The meanings of these terms have more depth when their Anglo-Saxon origins are considered. The concept of bookland arose in the seventh century and referred to land that could be 'alienated' (i.e., disposed of) at will. It evolved to resemble ownership in the modern sense. Folkland was land held under ancient, unwritten folk-law or custom and by that custom it could not be alienated (i.e., removed) from the kin of the holder, except under special circumstances. No such claim by the kin could be made on bookland. The definition of those ancient folk-laws and customs, and the definition of the word "folkland", has long been the subject of controversy. The model suggested by the historian Patrick Wormald, given in the definition above, allows for the graceful sidestepping of that controversy.