Diction can be defined as an author's word choice. It is "literary craftsmanship." Diction can be used in many ways—to set the mood, provide characterization, support a theme, or snag the reader's interest or his emotional response. For example, Jonathan Edwards' "Personal Narrative" is written about Edwards' relationship with God. This serious piece uses almost no figurative language; his diction is very straightforward. Edgar Allan Poe used diction to great effect in many of his short stories. In "The Tell-Tale Heart," the very first sentence not only creates the mood (of dread), but also provides characterization for the narrator (insane). It makes the reader wonder why the narrator is nervous? Is he actually insane?
TRUE!—NERVOUS—VERY, very dreadfully nervous I had been and am; but why will you say that I am mad?
Words can bring to mind associations that go beyond the denotation of the word. For instance, feeling cold from playing in the snow is very different than the chill one feels as a ghost drifts past. Diction is important not just for the reader's pleasure, but also for a writer's success. Mark Twain says it best:
The difference between the almost right word and the right word is really a large matter—’tis the difference between the lightning-bug and the lightning.