An allegory is a work that uses symbolic characters and events to express a hidden message, generally moral, spiritual, or political. Although all allegories strongly employ symbolism, not all literature that employs symbolism qualifies as an allegory. Many stories use symbols that have a similar meaning to those in an allegory but are used for different purposes. For example, a knight might be sent on a quest to recover a sword that has been stolen from him. During his journey he encounters various obstacles that prevent him from reaching the thief immediately, but when at last he catches up with the villain he finds that he is now able to fight back. Allegorical works include novels by Charles Dickens (A Christmas Carol) and William Shakespeare (The Winter's Tale). Poems that use allegory include "The Raven" by Edgar Allan Poe and "Maniac" by Blake. Non-fiction books that use allegory include George Bernard Shaw's The Intelligent Woman's Guide to Socialism and Frederic Raphael's Zen and the Art of Motorcycle Maintenance. Allegory is used by philosophers to explain how human actions affect the world around them. In Plato's The Republic, for example, Socrates uses the story of the Allegory of the Cave to show that justice is better than injustice because it allows people to live good lives even if they lack wisdom about what justice is.