In music, syncopation involves a variety of rhythms which are in some way unexpected which make part or all of a tune or piece of music off-beat. More simply, syncopation is a general term for "a disturbance or interruption of the regular flow of rhythm": a "placement of rhythmic stresses or accents where they wouldn't normally occur."Syncopation is used in many musical styles, and is fundamental in styles such as ragtime, jazz, jump blues, funk, gospel, reggae, dub, hip hop, breakbeat, UK garage, dubstep, drum'n'bass, progressive house, progressive rock / metal, djent, groove metal, nu metal, samba, baião, and ska. "All dance music makes use of syncopation and it's often a vital element that helps tie the whole track together". In the form of a back beat, syncopation is used in virtually all contemporary popular music.Syncopation has been an important element of European musical composition since at least the Middle Ages. J.S. Bach and Handel used syncopated rhythms as an inherent part of their compositions; Haydn used it to create variety. Syncopation was used by Mozart, Beethoven, and Schubert, especially in their symphonies, for both purposes. This can be heard in Mozart's 38th and Beethoven's 7th. Syncopation is an essential part of the character of some musical styles, such as jazz and ragtime. Hungarian Csárdás song-dances are always syncopated. The "Scotch snap" of Scotland also feature syncopation. Syncopation can also occur when a strong harmony is placed on a weak beat, for instance when a 7th-chord is placed on the second beat of 3/4 measure or a dominant is placed at the fourth beat of a 4/4 measure. The latter frequently occurs in tonal cadences in 18th and early 19th century music and is the usual conclusion of any section.A hemiola can also be seen as one straight measure in 3 with one long chord and one short chord and a syncope in the measure thereafter, with one short chord and one long chord. Usually, the last chord in a hemiola is a (bi-)dominant, and as such a strong harmony on a weak beat, hence a syncope.