The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
Convention: A literary device, form, style, situation, or usage so widely employed that, however unrealistic, it has become accepted and even expected by knowledgeable readers or audiences. Conventions create a framework within which an author operates, entailing both restrictions and a certain freedom; the conventions of science fiction, for instance, vary from those of the romance, and within the latter genre, the conventions of a bodice-ripping Harlequin romance differ from other subtypes, such as medieval romances. Some conventions gain acceptance because they facilitate the presentation of material or enhance the quality of the aesthetic experience. For instance, onstage in a play a single set of large papier-mâché cylinders can represent tree trunks in one scene and architectural columns in the next, and flashbacks may interrupt the present action of a narrative to depict an earlier event. Sometimes an original story (the medieval damsel in distress), character type (the mustachioed villain of Victorian melodrama), or theme (the romantic idea that we should “get back to Nature”) will so speak to the fears, fantasies, or preoccupations of an age that it will be repeated in a variety of different works, remaining conventional as long as new writers rework it and new audiences accept it.
In the twentieth century, convention took on an even broader meaning, thanks in part to structuralist critics who considered every literary work to include a plethora of codes. The reader or viewer, structuralists argued, “naturalizes” these codes by squaring them with his or her culturally determined assumptions and perceptions.
EXAMPLES: William Shakespeare’s frequent use of asides, soliloquies, and stock characters (such as the fool) are conventions. Equally conventional, in Shakespeare’s day, was the practice of using male actors for all the women’s parts (and, therefore, the parts of women pretending to be men, like Viola in Twelfth Night  and Rosalind in As You Like It [c. 1600]). In our own day, it is conventional for women to play women’s roles in plays — including plays by Shakespeare. Nonetheless, our appreciation of a play like Twelfth Night or As You Like It still depends upon conventions. Audiences accept that the heroines of these two plays are mistaken for the men they pretend to be, even though the parts are played by women who look like women, masculine garb and hairstyle notwithstanding.
In Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation (2003), Lynne Truss argues that punctuation is not “just a set of conventions,” but a useful, even critical one — for to say someone “eats shoots and leaves” is far different than to say he or she “eats, shoots, and leaves.”