two difficulties arise when one considers the problems of bibliographic classification systems for non-science areas:
an initial division of the world of knowledge into the three traditional academic areas of science, social science and the humanities…. The absence of an initially consistent principle of division hampers classification research for all three major discipline areas because mutual exclusivity cannot be assumed to be present at even the highest hierarchical level. Conceptual overlap between and among classes on one level inevitably influences classes lower in a hierarchy.
agreement about which academic disciplines belong to “the humanities” does not exist.