<P> In line 191, Horace warns against deus ex machina, the practice of resolving a convoluted plot by having an Olympian god appear and set things right . Horace writes "Nec deus intersit, nisi dignus vindice nodus": "That a god not intervene, unless a knot show up that be worthy of such an untangler". </P> <P> Perhaps it can even be said that the quotability of Horace's Ars Poetica is what has given it a distinguished place in literary criticism: The Norton Anthology of Theory and Criticism says: </P> <Dl> <Dd> <Dl> <Dd> It would be impossible to overestimate the importance of Horace's Ars Poetica (Art of Poetry) for the subsequent history of literary criticism . Since its composition in the first century BCE, this epigrammatic and sometimes enigmatic critical poem has exerted an almost continual influence over poets and literary critics alike - perhaps because its dicta, phrased in verse form, are so eminently quotable . Horace's injunction that poetry should both "instruct and delight" has been repeated so often that it has come to be known as the Horatian platitude . </Dd> </Dl> </Dd> </Dl> <Dd> <Dl> <Dd> It would be impossible to overestimate the importance of Horace's Ars Poetica (Art of Poetry) for the subsequent history of literary criticism . Since its composition in the first century BCE, this epigrammatic and sometimes enigmatic critical poem has exerted an almost continual influence over poets and literary critics alike - perhaps because its dicta, phrased in verse form, are so eminently quotable . Horace's injunction that poetry should both "instruct and delight" has been repeated so often that it has come to be known as the Horatian platitude . </Dd> </Dl> </Dd>

Where does the advice that a playwright should attempt to please and instruct come from