How to define and classify progressive rock?

I'd like to post some remarks about the article in its current state.

First of all, I'm the author of the Russian wikipedia article on progressive rock. The article isn't a translation of the English one, but instead is based on a book by Valery Syrov, a Russian music theorist. The English info about the book is here. AFAIK it's unavailable in English. And though he distinguishes between prog and art rock, I'm using in my comment my own interpretation of the issue with both his prog and his art rock being termed "prog".

And in this book, written in 1997, he is using the very same idea of "prog-is-synthesis". I can even remember he probably doesn't attribute this idea to himself, but cites some Western scientists. He uses the idea only to define prog, but the definition of subgenres is straightforward. He doesn't restrain the genres to be fused with only to the top ones, which immediately eases the addition of the Heavy prog subgenre to the classification. However there is no objectively verifyable criterion of prog in the book. He says that prog "is a creative enrichment of rock music via a dialogue with other musical movements" and by "dialogue" he explicitly means something which is the inverse of "shallow copying, simplified reproduction or common blending of genres without attempting their synthesis and comprehension" - some kind of your #2 part of the criterion.

Overall it's a funny read with great ideas like the use of "silence" (interchanging heavy with mellow music - presented in the book by waveform views of the audio files) pioneered in rock by prog and a lot of factual mistakes like asserting Portnoy being Russian by origin...

And there is also another independent comment on the synthesis hypothesis by the Arsenal (band legendary in USSR) frontman: "Progressive rock for the rock music is the same as fusion for the jazz music" (my own translation, as is, no warranty, etc). This IMO doesn't include any analogue to your #2 restriction.

And now my own thoughts on the subject.

Skip this paragraph if it bores you, but just a minor issue:

David_D wrote: The broader “Prog community definition” has obvious advantages: it includes more different music and makes “the Prog movement” wider and thus stronger.

David_D wrote: The main point of this way of defining is for me to separate a large part of the experimental and more ambitious Rock music from the mainstream in order to strengthen its identity and help building it up as a broad cultural movement.

Actually I'd like to have a classification to support understanding of "another" identity. Sorry for the pun, I've just run out of words, but I'm talking about my own identity as a prog listener. What music traits I tend to like? What other albums might have such traits? This is what, say, last.fm tags are about. And this brings me to my own view of an ideal and thus impossible "classification". Just take the last.fm principle of tags instead of hierarchic classification (this kills the eclectic category, which is anyway just a bin for the yet unclassifiable), then decide to tag primarily albums (but also compositions and bands) and use only the objectively verifiable traits as tags. Some examples of "objectively verifiable traits" so that you see why I call it ideal: apart from easy tags like "from Sweden" or "contains a long track", there is a theoretical way to decide some more interesting traits. You can get an educated person to tell the time signatures and if they are changing, and also the musical modes, characteristic note patterns, etc. Another more theoretical way is to try to devise stochastic algorithms to analyze the music as a signal and to say if it contains all the above, or numerous character changes and if these changes are predictable (like in chorus-verse patters) or not. Same thing to see if there are heavy/mellow changes - the last is clearly doable.

I now understand that you consider space-rock as a part of the subgenre "Psychedelic Prog".  "Heavy Prog" is one of your subgenres of Prog as well. 

Perhaps you could supply a listing of your "main genres" and "subgenres" as you currently have them envisioned? 

Main Genre list:  Classical music, jazz music, ethnic music, electronic music, and avant-garde music.  Are there any new additions?

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