Catherine Valcke's new book, Comparing Law: Comparative Law as Reconstruction of Collective Commitments, radically raises the stakes in the debate about the nature and methods of comparative law. Valcke's aim is nothing less than to reconstruct the theoretical and methodological framework of comparative law in order to secure its place as an autonomous discipline. Interestingly, and perhaps ironically, this project takes Valcke away from the insular field of comparative law to the wider world of systems theory and liberal political and legal thought.

As the subtitle of this theoretically rich book suggests, Valcke characterizes law as ‘collective commitment’, where law is ‘an argumentative social practice that both reflects and constitutes a community's commitment to governing itself in accordance with certain ideals’ (p 18). Seeing law as collective commitment seeks to strike a balance between too ‘thin’ (or over-inclusive) and too ‘thick’ (or under-inclusive) definitions of law (pp 18–19). Valcke identifies six essential features (or normative ideals) in law as collective commitment: effectiveness, argumentativeness, coherence, publicness, formality, and normativity. She then discusses these features mainly through liberal political and legal philosophy. For instance, she describes the ideal of effectiveness with reference to Ronald Dworkin's views about government officials’ commitment to legal rights and duties (p 22). Similarly, Valcke bases the ideal of argumentativeness on the Kantian notion of self-governance and the ideal that coercive laws have to be based on free choice (pp 23–24). The Kantian notion of self-governance also motivates the ‘coherence imperative’, or the argument that law ought to be governed ‘by the same imperatives as govern reason itself’ (pp 27–28). Likewise, Valcke defines the publicness of law as the Rawlsian ideal that valid legal arguments must be transparent and open to public scrutiny (p 31). Formality refers to the definition of law in terms of its institutional pedigree rather than its substance (pp 35–36). Normativity, finally, signifies the aspirational nature of law (p 39).

The notion of law as collective commitment opposes both the natural law tendency to ignore the differences between national legal systems and the legal positivist tendency to deny the connectedness of national legal systems. Drawing on Niklas Luhmann's systems theory, Valcke contends that legal systems establish their collective commitments in an autopoietic or self-delineating manner (p 87). The consequence of such autopoiesis, in Valcke's view, is that ‘all the various rules, arguments, source materials and so on that make up legal systems are more or less directly aimed at the single binary question of what will or will not end up being implemented by the courts’ (p 147). Valcke softens the impact of this statement by comparing legal systems to bee swarms, which have well-defined institutional centres and fluid edges (p 144). Valcke argues that in trying to understand foreign law, comparatists take part in the same self-referential legal games as local actors. At the same time, they bring to the game unique viewpoints, such as an outsider's attentiveness to various background rules (pp 124–27).

Despite breaking novel theoretical ground in comparative law, the aim of this carefully argued book is not to revolutionize comparative law scholarship. Instead, Valcke defends many research practices in mainstream comparative law. For instance, Valcke concludes that the focus of comparative lawyers on state-based national legal systems is ‘fully defensible’ given the self-delineating nature of these legal systems (p 221). She also defends the search for external criteria, or tertium comparationis, for macro-level comparisons between national legal systems (p 213). She compares macro-level legal comparison to an attempt to find a ‘best dog’ in a dog show where the contestants are of different breeds (p 214). Valcke argues that proportional comparisons of dogs against their relative goodness within their particular breeds are possible in this context (p 214). In Valcke's view, ‘“[d]og-ness” … provides a perfectly valid tertium comparationis for comparing fox terriers and poodles despite there being no single dog-ness metric running across them both’ (p 214). Analogically, Valcke argues that different legal systems can be compared against the core conceptions of law described above, such as the ideal of coherence (pp 214–15).

Although Valcke aspires to understand legal systems on their own self-referential terms (pp 1, 219), she also insists on ‘firm if minimal a priori limits on what can qualify as a legal system’ (pp 15–16). Comparatists whose theoretical and ideological sensibilities fall in line with the liberal foundations of these ‘a priori limits’ will find this book an eminently plausible basis for conducting legal comparisons. Scholars who are situated outside the collective commitments of liberal political and legal thought may approach the book more selectively. On the one hand, these scholars will find Valcke's book insightful in a number of ways. For instance, the idea of law as collective commitment is meant to take into account various degrees of commitment to the six features or ideals of law (p 40). Valcke argues that these ideals exist in ‘even the most tyrannical’ regimes (pp 41–43). This observation is helpful for acknowledging some of the various paradoxical impulses that make up illiberal political and legal systems. Similarly, the view of law as a self-referential system can coexist with the illiberal notion of the primacy of the political sphere. Illiberal political leaders sometimes insist that law is and should be autonomous – while at the same time establishing means to suspend the autonomy of the law when political necessities so require. On the other hand, Valcke's definition of law originates in a political ideology which illiberal (and anti-liberal) regimes and jurists explicitly oppose. In a moment of honest self-reflection, loyalist jurists in a self-defined proletariat's dictatorship would probably be ambivalent about all of the six ideals of law as collective commitment, including the ideals of formality and coherence. It is not obvious whether the book's definition of law helps the reader to understand illiberal legal systems on their own terms, except perhaps as a point of contrast.

Of course, it may well be that the primary audience of this book are neither the students of illiberal legal regimes nor the critics of liberal political and legal thought. Although Valcke seeks to facilitate the largest possible range of meaningful comparisons between different legal systems (stating, among other things, that even Nazi law might be considered ‘law’), she is also committed to ‘weeding out non-legal comparisons’ from the field of comparative law (pp 68–70). At the same time, the book demonstrates the benefits of using non-legal intellectual resources for comparative law research. Valcke's expert use of philosophical sources also exemplifies the need for comparative lawyers to venture beyond the self-referential debates of their discipline. A latent lesson of the book is that theoretical and pragmatic comparative projects are based on various ideological background assumptions which can be examined critically. There is no better place to start this critical examination than this book.