Such sentences convey something more than a humorous impression. They surpass the usual historical records in revealing in an incisive way the social characteristics of those pioneer days. His humor is often only a means of more forcibly impressing on readers some phase of the philosophy of history. Even careless readers frequently recognize that this statement is true of much of the humor in _A Connecticut Yankee at King Arthur's Court_, which is one of his most successful exhibitions of humor based on incongruity. While his humor is sometimes mechanical, coarse, and forced, we must not forget that it also often reveals the thoughtful philosopher. To confirm this statement, one has only to glance at the humorous philosophy that constitutes _Pudd'nhead Wilson's Calendar_. Mark Twain's future place in literature will probably be due less to humor than to his ability as a philosopher and a historian. Humor will undoubtedly act on his writings as a preservative salt, but salt is valuable only to preserve substantial things. If matter of vital worth is not present in any written work, mere humor will not keep it alive. One of his most humorous scenes may be found in the chapter where Tom Sawyer succeeds in getting other boys to relieve him of the drudgery of whitewashing a fence. That episode was introduced to enable the author to make more impressive his philosophy of a certain phase of human action:-- "He had discovered a great law of human action without knowing it--namely, that in order to make a man or a boy covet a thing, it is only necessary to make the thing difficult to attain. If he had been a great and wise philosopher, like the writer of this book, he would now have comprehended that Work consists of whatever a body is obliged to do, and that Play consists of whatever a body is not obliged to do." His statement about illusions shows that his philosophy does not always have a humorous setting:-- "The illusions are the only things that are valuable, and God help the man who reaches the time when he meets only the realities." Hatred of hypocrisy is one of his emphatic characteristics. If Tom Sawyer enjoyed himself more in watching a dog play with a pinch-bug in church than in listening to a doctrinal sermon, if he had a better time playing hookey than in attending the execrably dull school, Mark Twain is eager to expose the hypocrisy of those who would misrepresent Tom's real attitude toward church and school. While Mark Twain is determined to present life faithfully as he sees it, he dislikes as much as any Puritan to see evil triumph. In his stories, wrongdoing usually digs its own grave. His strong sense of justice led him to write _Personal Recollections of Joan of Arc_ (1896), to defend the Maid of Orleans. Because he loved to protect the weak, he wrote _A Dogs Tale_ (1904). For the same reason he paid all the expenses of a negro through an eastern college.