What they share is the intent to manipulate the viewers's emotions, often by playing with the amount of information a viewer knows relative to what characters know. Seven and Silence of the Lambs are very different from say, Seven Vertigo Vertigo or Shadow of a Doubt. In contrast, westerns are largely defined by their shared setting, timeframe and standardized iconography. They ostensibly take a place in a specific geographical and historical context, and employ artifacts and events drawn from this context in their mise en scene and narrative structure. We are very aware of instances when the filmmaker manipulates these conventions, whether it be Mel Brooks in or Walter Hill in Last Man Standing .
Musicals are another genre defined by common formal and narrative elements.
Films such as Meet Me in St Louis or Pocahontas both, in very different ways, integrate narrative and musical numbers to work through a standardized story about love and romance. For most of the classic studio era, the vast majority of films made in Hollywood fit easily into a specific genre. Audience foreknowledge prescribed how viewers interpreted films. Some genres have since waned in popularity. In the early fifties for example, forty percent of Hollywood's annual output were westerns - a figure which is hard for us to believe today.