Over time Nabokov's fiction becomes increasingly humorous, with more jokes used to more consequential ends. Because so marked, and so important, Nabokov's mounting use of humor invites explanation. Humor theorists, in varied words and with differing degrees of forcefulness, posit humor as offering possibilities-ontological, behavioral, circumstantial, or interpretative-unforeseen by an audience. Nabokov, experiencing reality as endlessly surprising, uses humor to endow fictive worlds with the types of surprises he most enjoys in his own world. Unlike most literary humor, Nabokov's humor emerges from a wide-ranging theory of humor, a theory that reflects Nabokov's subjectivist metaphysics. This article, as it maps relationships between Nabokov's use of humor, theory of humor, and metaphysics, sees Nabokov as pointedly using humor to alert readers to life's unpredictability.