When asked what makes Zeuhl-music so special, one can find a lot of more or less good reasons. A rather holistic answer could refer to the unique combination of different musical elements or to the spirit of it as a whole entity. But looking at some specific elements can also give you a good portion of thrill and a satisfying feeling of explanation why things are great, which is not so easy in rock - as Chris Cutler once said, musicians (and fans too, I think) are afraid that a thing disappears when it gets analysed. Hoping that Zeuhl-music will not disappear whilst I'm analysing it, here are some thoughts about one of the things in Zeuhl-music I like most: the harmonic structures.
What does one have to take care of in terms of harmony if he/she wants to write a Zeuhl-song?
Most important: Never (!) use two normal major or minor chords in a row; if you do this you've arrived in progressive rock like Yes or Genesis, which is not necessarily bad, but it's not Zeuhl-music; at the very least you have to change the bass note.
Looking at the scales that are used in Zeuhl-music, we can find two main directions:
1. Most important is the use of some special scales (let's call them "Zeuhl-scales") that contain as their most unusual element the flattening of the second note: for example 'Theusz Hamtaahk', 'De Futura' (similarly most of 'Üdü Wüdü'), most of the music of ART ZOYD and UNIVERS ZERO contain this really important flattened second, (mostly together with the diminishing of the fifth note of the scale; this diminished fifth can not be viewed as a blue note in the sense of black American music, because the way it is used derives from white European stuff, but that's a really difficult area...). It's one of the most peculiar characteristics of many bass lines in Zeuhl-music and seems to come from 20th Century expressionistic music (Schönberg, Stravinsky, but I'm not to sure about this, as I don't know this music well enough).
2. Also important - mainly in Magma - is the use of different modes of the major scale, often the Dorian mode (most of 'Mekanïk', all of 'A Fiïèh', part of "La" Dawotsin') and sometimes the other modes; here we have a relationship to the use of scales by Johm Coltrane who also played these different modes extensively during his modal period (1960 to 1964/65). Normal major/minor scales and their modes are rarely used by UNIVERS ZERO and not at all by ART ZOYD, I think, which is one of the main differences between Magma and these two classical groups. In OFFERING these scales finally get more important than the "Zeuhl-scales".
What chords are played when using a Zeuhl-scale?
Mostly chords that contain as intervals a minor second or a diminished fifth; often the same type of chord is shifted up and down while the bass pattern stays the same (for example the beginning of 'The Last Seven Minutes').
In groups like ART ZOYD, we sometimes have different tonalities at the same time, especially in their older works; these different tonalities are often represented by different instruments or groups of instruments to avoid an impression of chaos - each instrument's tonality can be clearly located, which seems a great deal to me.
In my opinion, many magic moments in the music of MAGMA deal with the change from a "Zeuhl-scale" to a major scale (or a mode thereof). The change in the middle of 'Theusz Hamtaahk' just before Vander's falsetto solo starts is such a moment; of the same type is the change from 'Cosmos' to 'A Fiïèh' - in both pieces the result of this change from discordant to concordant playing is a great release of tension (and a rebuilding of this harmonic tension, when it's changing again into a Zeuhl-scale).
That, I think, is a more or less small part of the harmonic foundations of
Zeuhl-music, as I understand them. As I'm not an educated musician, I hope there
are not too many mistakes and this stuff remains understandable. I always think
it fascinating to "resolve the resolvable" and see what stays as the real mystery.
Much more could be said about the changing of scales in special pieces and polytonality,
but that's one of the resolvable mysteries that will have to stay unresolved
for the time being...