Brian Campbell Vickery quotes
The most important characteristic of documentary classification is that it is concerned with subjects, not just entities of taxonomic classification. What is the nature of the specific subjects - the themes on which books, parts of books, articles or parts of articles are written? A study of book titles alone would suggest that literary subjects have simple names like 'War, Religion', 'Boats', 'Musica; pitch', 'Colour', 'Acridines', 'Wild flowers', and so on. But the study of articles on the documentation level reveals that such titles are simple in appearance only. Such a literary subject is in reality a complex aggregate of specific subjects, eahc which is the main theme discussed from one particular aspect.
Brian Campbell Vickery