Which advice about literary genres did Horace give in Ars poetica?

In his Ars poetica, Horace provides guidance on literary composition centered on the principle of decorum, or internal propriety. He advises that each literary genre—such as tragedy, comedy, epic, lyric, satire, elegy, and epigram—must maintain its own distinct style, tone, and conventions.1

Horace emphasizes that a work must remain consistent in every aspect, requiring that the subject matter be matched with appropriate diction, metre, and form. His core advice includes:2

• Genre Integrity: A comedic theme should never be expressed using the verses of tragedy; each style must adhere to its established standards.1
• Propriety of Action: He dictates that certain events, such as violent acts, should be narrated rather than performed onstage to maintain artistic propriety.1
• Character Consistency: Characters must speak and act in a manner befitting their specific social position and rank.2

Ultimately, Horace argues that for a work of art to retain its unity, it must be consistent in every element of its execution.2