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 Dewey, or decimal, and the Cutter, or expansive.

They are outlined in the following chapters.