Cross-country comparisons of legal certainty are en vogue today. Court decisions by the Court of Justice of the European Union (‘CJEU’), as well as the European Court of Human Rights (‘ECtHR’), frequently refer to the concept of legal certainty, drawing on the experiences of Member States. The comparison of legal certainty has recently also become the subject of a research initiative, the ‘Civil Law Initiative’, which aims to show the virtues of systematically codified legal systems. Specifically, this initiative has suggested an Index of Legal Certainty, which attempts to measure how well legal systems perform under this benchmark.

The comparative law literature often claims that there is a sharp legal family divide in legal certainty. My recent paper on ‘Comparative Legal Certainty: Legal Families and Forms of Measurement’ disagrees with this view. It discusses the traditional position of a civil law advantage over the common law, as well as the challenges to this traditional position; it also provides a critical assessment of the quantitative research on questions of legal certainty.

The main finding is that general statements about a civil-common law divide in legal certainty do not hold up to scrutiny. Neither the conventional comparative analysis of this chapter, nor the quantitative research of previous studies, point towards a general advantage for either the civil law or the common law. Rather it is shown that much depends on the way legal certainty is understood. For example, the benchmark of legal certainty does not tell us whether one should have a simple codified law that even laypersons can understand, or a more elaborate law that can give a clear answer to any legal problem. The discussion of the quantitative research also shows that any assessment is sensitive to the way legal certainty is measured.

For future research, it is suggested that there is need for a new quantitative approach to measuring legal certainty. In contrast to the use of proxies in the Legal Certainty Index, this should be based on an expert assessment of the actual results of the resolution of legal problems. Considering the need for a flexible and just law, it is also important to consider that legal certainty is not an absolute aim which law makers should pursue. Notably, it is suggested that a future indicator should address both legal certainty and legal adaptability as the two corresponding aims which law makers need to balance.

Of course, this is not the only perspective that one can take on the topic of legal certainty. Thus, it is also worth mentioning that the final version of the paper is soon to be published in a book on the The Shifting Meaning of Legal Certainty in Comparative and Transnational Law (co-edited with Mark Fenwick and Stefan Wrbka). This book presents research from a range of substantive areas regarding the meaning, possibility and desirability of legal certainty in the context of a rapidly changing global society. In particular, it explores some of the tensions that now exist between the conventional expectation of legal certainty and the various challenges associated with regulating highly complex, late modern economies and societies.

Certainly, this book will also not be the final word on that matter. In order to address the variations in the meaning, possibility and desirability of legal certainty, a future research agenda could specifically explore the relationship between legal certainty and other phenomena. To some extent, this issue has always been a concern for the notion of legal certainty, as it is clear that the benefits of legal certainty need to be balanced with the benefits of flexibility of the law. Yet, as the book’s introduction explains, many more topics can also be explored with a ‘legal certainty and …’ approach, such as ‘legal certainty and legitimacy’, ‘legal certainty and development’, ‘legal certainty and social justice’, ‘legal certainty and politics’, ‘legal certainty and courts’, ‘legal certainty and legislative reform’ and ‘legal certainty and language’.

Mathias Siems is Professor of Commercial Law at Durham University.