Gene Youngblood, Expanded Cinema

Pg. 64

To satisfy the profit motive the commercial entertainer must give the audience what it expects, which is conditional on what it has been getting, which is conditional on what it previously received, ad infinitum. Inherent in the term "genre," which applies to all entertainment, is that it must be probable. The content of westerns, gangster movies, romances, etc., is probable in that it can be identified and comprehended simply by classification.