In "The Philosophy of Composition," Poe stresses the need to express a single effect when the literary work is to be read in one sitting. A poem should always be written short enough to be read in one sitting, and should, therefore, strive to achieve this single, unique effect. Consequently, Poe figured that the length of a poem should stay around one hundred lines, and "The Raven" is 108 lines.
The most important thing to consider in "Philosophy" is the fact that "The Raven," as well as many of Poe's tales, is written backwards. The effect is determined first, and the whole plot is set; then the web grows backwards from that single effect. Poe's "tales of ratiocination," e.g. the Dupin tales, are written in the same manner. "Nothing is more clear than that every plot, worth the name, must be elaborated to its denouement before anything be attempted with the pen" (Poe, 1850).
It was important to Poe to make "The Raven" "universally appreciable." It should be appreciated by the public, as well as the critics. Poe chose Beauty to be the theme of the poem, since "Beauty is the sole legitimate province of the poem" (Poe, 1850). After choosing Beauty as the province, Poe considered sadness to be the highest manifestation of beauty. "Beauty of whatever kind in its supreme development invariably excites the sensitive soul to tears. Melancholy is thus the most legitimate of all the poetical tones" (Poe, 1850).