Using clinical case studies and everyday examples, the author analyzes lapses such as forgetting names or foreign words, slips of the tongue, mistakes in reading and writing, bungled actions, and failures of memory and intention, arguing that these parapraxes reveal unconscious motives and repressed wishes. He demonstrates methods of free association to trace errors to underlying conflicts, contrasts apparent chance with determinism, and organizes various error types to show how ordinary faults illuminate psychic processes and the mechanisms of repression.