`Suddenly it hits you: you're not twenty; you're not young any more . . . and in the meantime, while you were thinking about something else, the world has changed.'Birthday begins with a fiftieth birthday. It comes and goes without fanfare, but just a few months later, an apparently banal comment that reveals a gap in the author's knowledge of the world prompts him to sit down in a cafe and write. As he sifts through anecdotes and weaves memories together, Aira reflects on the origin of his beliefs and his incapacity to live, on literature understood from the author's and the reader's point of view, on death and the Last Judgement.