The fourth wall is a performance convention in which an invisible, imagined wall separates actors from the audience. While the audience can see through this "wall", the convention assumes, the actors act as if they cannot. From the 16th century onward, the rise of illusionism in staging practices, which culminated in the realism and naturalism of the theatre of the 19th century, led to the development of the fourth wall concept.
The metaphor suggests a relationship to the mise-en-scène behind a proscenium arch. When a scene is set indoors and three of the walls of its room are presented onstage, in what is known as a box set, the "fourth" of them would run along the line (technically called the "proscenium") dividing the room from the auditorium. The "fourth wall", though, is a theatrical convention, rather than of set design. The actors ignore the audience, focus their attentions exclusively on the dramatic world, and remain absorbed in its fiction, in a state that the theatre practitioner Konstantin Stanislavski called "public solitude" (the ability to behave as one would in private, despite, in actuality, being watched intently while so doing, or to be 'alone in public'). In this way, the fourth wall exists regardless of the presence of any actual walls in the set, or the physical arrangement of the theatre building or performance space, or the actors' distance from or proximity to the audience.
"Breaking the fourth wall" is an instance in which this performance convention, having been adopted more generally in the drama, is violated. This can be done through either directly referencing the audience, the play as a play, or the characters' fictionality. The temporary suspension of the convention in this way draws attention to its use in the rest of the performance. This act of drawing attention to a play's performance conventions is metatheatrical. A similar effect of metareference is achieved when the performance convention of avoiding direct contact with the camera, generally used by actors in a television drama or film, is temporarily suspended. The phrase "breaking the fourth wall" is used to describe such effects in those media. Breaking the fourth wall is also possible in other media, such as video games and books.
One of the earliest recorded breakings of the fourth wall in serious cinema was in Mary MacLane's revolutionary 1918 silent film Men Who Have Made Love to Me, in which the enigmatic authoress - who portrays herself - interrupts the vignettes onscreen to address the audience directly.
Oliver Hardy often broke the fourth wall in his films with Stan Laurel, when he would stare directly at the camera to seek sympathy from viewers. Groucho Marx spoke directly to the audience in Animal Crackers (1930), and Horse Feathers (1932), in the latter film advising them to "go out to the lobby" during Chico Marx's piano interlude. Comedy films by Mel Brooks, Monty Python, and Zucker, Abrahams, and Zucker frequently broke the fourth wall, such that with these films "the fourth wall is so flimsy and so frequently shattered that it might as well not exist", according to The A.V. Club.
In Akira Kurosawa's 1957 adaptation of Gorky's The Lower Depths, the film abruptly ends with Kōji Mitsui breaking the fourth wall to utter a callous remark about a fellow slum dweller's suicide. By having Mitsui use the startling technique, Kurosawa not only stresses his character's victorious nihilism but also suggests the film's theatrical origins.
Woody Allen broke the fourth wall repeatedly in his movie Annie Hall (1977), as he explained, "because I felt many of the people in the audience had the same feelings and the same problems. I wanted to talk to them directly and confront them." His 1985 film The Purple Rose of Cairo features the breaking of the fourth wall as a central plot point.
Jerry Lewis wrote in his 1971 book The Total Filmmaker, "Some film-makers believe you should never have an actor look directly into the camera. They maintain it makes the audience uneasy and interrupts the screen story. I think that is nonsense, and usually, I have my actors, in a single, look directly into the camera at least once in a film, if a point is to be served." Martin and Lewis look directly at the audience in You’re Never Too Young (1955), and Lewis and co-star Stella Stevens each look directly into the camera several times in The Nutty Professor (1963), and Lewis’ character holds a pantomime conversation with the audience in The Disorderly Orderly (1964). The final scene of The Patsy (1964) is famous for revealing to the audience the movie as a movie, and Lewis as actor/director.