Introduction

Even in the last stronghold of domestic law – the constitutional sphere – constitutional law is increasingly comparative and transnational in scope. The theory, however, is struggling to keep pace with this aspect of contemporary practice. In no small part this is because of how the use of comparative and transnational sources points up the poverty of the traditional account of sources of law and legitimacy. The traditional account of the sources of law and legal authority is highly spatialized – essentially positivistic in nature, it imagines mutually exclusive ‘bodies’ of rules, delineated in terms of both subject-matter and jurisdiction and presided over by a conflict-like adjudicative process. According to this account, drawing sources from beyond any of the relevant borders inevitably raises questions of legitimacy. The concept of legal ideas ‘migrating’ is in this way inherently threatening to the traditional account. As long, however, as ideas from elsewhere appear in a purely persuasive guise, their invocation may have some semblance of consistency with the traditional account.

Recently, however, courts have been inclined to find that some non-binding legal sources, drawn from across traditional boundaries, may also give rise to a more demanding effect. So, legal rules that lack force or are not binding may nonetheless possess a kind of mandatory effect that cannot be explained as persuasive authority. This is apparent in many invocations of international and transnational law but it also appears elsewhere.