Comparative Jurisprudence'Comparative Jurisprudence' started off as a complicated, ambitious and at times confusing attempt by William Ewald, in the 1990s, to rethink the foundations of comparative law (→ Legal Theory and Comparative Law). The principal ideas were presented in his monograph-length article, 'What Was It Like to Try a Rat?' (Ewald [1995a]), and in a couple of shorter pieces that explored various subsidiary aspects (Ewald [1995b]; Ewald [1998]). It is now recognized to be an analytically robust account of comparative law as an academic discipline in its own right, focused not so much on the text or even context of legal rules, as on the reasoning structures underlying them.The argument of 'Rats' is complex and occasionally hard to follow and it may clarify matters to observe that the article was the product of a long development and represents more than a single project. The initial motivation, pursued in Oxford and Göttingen in the 1980s, was entirely within the philosophy of law. Ewald was at the time on the philosophy faculty at Oxford, had studied closely the jurisprudential writings of HLA Hart and Ronald Dworkin, and was searching for a way to extend their theories. His idea was to look more closely at two interrelated matters that, in those days, were not much discussed in Oxford: first, the history of legal philosophy and, secondly, the contributions of thinkers outside the Anglophone world. There was an additional motivation. The EEC (not yet the European Union) was clearly a legal project of great significance, and he supposed it would be of philosophical interest to examine the arguments that had been made during the legal unification of Germany and Italy in the nineteenth century. One debate in particular seemed of great significance: the disagreement, at the end of the eighteenth century, between Immanuel Kant and his student Johan Gottfried Herder. Their debate was essentially over questions of nationality and morality and cultural relativism. The contemporary relevance of their debate seemed obvious.