Thegreatestmoderncriticshavelaiditdownasarulethatanheroicpoemshouldbefoundeduponsomeimportantpreceptofmoralityadaptedtotheconstitutionofthecountryinwhichthepoetwrites。HomerandVirgilhaveformedtheirplansinthisview。
AsGreecewasacollectionofmanygovernments，whosufferedverymuchamongthemselves，andgavethePersianemperor，whowastheircommonenemy，manyadvantagesoverthembytheirmutualjealousiesandanimosities，Homer，inordertoestablishamongthemanunionwhichwassonecessaryfortheirsafety，groundshispoemuponthediscordsoftheseveralGrecianprinceswhowereengagedinaconfederacyagainstanAsiaticprince，andtheseveraladvantageswhichtheenemygainedbysuchdiscords。Atthetimethepoemwearenowtreatingofwaswritten，thedissensionsofthebarons，whowerethensomanypettyprinces，ranveryhigh，whethertheyquarrelledamongthemselvesorwiththeirneighbours，andproducedunspeakablecalamitiestothecountry。Thepoet，todetermenfromsuchunnaturalcontentions，describesabloodybattleanddreadfulsceneofdeath，occasionedbythemutualfeudswhichreignedinthefamiliesofanEnglishandScotchnobleman。Thathedesignedthisfortheinstructionofhispoemwemaylearnfromhisfourlastlines，inwhich，aftertheexampleofthemoderntragedians，hedrawsfromitapreceptforthebenefitofhisreaders：
Godsavetheking，andblessthelandInplenty，joy，andpeace;
Andgranthenceforththatfouldebate’Twixtnoblemenmaycease。
Thenextpointobservedbythegreatestheroicpoetshathbeentocelebratepersonsandactionswhichdohonourtotheircountry：