There is first the literature of knowledge, and secondly, the 
literature of power.  The function of the first is--to teach; the 
function of the second is--to move, the first is a rudder, the 
second an oar or a sail.  The first speaks to the mere discursive 
understanding; the second speaks ultimately, it may happen, to 
the higher understanding or reason, but always through affections 
of pleasure and sympathy.
      - Thomas De Quincey ("The Opium Eater"),
 — Thomas De Quincey ("The Opium Eater")
  Literature