Rhythm (from Greek ῥυθμός - rhythmos, "any measured flow or movement, symmetry") is the variation of the length and accentuation of a series of sounds or other events.
The study of rhythm, stress, and pitch in speech is called prosody; it is a topic in linguistics. Narmour (1980, p.147-53) describes three categories of prosodic rules which create rhythmic successions which are additive (same duration repeated), cumulative (short-long), or countercumulative (long-short). Cumulation is associated with closure or relaxation, countercumulation with openness or tension, while additive rhythms are open-ended and repetitive. Richard Middleton points out this method cannot account for syncopation and suggests the concept of transformation.
A rhythmic unit is a durational pattern which occupies a period of time equivalent to a pulse or pulses on an underlying metric level, as opposed to a rhythmic gesture which does not (DeLone et al. (Eds.), 1975,
Musicians make rhythms with musical instruments. A musician's role is to perceive and measure time. They consciously feel, shape, divide, and compose time to convey feeling. All musicians, instrumentalists and vocalists work with rhythm, but in modern music a rhythm section generally consists of percussion instruments, bass and possibly chordal instruments (e.g., guitar, banjo) and keyboard instruments, such as piano and organ. In recent years, music theorists have attempted to explain connections between rhythm, meter, and the broad structure and organization of sound events in music. Some have suggested that rhythm (and its essential relationship to the temporal aspect of sound) may in fact be the most fundamental aspect of music. Hasty (1997, p. 3), for example, notes that "Among the attributes of rhythm we might include continuity or flow, articulation, regularity, proportion, repetition, pattern, alluring form or shape, expressive gesture, animation, and motion (or at least the semblance of motion). Indeed, so intimate is the connection of the rhythmic and the musical, we could perhaps most concisely and ecumenically define music as the 'rhythmization' of sound." Another piece of evidence suggesting that rhythm is the most fundamental aspect of music is that percussion instruments were likely in use long before stringed instruments. Tribal groups dancing to music made only with percussion instruments is an ancient human practice, which reportedly continues today. The three fundamental elements of music are rhythm, intervals, and chords.