hemiola
A rhythmic device that creates the effect of shifting between duple and triple meter, typically by grouping six beats as either three groups of two or two groups of three.
In Depth
Hemiola (from the Greek hemiolia, meaning "one and a half") occurs when a passage in triple meter is temporarily reorganized to sound like duple meter, or vice versa. The most common form appears in 3/4 time: instead of three groups of two eighth notes per measure (1-2, 1-2, 1-2), two measures are regrouped into two groups of three eighth notes (1-2-3, 1-2-3), creating a momentary sense of 3/2 time within 3/4 time.
The device was a favorite of Baroque composers, particularly Handel, who used hemiolas so frequently at cadential points that they became a stylistic hallmark. In Romantic music, Brahms employed hemiolas pervasively, layering multiple metric conflicts to create a uniquely ambiguous rhythmic surface. The technique is fundamental to West African and Latin American music — the tension between three and two is the driving force behind son clave, rumba, and countless other rhythmic patterns. Leonard Bernstein's "America" from West Side Story features one of the most famous hemiolas in popular music.
Bernstein's "America" from West Side Story constantly shifts between 6/8 and 3/4 — the dancers' lyrics "I like to be in A-mer-i-ca" alternate between the two meters, making the hemiola both heard and felt physically.