The Roman poet Horace, in his poetic treatise called the Ars Poetica (“The Art of Poetry”), is often associated with an approach to writing that emphasizes the need to appeal to and satisfy an audience. One way to please an audience is to observe what is sometimes called “decorum” – that is, to depict persons and things in ways that seem appropriate to their natures or appropriate in terms of custom.
One passage of the Ars Poetica in which the ideal of decorum plays an especially important part is the passage in which Horace discusses how to depict persons onstage in appropriate or decorous ways. Thus (in the translation by A. S. Kline), Horace advises aspiring poets or dramatists that they should
note the behaviour of every age-group,
Give grace to the variation in character and years.
For example, boys should be depicted as most boys commonly behave; teenagers should be depicted in ways that seem appropriate to teenagers; and so on in the cases of young men, mature men, and old men. To depict an old man behaving like a young boy would be inappropriate and would be hard for any audience to accept. It would be a violation of decorum and would seem quite literally incredible even risible. Or, as Horace himself puts it,
So lest we chance
To assign youth’s part to age, or a boy’s to a man,
Always adopt what suits and belongs to a given age.
Horace borrows this idea (as he borrows much else) from The Poetics of Aristotle. Aristotle had been very concerned that every part of a work of art should have a necessary and inevitable connection to every other part. In other words, Aristotle had valued complex unity. Horace’s demands are for a simpler kind of unity, and he places a great deal of emphasis on doing what is customary. Custom is merely the record of what many previous audiences have been willing to accept. For Horace, decorum is closely connected with custom. Horace is mainly concerned with helping aspiring poets to avoid making fools of themselves and being laughed at for (among other things) violating decorum. As he puts it in the famous opening lines of the treatise (which is itself a poem),
If a painter had chosen to set a human head
On a horse’s neck, covered a melding of limbs,
Everywhere, with multi-coloured plumage, so
That what was a lovely woman, at the top,
Ended repulsively in the tail of a black fish:
Asked to a viewing, could you stifle laughter, my friends?
To paint a horse with a human head, or a woman with the tail of a fish, would be to violate decorum. Audiences, when faced with such violations, cannot “stifle laughter.” If a poet wants to avoid making himself seem ridiculous, he had better observe decorum. This, in any case, is one of the key ideas of the Ars Poetica.
Something extra: The literary theorist M. H. Abrams, in his important book titled The Mirror and the Lamp, argues that any literary theory that tries to be complete will have to account for four major aspects of literature: the writer, the text, the audience, and "reality." Abrams further argues that each theory will tend to emphasize one of these aspects as most important, and that this emphasis will color that theory's approach to all three of the other aspects. For Horace, the aspect of literature most emphasized is the audience. Horace is very concerned to make sure that any work of literature is found acceptable by the audience. This is his chief concern.