Subtitle (titling)

In books and other works, the subtitle is an explanatory title added by the author to the title proper of a work. Another kind of subtitle, often used in the past, is the alternative title, also called alternate title, traditionally denoted and added to the title with the alternative conjunction "or" – hence its name.

As an example, Mary Shelley gave her most famous novel the title Frankenstein; or, The Modern Prometheus, where "or, The Modern Prometheus" is the alternative title. She references Prometheus, one of the Greek Titans, as a hint of the novel's themes.

A more modern usage is simply to separate the subtitle by punctuation, making the subtitle more of a continuation or sub-element of the title proper.

In library cataloging and in bibliography, the subtitle does not include an alternative title, which is defined as part of the title proper. For example, One Good Turn: A Natural History of the Screwdriver and the Screw is filed as "One Good Turn (title)" and "A Natural History of the Screwdriver and the Screw (subtitle)", while Twelfth Night, or What You Will is filed as "Twelfth Night, or What You Will (title)".