding certain provisions of national law. Rules of this type tend not to distinguish between foreign case law and foreign law. What is important is the position actually adopted by foreign legal systems rather than learning from any process of judicial reasoning. For instance, as a matter of US constitutional law, the phrase ‘cruel and unusual punishment’ in the Eighth Amendment is to be interpreted with reference to the evolving standards of decency that mark the progress of a maturing society. Jackson traces the practice of having regard to foreign law to an 1859 case upholding execution by firing squad in the Utah territory.^{Footnote 69} In Roper v Simmons, Kennedy J, delivering the judgment of the majority of the US Supreme Court, prompted much of the controversy in the US on this issue by making extensive references to foreign and international law on the legitimacy of the execution of adults for crimes committed when minors.^{Footnote 70} Foreign law, national consensus and psychological literature were interpreted alongside one another, all leading the majority to conclude that the practice amounted to cruel and unusual punishment. The fact of being foreign law led those judges to treat that foreign law as evidence of contemporary standards of decency, rather than as theoretically authoritative in relation to the meaning of cruel and unusual punishment. The legitimacy of this approach is a doctrinal and interpretative question for specific legal systems.