In music, notes inégales is a performance practice, mainly from the Baroque and Classical music eras, in which some notes with equal written time values are performed with unequal durations, usually as alternating long and short. The practice was especially prevalent in France in the 17th and 18th centuries, with appearances in other European countries at the same time. It reappeared as the standard performance practice in the 20th century in jazz. The phrase notes inégales means "unequal notes" in French. History Pre-modern era The practice of notating pairs of unequal note lengths as pairs with equal notated value may go as far back as the earliest music of the Middle Ages; indeed some scholars believe that some plainchant of the Roman Catholic Church, including Ambrosian hymns, may have been performed as alternating long and short notes. This interpretation is based on a passage in Saint Augustine where he refers to the Ambrosian hymns as being in tria temporum (in three beats); e.g. a passage rendered on the page (by a later transcriber) as a string of notes of equal note value would be performed as half note, quarter note, half note, quarter note, and so on, in groups of three beats. The rhythmic modes, with their application of various long–short patterns to equal written notes, may also have been a precursor to notes inégales, especially as they were practiced in France, specifically by the Notre Dame School. However the gap between the late 13th century ars antiqua use of the rhythmic modes and the middle of the 16th century, when Loys Bourgeois first mentioned notes inégales, is a large one, and little trace of the practice can be found in the fluid polyphony of the intervening period. French origins It was in France, beginning in the late 16th century, that notes inégales began to take on a critical role in performance practice. The earliest treatises that mention inequality of notes in performance indicate that the reason for this practice is to add beauty or interest to a passage which otherwise would be plain. Over 85 music theory and performance treatises from France alone mention the topic between 1550 and 1810, with the large majority written between 1690 and 1780. Within this body of writing there is considerable inconsistency, but by the late 17th century a consensus practice began to emerge. The typical rule, from the late 17th century until