Enquiry Concerning Human Understanding - pg. 106

To return to the comparison of history and epic poetry, we may conclude, from the foregoing reasonings, that, as a certain unity is requisite in all productions, it cannot be wanting in history more than in any other; that, in history, the connexion among the several events, which unites them into one body, is the relation of cause and effect, the same which takes place in epic poetry and that, in the latter composition, this connexion is only requied to be closer and more sensible, on account of the lively imagination and strong passions, which must be touched by the poet in his narration. The PELOPONNESIAN war is a proper subject for history, the siege of ATHENS for an epic poem, and the death of ALICIBADES for a tragedy.