Thommessen has played a significant role in aesthetic discourse in Norway and is known for his modernist and atonal stance.

In later life he has become known for engaging in a critical public dialogue with his former student Marcus Paus about the future of art music, that has resulted in the opera monologue The Teacher Who Was Not To Be with a libretto by Thommessen; a 2015 debate between the two was described as "the biggest public debate about art music" in Norway since the 1970s.

Thommessen has also been active in stylistic and aesthetic discourse and is regarded as a critic of non-modernist and tonal music.

[4][5] The opera monologue was included on the album Requiem/Trisyn/Læreren som ikke ble (2022) alongside the work Requiem by Marcus and Ole Paus.

I write to you based on your presentation in the Norwegian Composers' Association, where you tried to act as a "breath of fresh air" in an environment that you believe has been led astray.