The Swiss composer and pianist Ernst Lévy (1895-1981) is probably best known within the world of oddball music theory as the progenitor of the concept of "negative harmony," which he introduced (though not by that name) in his innocuously titled treatise, A Theory of Harmony, written in French in 1940-41 and published in English translation only in 1985. Lévy's idiosyncratic approach to harmony is based on the principle of inversion, or changing the direction of intervals around a designated axis. This technique allows for the creation of "mirror" versions—audibly related yet formally distinct—of any collection of notes, from melodies and chords to entire pieces. It's an ingenious extension of the resources of tonal music, which can be used both as a compositional tool and as a way of creating alternate-reality remixes of existing tunes. (The keyword is "negative harmony" if you would like to take a trip down this musical rabbit-hole.)
Lévy's writing mixes technical neologisms ("telluric gravity" being my favorite) with metaphysical speculations and epigrams from pre-Socratic philosophers. His philosophical stance is refreshingly distant from the pseudo-scientific pedantry of so much music theory, as evidenced by this quote:
"Music is not, as some contemporary acousticians would like us to believe, 'something that happens in the air.' It is something that, first and last, happens in the soul. To an inner, spiritual something corresponds an outer, physical something: tone. Music happens when both are 'attuned' to each other."
Not much information is available about Lévy's music, and only a handful of his compositions seem to have been recorded. According to the liner notes to the LP recording of Lévy's Fifteenth Symphony (1967), the composer believed that "music is basically not a communication system... He did not see his music as a kind of code used to convey messages to an audience. Music for Lévy was rather a kind of communion through which his philosophical worldview and musical universe could be shared with others."
Lévy's music, as suggested by this movement from his 1980 composition Sonata for Ten, is obviously tonal (or perhaps better put, neo-tonal), but in a peculiar way. Though it has a "composerly" polish that makes it approachable for classically conditioned listeners, this is music that finds new passages through tonal space, moving by unexpected strides and opening doors that our ears had not seen.