This paper first establishes a definition of ambiguity and its significance to art and to perception in general. Its understanding is framed within a hierarchical conception of musical structure most similar to that of Leonard B. Meyer (1956,1973). Following (1) an illustrative survey of occurrences of intentional ambiguity found in the standard music repertory, and (2) a discussion of the limited attention paid by music theorists to ambiguity in the past, a general theory of musical ambiguity's causes is developed. The paper's final section consists of an extensive analysis of functional ambiguity as a principal expressive vehicle in Chopin's Mazurka, Opus 17, No. 4.