Structural elements of music: rhythm
Everything around and within us pulsates and unfolds cyclically over time: the stars, the seasons, the waves in all their forms, our heart, the rhythm of breathing. To fly, birds and insects must flap their wings with a regular frequency, the sound itself is vibration, pulsation. When we walk, run, speak, we take a rhythm. And what about dancing? What better expression, made through the human body, of rhythm, of movement organized over time.
All this naturally reverberates in musical practice, the sound is indeed structured in durations based on a pulsation (beat) that is called isochronous (from the Greek isos = equal and cronos = time), in practice a beat that repeats at regular intervals over time.
This isochronous pulsation is so fundamental that musicians study it with the use of an instrument that reproduces it specifically: the metronome.
Rhythm is everything and everything is rhythm, it is the most important element of music (and of life), everything moves pulsating. While music can be made based only on rhythm (with structures usually made of percussive sounds laid over the isochronous pulsation or beat), on the contrary it is not possible to compose pieces of music based solely on melodies or chords without the rhythmic element (although of course there are interesting musical experiments of all kinds).