A non-satirical work by Twain in the form of Socratic-like dialogue between an Old Man arguing that man is merely a machine with no free will or self-sacrifice (a determinist) and a Young Man who is hesitant to believe him without requiring much elaboration first.
This has been on my mental to-read list for quite some time; nearly a year now. I read snippets of it when I had first began learning about Determinism here and there. Reading it now I can't say it really told me anything I didn't know, even for its time the work wasn't necessarily groundbreaking, but it is written in such a way that is enjoyable to read and very fascinating nonetheless.
It's simultaneously thorough and flawed. Some major arguments where excluded, of which Twain probably was just unaware of. But the book kind of urges you to make the arguments yourself; to take what the book says and apply it to real-life situations. It still would have been nice to see the Young Man have a bit better argumentation.
The book, especially towards the end, uses the word "God" a lot, but it's not really in the religious sense of the word (Twain was far from a religious man). The word "God" here is really only used as a placeholder word that is easily interchangeable with Evolution, Chance, Extraterrestrials, Flying Spaghetti Monster, or really anything you choose.
I can't really say much more other than to read it. It's a great piece on Free Will, Determinism, and Self-Sacrifice. It's enjoyable and accessible, introductory even.