Edgar Allan Poe's Short Story Dictum

The novel differs from the short story in more than just length, but they both share the dynamic quality of character-moved-by-plot. But the difference is, that on the long trip the novel provides, there is space and time for a quantity of incidents and effects. Edgar Allan Poe spoke of the short story as providing "a single and unique effect" toward which every word contributes: "If the author's initial sentence tends not to the bring out this effect, then he has failed in his first step. In the whole composition there should be no word written, of which the tendency, direct or indirect, is not to the one pre-establishsed design." Poe's famous "unique effect" dictum can of course be taken too strictly, but it does seem to be the case that there is a degree of unity in a well-wrought short story--what we call an "harmonious relationship of all its aspects"--that isn't necessarily found in a good novel, that isn't perhaps even desirable in a novel.

Rust Hills, Writing in General and The Short Story in Particular, 1987