This was Twain's most serious, philosophical and above all, private book. He kept it locked in his desk, considered it to be his Bible, and spoke of it as such to friends when he read them passages. He had written it, rewritten it, was finally satisfied with it, but still chose not to release it until after his death. The book appears in the form of a dialogue between an old man and a young man who discuss who and what mankind really is. The arguments presented can change the reader's entire outlook on life because it provides a completely new and different way of looking at who we are and the way we live. Anyone who thinks Twain was not a brilliant philosopher should read this book. We all like to see ourselves as completely free and autonomous individuals, yet this book puts forth the ideas that 1) We are nothing more than machines and originate nothing - not even a single thought; 2) All conduct arises from one motive - self-satisfaction; 3) Our temperament is completely permanent and unchangeable; and 4) Man is of course a product of heredity and the future, being fixed, is irrevocable -- which makes life completely pre-determined. If these points are true, then buying and reading this book is not in your control, but simply must be done because it was meant to be. If these points are not true you might still wish to make an independent decision to enjoy a thought-provoking book by a great and legendary writer.