consider the library's field and its possibilities of growth, and
let the first work on the books be such as will never need to be done
over.

To classify books is to place them in groups, each group including,
as nearly as may be, all the books treating of a given subject, for
instance, geology; or all the books, on whatever subject, cast in a
particular form--for instance, poetry; or all the books having to do
with a particular period of time--for instance, the middle ages. Few
books are devoted exclusively to one subject and belong absolutely
in any one class. The classification of books must be a continual
compromise. Its purpose is not accurately to classify all printed
things, this can't be done; but simply to make certain sources of
information--books--more available. Any classification, if it gets the
books on a given subject side by side, and those on allied subjects
near one another, is a good one.

Books may be classified into groups in a catalog or list, yet
themselves stand without order on the shelves. For convenience in
getting for anyone all the books on a given subject, and especially
for the help of those who are permitted to visit the shelves, all
books should stand in their appropriate classes. Each book, therefore,
should bear a mark which will tell in what class it belongs;
distinguish it from all other books in that class; show where it
stands on the shelves among its fellows of the same class; and
indicate which one it is of several possible copies of the same book.
This mark can be used to designate the book in all records of it,
instead of the larger entry of its author and title.

There are two classification systems worthy of consideration, the