Those who have read "Roughing It" or "Life on the Mississippi" or "Pudd'nhead Wilson" will have seen Mark Twain's flair for technical descriptions and definitions. You know that he liked nothing better than turning a challenging process or device or term into a clear picture for the reader. His descriptions of a quartz mill, of assaying, and of pocket mining in "Roughing It" are models of fine technical style, as are his descriptions of sounding in "Life on the Mississippi" and fingerprinting in "Pudd'nhead Wilson". His definition of "lagniappe" is a classic. But Mark Twain was more than a practitioner of technical writing: he was also a theorist about the qualities of the writing craft. His novels, letters, essays, and miscellaneous prose are sprinkled with comments on writing, comments that can be made to read like a set of rules. And that is what the author does in this article: he turns these scattered comments into a list.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>