From the 17th century onward, trio has been used to describe a contrasting second or middle dance appearing between two statements of a principal dance, such as a
minuet or
bourrée. This second dance was originally called a trio because of the 17th-century practice of scoring it for three instruments, and later examples continued to be referred to as trios, even when they involved a larger number of parts. The Menuet of Bach's
Brandenburg Concerto No. 1 (1721) is a late nod to the original practice, with trios for two oboes and bassoon as well as two horns and a third part played by three oboes in unison. 19th-century forms derived from the minuet, such as the
scherzo, also often contain contrasting trios. It usually has a lighter texture than the principal statement of the dance or march. The term is also used for the contrasting section of a
march, the middle section in a march with da capo or the final section of one without. March trios in major typically modulate to the subdominant of the principal key. == Ensemble ==