Poetry is a form of literary art which uses aesthetic and rhythmic qualities of language to evoke meanings in addition to, or in place of, prosaic ostensible meaning. Poetry has traditionally been distinguished from prose by its being set in verse;[a] prose is cast in sentences, poetry in lines; the syntax of prose is dictated by meaning, whereas that of poetry is held across metre or the visual aspects of the poem. Prior to the nineteenth century, poetry was commonly understood to be something set in metrical lines; accordingly, in 1658 a definition of poetry is "any kind of subject consisting of Rythm or Verses". Possibly as a result of Aristotle's influence (his Poetics), "poetry" before the nineteenth century was usually less a technical designation for verse than a normative category of fictive or rhetorical art. As a form it may pre-date literacy, with the earliest works being composed within and sustained by an oral tradition; hence it constitutes the earliest example of literature.
Prior to the eighteenth century, poetry was commonly understood to be what?