Ian McEwan’s Saturday explores the tension between fundamental human polarities, polarities the novel shares with many improvisations (texts that claim unmediated, spontaneous, careless, or inspired creation): immediacy vs. mediation; freedom vs. necessity; spontaneity vs. care and craft; Hermes vs. Saturn; right- vs. left-brain. McEwan’s protagonist is both improviser and, as neurosurgeon, careful craftsman. His day provides him opportunities to confront and resolve these dualities. The novel exhibits improvisation’s formal conventions and thematic features, demonstrating their synergy. Seen through the lens of improvisation, the novel dramatizes the right-brain’s pushback in the life of a man almost wholly dedicated to the rationalistic, analytic left-brain.