From The Enlightenment by Anthony Pagden, a fact which cannot be improved:
“The struggle over the identity of the Enlightenment was also a part of the Enlightenment itself. In December 1783 the Berlinische Monatsschrift, a widely read and generally progressive journal, published an article by a theologian and educational reformer named Johann Friedrich Zöllner. The article was on the desirability of purely civil marriages–a somewhat recondite topic. It might have passed unnoticed, and probably unread, if it had not been for a single footnote. “What is enlightenment?” Zöllner asked. “This question, which is almost as important as what is truth, should indeed be answered before one begins enlightening. And still I have never found it answered!”13It was perhaps the most significant footnote in the entire history of western thought–it was certainly the most widely discussed. Six years later, shortly before the outbreak of the French Revolution, the German poet and philosopher Christoph Martin Wieland–once described as the German Voltaire–while seated on the toilet and reaching for what he coyly calls a “maculature” (in other words, a piece of toilet paper), found, “not without a slight shudder of astonishment,” that the sheet of “good white soft paper” he held in his hand had printed on it six questions, the first of which was: “What is enlightenment?”14″
Planet of the Blind 