While anthropologists for a long time now have analysed the rules of marriage in many non-Western societies, medieval incest prohibitions have been studied less frequently. Sam Worby, in her 2010 study, now available in a paperback edition, takes a fresh view on law and kinship by studying both canon law and common law – and hence the rather different definitions of kinship in the two jurisdictions. The first two chapters deal with kinship structures in both laws. Canon law dealt with kinship mainly in the context of marriage, and prohibited marriages on ground of consanguinity even between very distant cousins. In addition, canon law tended to assimilate consanguinity, affinity and spiritual kinship (resulting from sponsorship at baptism). At common law, kinship was mainly important as it determined inheritance of real property. Crucially, these rules differed from canon law; terms like ‘cousin’ meant different things in both laws. As Worby explains in her third chapter, canonists, common lawyers and other scholars were very well aware of the differences between the laws. She also makes a clear case that canon law definitions of kinship had a significant impact on common law discussion of kinship (and likewise on theology and Roman law) but not the other way round. Common lawyers who laid down the rules of inheritance in their tracts time and again drew on canon law. Very usefully, Worby edits some of these tracts in her appendices.

Chapter iv deals with ‘Kinship laws in practice’. Unsurprisingly perhaps, Worby finds that the rules of canon law were not applied strictly, but used in various ways, and sometimes the best evidence of lay knowledge of the law comes from cunning ways to abuse it. While ecclesiastical courts relatively rarely had to deal with kinship, common law cases of this kind are very common. The law on cosinage was unclear, and this may also explain why common lawyers drew on canon law concepts. The fifth chapter more generally discusses how both laws influenced kinship. Both laws may have contributed to the decline of ‘clans’ which (as Worby is quick to admit) played no important role in thirteenth-century England but may have done so before 1066. In any case, canon law kinship according to Worby's findings had a considerable influence on the way people thought about family relations in late medieval England. However, she also makes clear that canon law concepts of affinity were met with a certain scepticism. Unfortunately, spiritual kinship is not discussed in this chapter, although it would have made a very good test case for the influence of canon law kinship. Rather than stressing the similarities of modern and medieval family structures in England, as MacFarlane had done, Worby makes a good case that late medieval kinship – in England as well as in the rest of Latin Christianity – was influenced by canon law.