David Bordwell offers a useful inventory of categories used in film criticism, many of which have been accorded the status of genres by various commentators:
Grouping by period or country (American films of the 1930s), by director or star or producer or writer or studio, by technical process (CinemaScope films), by cycle (the 'fallen women' films), by series (the 007 movies), by style (German Expressionism), by structure (narrative), by ideology (Reaganite cinema), by venue ('drive-in movies'), by purpose (home movies), by audience ('teenpix'), by subject or theme (family film, paranoid-politics movies). (Bordwell 1989, 148)
Another film theorist, Robert Stam, also refers to common ways of categorising films:
While some genres are based on story content (the war film), other are borrowed from literature (comedy, melodrama) or from other media (the musical). Some are performer-based (the Astaire-Rogers films) or budget-based (blockbusters), while others are based on artistic status (the art film), racial identity (Black cinema), locat[ion] (the Western) or sexual orientation (Queer cinema). (Stam 2000, 14).
Bordwell concludes that 'one could... argue that no set of necessary and sufficient conditions can mark off genres from other sorts of groupings in ways that all experts or ordinary film-goers would find acceptable' (Bordwell 1989, 147).
Robert Stam argues that 'subject matter is the weakest criterion for generic grouping because it fails to take into account how the subject is treated' (Stam 2000, 14).
Christine Gledhill: 'Genres... are not discrete systems, consisting of a fixed number of listable items'
It is easy to underplay the differences within a genre. Steve Neale declares that 'genres are instances of repetition and difference' (Neale 1980, 48). He adds that 'difference is absolutely essential to the economy of genre' (ibid., 50): mere repetition would not attract an audience.
John Hartley notes that 'the same text can belong to different genres in different countries or times'
David Buckingham argues that 'genre is not... simply "given" by the culture: rather, it is in a constant process of negotiation and change' (Buckingham 1993, 137)
Nicholas Abercrombie suggests that 'the boundaries between genres are shifting and becoming more permeable' (Abercrombie 1996, 45);
Susan Hayward argues that genre conventions change 'according to the ideological climate of the time'
Nicholas Abercrombie, 'genres permit the creation and maintenance of a loyal audience which becomes used to seeing programmes within a genre'
Christine Gledhill: 'differences between genres meant…