Classifying Books
Classifying books is Adler's first rule of analytical reading: know what kind of book you are reading, and know it as early as possible.
This is not library science for its own sake. Classification changes the reading method. A practical book asks what you should do. A theoretical book asks what is the case. Imaginative literature works through experience, image, and form rather than through explicit propositions and arguments. If you misclassify the book, you will ask the wrong questions of it.
The underlying principle is simple: method follows object. You do not read a novel as if it were a treatise, or a political tract as if it were pure description. This makes classifying books a special case of problem framing: before solving the reading problem, define what sort of thing is in front of you.