In conjunction with the unity of effect, we have Poe's dictum on the appropriate length of a work of art. Poe holds that "a long poem does not exist . . . that the phrase 'a long poem' is a flat contradiction in terms." Therefore, a work of art should be able to achieve its effect in one sitting. For this reason, Poe believed that the greatest art was contained in a poem of about 100 lines (his most famous poem, "The Raven," is 108 lines long), and Poe, in a similar vein, believed that the short story should be of a length that one could read it in one sitting. The totality of effect, he said, was destroyed if two sittings were required for a work of art.
Such long poems as Paradise Lost were, for Poe, a series of poems. If the purpose of art — a poem, or a short story — is to excite and elevate the soul, then "after the lapse of half an hour," the mind cannot sustain such pure emotion. Consequently, Poe's theory about the length of the work of art — "to be read in one sitting" and no more than "half an hour" — has influenced many subsequent writers.
In terms of Poe's actual practice of writing literature, the reader or critic can deduce certain principles that Poe himself never set down, but that he practiced again and again as an author. For example, Poe is considered to be the father of the modern detective story. Concerning this, certain critical principles associated with the writing of the detective story are presented in the introduction to and discussions of "The Murders in the Rue Morgue" and "The Purloined Letter," yet Poe himself never wrote down a unified critical principle which should govern the writing of a detective story. One can see, however, that the literary principles that Poe employed in writing his own detective stories, in large part, are universal principles that apply to a major portion of all detective fiction being written today.
