A new biography of Mark Twain attempts to measure the author’s importance to American literature: “His way of seeing and hearing things changed America’s way of seeing and hearing things … he was the Lincoln of American literature.’ In his prime, a century after the Declaration of Independence, Twain was a Yankee original who rendered the vocabulary and tone of the American vernacular, previously despised, in a way that was neither parody, nor caricature, but literature.”