"What Is Man?" by Mark Twain is a thought-provoking and philosophical work that delves into the complexities of human nature, the nature of existence, and the eternal question of what it truly means to be human. Through a series of conversations between an old man and a young man, Twain explores the fundamental themes of free will, determinism, morality, and the meaning of life. The book opens with the young man expressing his skepticism about the concept of free will, arguing that human actions are merely a product of external influences and circumstances. In response, the old man engages in a dialogue that challenges the young man's perspective and delves into the intricacies of human psychology and behavior.