Some artworks—works of music, theatre, dance, and the like—are works for performance. Some works for performance are unperformable.
Some such works are unperformable by beings like us; others are unperformable given our laws of nature; still others are unperformable given considerations of basic logic.
Musical works that fit into each of these categories really are genuine works, musical works, and works for performance, and the very possibility of such works is ontologically significant. In particular, the possibility of these works raises serious problems for type-theoretic accounts of the ontology of music as well as certain mereological or constitution-based accounts.
This according to “Unperformable works and the ontology of music” by Wesley D. Cray (British Journal of Aesthetics LVI/1 [January 2016] pp. 67–81.
Many thanks to Improbable Research for bringing this to our attention! Above and below, György Ligeti’s Étude No. 14A: Coloana fara sfârşit (Column without end), one of the works discussed in the article.
György Ligeti freely acknowledged the influence of African music on his work—an influence that is seldom readily obvious, though it can be teased out by analysis.
After he listened to recordings of African drumming, Ligeti began exploring the use of various rhythms through multiplication of the basic pulse, a concept that resonated with the additive rhythms of the traditional music that he grew up with in Hungary.
In one of his few passages involving the use of an African-sounding instrument, the third movement of Ligeti’s piano concerto includes an Africanesque pattern played on bongos. He marked the part to be played very quietly, so rather than being foregrounded it serves almost imperceptively to reinforce patterns being played simultaneously on other instruments. Unlike most African drumming, this bongo pattern evolves over time, so that its end is quite different from its beginning.
This according to “Ligeti, Africa, and polyrhythm” by Stephen Andrew Taylor (The world of music XLV/2  pp. 83–94).
Today is Ligeti’s 90th birthday! Below, Mihkel Poll performs the movement in question.