use of words that allow alternative interpretations. In factual, explanatory prose, ambiguity is considered an error in reasoning or diction; in literary prose or poetry, it often functions to increase the richness and subtlety of language and to imbue it with a complexity that expands the literal meaning of the original statement. William Empson's (Empson, Sir William) Seven Types of Ambiguity (1930; rev. ed. 1953) remains a full and useful treatment of the subject.