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"),