Comparative law arguments are found in a very small percentage of decisions of supreme courts, yet Bobek argues that they play an important role in judicial reasoning when filling gaps in the law. The great merit of this book is that it encourages the reader to rethink his or her expectations about the place of comparative materials within judicial reasoning. Common lawyers, especially, would expect that an argument which played a significant part in reaching a decision would feature explicitly in the reasoned judgment. The absence of material from a judgment would indicate its lack of significance. The advantage of Bobek's study is to suggest that expectations about the place of comparative materials within published judicial reasoning need to be adjusted to fit within the paradigms and traditions of particular legal systems. Furthermore, Bobek also forces the reader to rethink the place that comparative arguments might reasonably be expected to play in any legal system. Such arguments will not be decisive on their own in leading courts to depart from the solutions which internal sources would justify. But that does not mean that they are insignificant.

The first valuable contribution that Bobek makes is to clarify what counts as a ‘comparative’ argument. He distinguishes between ‘mandatory’ arguments, eg the application of a foreign system in private international law or in application of a treaty, and ‘non-mandatory’ arguments, where the judge has discretion what to cite. Judges are seeking inspiration, not authoritative reasons, and so the category of non-mandatory arguments constitutes the focus of his research. Mere citation is not comparison. Citation can be a mere adornment to a judicial argument, or a polite acknowledgement of the work of counsel or judicial assistants. Bobek is concerned to focus on situations in which there is sufficient engagement with the arguments of a foreign legal system that it constitutes one of the reasons for the instant court's decision. Now Bobek rightly points out that this is quite difficult to research. First, the articulation of reasons for decisions is more elaborate in some systems than in others. If the comparative reasons are not essential, but supportive (as Bobek convincingly explains), then they might well be omitted in a system whose judgments focus only on necessary reasons for decisions. Secondly, practical considerations affect whether a court can really make use of these reasons. Do the deciding judges have time to look at the materials or to understand their legal context? Are not judges likely to be criticized for ‘cherry-picking’ in their choice of material from another system? In even supreme courts with a very large throughput of decisions, the discussion of ancillary reasons for decisions is a luxury. Thirdly, evidence is only readily available about ‘institutional’ reasons, ones provided within judgments or formal preparatory materials. Bobek helpfully identifies the importance of transnational judicial networks (more fully explained by Monica Claes and Maartje de Visser) as vectors of influence, but it is hard to detect their influence. Rather, he demonstrates the importance of scholarly legal writing as an important intermediary. This saves judicial research time; but, more importantly, it provides reassurance that a particular foreign case or outcome is soundly based in the other system and can be explained in relation to other parts of the legal system. So judges will rely on scholarly works, rather than researching or citing original foreign sources.

Bobek's second valuable contribution is to explain why judges resort to foreign legal arguments. Legal systems may be ‘dogmatically closed’ (197) at particular times for political reasons, or because judges are not supposed to play a creative role, or simply because the kinds of gaps in the legal system do not lend themselves to the worthwhile use of this material. But when legal systems are in flux or where significant gaps appear, then the use of comparative law becomes more frequent. Bobek demonstrates that there is no fixed pattern of using comparative materials in legal systems—their use changes over time and circumstances.

Bobek contributes distinctively to the existing literature by his case studies of legal systems. He studies two blocks of systems. On the one hand, England, France and Germany are studied by providing a synthesis of existing studies of judicial practice, theoretical and empirical, confirmed by a very limited sample of recent judicial decisions in supreme courts. Inevitably, the French chapter lacks good empirical data, and readers will need to supplement this by analysing some of the conclusions of the public representative and the report of the reporter judge, which are now online. The synthesis is good and brings out the similarities and differences between the systems more clearly and insightfully than in many comparative studies. On the other hand, his very distinctive empirical study of Slovakia and the Czech Republic as representative of Central and Eastern European legal systems brings out the importance of institutional context and practices, as well as historical tradition. There is sufficient diversity in these examples to suggest lines of reflection on the way in which comparative law is used in different legal systems. It will be for others to expand the range of countries and modify the analysis. But the suggestion that there may be differences between human rights decisions and other branches of law encourages the reader not to treat a legal system as a monolithic whole.

The work is very readable. The empirical chapters are preceded by substantial chapters which analyse the issues of the nature of the subject and how to conduct research on it. The theoretical part provides several chapters which discuss in depth the consequences of the empirical studies for existing scholarship on legal reasoning and comparative law. This book offers a significant contribution to both the jurisprudence of legal reasoning and to the study of the role of comparative law in legal development. The analysis is sophisticated and does not exaggerate the subordinate place of comparative law in the overall scheme of legal reasoning. It merits careful study by those engaged in the practice of undertaking and using comparative law.