Poe's literary theory repeatedly stressed art for art's sake, an idea somewhat removed from the era's general literary belief that literature should teach or preach a moral lesson. Furthermore, Poe advocated the "single effect" theory in his literary criticism and practiced it within his own poems and stories. It would be difficult to deduce any messages on Poe's part in his tales of horror and terror. He sought to frighten his readers or to intellectually entertain them, and thus introduces a full range of elements that straddled the line between science and the supernatural.