Final answer:
Edgar Allan Poe's single effect theory dictates that all elements of a short story should contribute to one emotional effect, as seen in his work "The Fall of the House of Usher."
Step-by-step explanation:
Edgar Allan Poe's single effect theory refers to his belief that a short story should be constructed to achieve a single, emotional effect in the reader. According to Poe, every element of the story, including character, setting, and detail, should contribute to this effect. In "The Fall of the House of Usher," for example, Poe meticulously crafts the atmosphere, characters' psychological states, and events to evoke a sense of doom and gloom, in alignment with this principle. Poe's approach to storytelling has influenced the craft of writing significantly, stressing the importance of deliberate artistic choice and unity of effect.