The subject of a book is what the book is about, an idea or ideas explored in the book's contents. In a nonfiction book, the subject should be fairly explicit, in the author's own words. With fiction, however, a reviewer must interpret the subject through analysis of character, setting, plot, and symbolism.
A discussion of the subject of a book might begin with its title: From where did the author derive the title? What is the title's meaning or suggestiveness? Is the title an adequate heading for the contents of the book? Or is it ambiguous or false in some way?
Other questions regarding the exploration of a book's subject by its author include: What areas of the subject are covered? (In fiction, areas of subject may be considered character concerns, setting, and plot.) What areas of the subject are left uncovered? Is this intentional, or the result of oversight or failure, on the author's part? To what degree is the author thorough or negligent in addressing the subject?
In his review of Wilderness and Razor Wire, John Calderazzo comments that writer Ken Lamberton avoids discussion of personal motivation: "Perhaps to spare his wife further humiliation and pain, Lamberton has decided not to belabor his motive for his one act of insanity. He talks vaguely of immaturity, but that's about it . . . [T]he single-mindedness of his gaze [has] implications he either doesn't recognize or won't fully discuss . . . Fixating on the near at hand may be a necessary metaphor and an undeniable fact of prison life, a way to cope with an existence that certainly scares the hell out of me. Maybe, though, Lamberton's fierce gaze derives from something he'll always carry within him: this edgy and impulsive but obviously grateful husband who knows he's not free to teach again for a living . . ."