The music of the early 20th century was marked by increasing complexity and abstraction. Serialism and the chance practices of John Cage and his followers created an aesthetic that stood opposed to the Romanticism of the century before. In the '60s and '70s a counter-reaction began to emerge as a new group of young composers sought to free themselves from the strict rules of atonalism and serialism and embrace the simplicity of minimalism.
In 1959, composer Dennis Johnson composed a six-hour work for solo piano simply called "November". With its repeated passages and tonal harmony, many consider this work to be the first minimalist composition.
Terry Riley wrote a piece in 1964 entitled "In C"; which consists of 53 melodic fragments of various lengths. The work could take anywhere from 15 minutes to several hours to perform. It is intended to be played by an ensemble of any size and of any instrumentation. All of the fragments outline a single harmony which is colored by the timbre of the instruments and the motion of the melodic fragments.
A few years later, Steve Reich brought the phase shifting experiments of his tape loops into the concert hall with his "Piano Phase". Two performers play the same melodic figure on a loop. One stays at a constant tempo while the other slowly accelerates. The figure is heard in every possible phase lasting somewhere between 15 and 20 minutes.
Composer Philip Glass began experimenting with additive processes with his work "1+1". One note becomes two, becomes three and each repetition builds on the last.
Repetition is the true hallmark of minimalism. It is also a different approach to harmony and form; The consonant quality of the chords stand devoid of their traditional function. This music isn’t meant to go anywhere, it is meant to be. And in this regard, minimalism has more in common with Eastern aesthetics and philosophy than it does with traditional Western music. It’s about the power of being still in a single moment.
Of course, not all minimalist composers write static music. American composer, John Adams’ 1986 fanfare Short Ride in a Fast Machine was his attempt to take the processes of Minimalism to a more dramatic end.