Realism is a key issue of all textual studies (whether of literature, film, media, the past, etc.) as the more realistic a text is accepted as being the more engagement we make with it. Indeed highly realistic texts will be accepted as 'true' and in that acceptance is the power of realism as an interpellating device; i.e as a mechanism for drawing the audience to the text and getting them to adopt the ideology of the text as their own. The discourse of realism involves the different conditions that each text must meet for its audience to accept it as realistic.
TYPES OF REALISM
There are many different types of realism because each text will need a different approach to the realistic. Plots involving things that do not exist (ghosts, faster-than-light-travel, talking chickens/rats/donkeys) can still be realistic as can texts that deal in non-realistic depictions (cartoons especially) because they utilize approaches to the realistic other than an appeal to contemporary experience and photographic depiction.
1. Surface naturalism - presenting the world of the text as though it were the real world being represented (avoiding anachronisms and ensuring authenticity though appropriate locations, props, costumes, accents, etc).
2. Ecphrasis - Ecphrasis is the luxuriously detailed description of something that evokes the real through the sheer mass of descriptive effort involved. This approach to the establishment of the realistic was proposed by Barthes in his The Effect of Reality. For Barthes ecphrasis was the key to both the realistic novels of the 19th century and the bourgeois ideologies they embodied and to the disciplined realistic history that emerged alongside them.
3. Conformity to experience - if a text limits itself to the representation of that which is within the experience of its audience it will be more easily accepted as real.
4. Photography - since the invention of photography and its incredible offspring moving pictures with sound photo-realism has been the starting point for establishing the realistic.
5. Psychological or emotional realism - in this approach the audience are asked to view the characters in a text and their actions as plausible and potentially real because they seem to us to be in-line with our own emotions and psychology. This form of realism is fundamentally about the believability of character.
6. Narrative realism - form of realism in which the realistic is evoked by the telling of believable stories. If narratives are not plausible, regardless of how outlandish their content, then the text will not be accepted as realistic.
7. Content realism - this form of realism concerns the 'real' record of events and the depiction of 'real' things (such as a London street) and it is this form of realism that is most often used by news and documentary texts.
8. Genre conventions of realism - each genre has its own codes and conventions of realism and audiences will use a modality judgment (i.e. a judgment on the appropriateness of the form of realism used for the genre involved) to decide if any given text is acceptably realistic based on their prior experience of the genre and of other approaches to the realistic (e.g. non-diegetic music is typically not considered anti-realistic).
DISCOURSE OF REALISM
Discourse means both language about and/or of 'x' and communication embodying ideology and so the discourse of realism is not just the negotiation between text and audience about whether or not the text is acceptable as realistic (i.e. the result of the audience's modality judgment regarding the approaches to the realistic used in the text) but also concerns the ideological power considerations regarding realism to be found in the wider society and what interest the elite may have in the realistic. Whether or not a text is considered realistic or not will not just be the result of the creators of the text stacking up enough approaches to establishing the real and then an individual deciding if that makes the text real enough or not but also of the play of social power around the text. Sufficient backing by enough resources of social power will make a text acceptably realistic regardless of its own qualities.