Sigmund Freud, an Austrian neurologist and one of the most influential thinkers of the 1900s, spent much of his life devoting himself to psychoanalysis, a technique used to treat psychopathology through dialogue. He devoted himself to studying the human brain, and in the short essay The Uncanny, he focuses his writing on ideas that would generally make many people uncomfortable.
For Freud, to call something "uncanny" (in German, "unheimlich") is to describe a relationship where one is both familiar and unfamiliar with an object. He delves into the etymology of the German term for familiar (unheimlich), showing how it can mean both familiar or comfortable, but can also be used to mean its supposed opposite—the unheimlich or uncanny, that which is unfamiliar or mysterious. The uncanny, then, is something that one does recognize, but in a strange or unexpected way. It is this tension between the familiar and the unfamiliar, the heimlich and unheimlich, that defines the uncanny, according to Freud. Freud shows how much of what we find "uncanny" is actually the return of a memory or experience from infancy, and even from earlier phases of humanity, that we have repressed, and that now confronts us once again.
The essay remains one of Freud's most widely read works. Its lasting influence has been to establish the theories and procedures of psychoanalysis in the humanities, especially in the study of literature, where Freud's ideas still remain largely unchallenged. Freud's reading of the "The Sand-Man," the story by ETA Hoffmann that he analyzes in the essay's second section, is widely considered inescapable, if not definitive. The Uncanny is also considered one of the founding texts of artistic modernism, highlighting the artistic effects like the ugly, the disturbing, and the disquieting. The effects of the essay can perhaps be most clearly seen in the paintings of the Surrealist movement, which sought to defamiliarize everyday objects (like Magritte's green apple) and make them "uncanny."