Editing Rhythm (section)

===Alternation and repetition===
Rhythm is marked by the regulated succession of opposite elements: the [[dynamics (music)|dynamics]] of the [[Accent (music)|strong and weak]] beat, the played beat and the inaudible but implied [[rest (music)|rest beat]], or the long and short note. As well as perceiving rhythm humans must be able to anticipate it. This depends on [[repetition (music)|repetition]] of a pattern that is short enough to memorize.

The alternation of the strong and weak beat is fundamental to the ancient language of poetry, dance and music. The common [[Foot (prosody)|poetic term "foot"]] refers, as in dance, to the [[Arsis and thesis|lifting and tapping]] of the foot in time. In a similar way musicians speak of an [[Beat (music)#Upbeat|upbeat]] and a [[Beat (music)#Downbeat|downbeat]] and of the [[Beat (music)#On-beat and off-beat|"on" and "off" beat]]. These contrasts naturally facilitate a dual hierarchy of rhythm and depend on repeating patterns of duration, accent and rest forming a "pulse-group" that corresponds to the [[foot (poetry)|poetic foot]]. Normally such pulse-groups are defined by taking the most accented beat as the first and [[counting (music)|counting]] the pulses until the next accent.{{sfn|MacPherson|1930|p=5}}{{harvnb|Scholes|1977b}} A rhythm that accents another beat and de-emphasises the downbeat as established or assumed from the melody or from a preceding rhythm is called [[Syncopation|syncopated]] rhythm.

Normally, even the most complex of meters may be broken down into a chain of duple and triple pulses{{sfn|MacPherson|1930|p=5}}{{sfn|Scholes|1977b}} either by [[Additive and divisive rhythm|addition or division]]. According to [[Pierre Boulez]], beat structures beyond four, in western music, are "simply not natural".{{sfn|Slatkin|n.d.|loc=at 5:05}}