Hellenistic and Latin rhetors divided style into: the grand style, the middle style and the low (or plain) style; certain types of vocabulary and diction were considered appropriate for each stylistic level. A discussion of this division of styles was set out in the pseudo-Ciceronian Rhetorica ad Herennium. Modeled on Virgil's three-part literary career (Aeneid, Bucolics, Georgics), ancient, medieval and Renaissance theorists often linked each style to a specific genre: epic (high style), didactic (middle style) and pastoral (plain style). In the Middle Ages, this concept was called "Virgil's wheel". For stylistic purists, the mixing of styles within a work was considered inappropriate, and a consistent use of the high style was mandated for the epic. However, stylistic diversity had been a hallmark of classical epic (as seen in the inclusion of comic and/or erotic scenes in the epics of Virgil or Homer).
The principle of decorum was an influential concept even in the looser rescripts of Romanticism. Poetry, perhaps more than any other literary form, usually expressed words or phrases that were not current in ordinary conversation, characterized as poetic diction.
Concepts of decorum, increasingly sensed as inhibitive and stultifying, were aggressively attacked and deconstructed by writers of the Modernist movement, with the result that readers' expectations were no longer based on decorum, and in consequence the violations of decorum that underlie the wit of mock-heroic, of literary burlesque, and even a sense of bathos, were dulled in the twentieth-century reader.
In Renaissance Italy, important debates on decorum in theater were set off by Sperone Speroni's play Canace (portraying incest between a brother and sister) and Giovanni Battista Giraldi's play Orbecche (involving patricide and cruel scenes of vengeance). In seventeenth-century France, the notion of decorum (les bienséances) was a key component of French classicism in both theater and the novel (see French literature of the 17th century).
The precepts of social decorum as we understand them, of the preservation of external decency, were consciously set by Lord Chesterfield, who was looking for a translation of les moeurs: "Manners are too little, morals are too much. The word decorum survives in Chesterfield's severely reduced form as an element of etiquette: the prescribed limits of appropriate social behavior within a set situation. The use of this word in this sense is of the sixteenth-century, prescribing the boundaries established in drama and literature, used by Roger Ascham, The Scholemaster (1570) and echoed in Malvolio's tirade in Twelfth Night, "My masters, are you mad, or what are you? Have you no wit, manners nor honesty, but to gabble like tinkers at this time of night?...Is there no respect of persons, place nor time in you?
The place of decorum in the courtroom, of the type of argument that is within bounds, remains pertinent: the decorum of argument was a constant topic during the O.J. Simpson trial, to pick an egregious example that remains in the public consciousness.