I can perceive shoegaze, folk-rock, rap-rock, trip-hop, hard-rock, grunge and a lot of rock substyles. But never I found a convincent explanation about the sound of progressive. Could it really just be rock?
Rule 1. There is no convenient explanation of Prog Rock. It can have short songs, long songs, instrumental songs, lots of vocals and harmonies. There can be elements of folk, rock, classical, jazz, and more. Thematically it can be all over the place. Rule 2. See rule 1
To include the whistling of a bird in the opening of a rock song, for example from 1971, would it automatically turn it into a progressive song?
Here's a nutshell definition (believe it or not) that gives three main criteria: (1) The music is attempting to break out of the stereotypical pop/rock music-theoretical structures--to do something different than the typical rhythms (which are usually in relatively simple duple (2-based) or triple (3-based) meters in the stereotypical pop/rock structures), typical harmonic material (I-IV-V, ii-IV-V etc. progressions), typical melodic material (often pentatonics), larger-scale song structures (so not just intro/verse/chorus/verse/chorus/bridge/chorus, etc.), and so on. At the same time, there are still recognizable relationships to those sorts of structures. Note that prog doesn’t require longer song structures, even though that’s found in lots of progressive rock. The reason that many artists did this, by the way, was simply that they became easily bored playing the same ol’ same ol’ all the time re traditional, relatively “conservative” musical material. The musicians in question often had a bit more of a theory background under their belts, and they wanted to incorporate some different ideas into the music to make it more interesting for themselves. This aspect often resulted in the music being more "complex" than normal pop/rock, but it's really not necessary that it's more complex--it's just necessary that it breaks from music-theoretical norms in a way that tends to be literally "experimental" (a la "What would happen if we tried doing this instead of the old cliched thing here?") (2) Most progressive rock artists approached (1) by partially merging rock music with heavy influences from other genres, including classical (from various eras), jazz (again from various eras), world music, etc.--even things like country for some artists. Most artists focused primarily on one other genre to merge with rock, but that's just happenstance. It wouldn't have to be just one merged genre, or even any, really. It could be any number of them. For example, with Yes it was classical (and pretty much oriented towards later 19th century/earlier 20th century classical), with Jethro Tull it was primarily British folk music, with King Crimson, there was a heavy jazz influence, but also a fair amount of modern classical influence, etc. There was a similar reason for this for most artists—namely that the musicians in question were big fans of different genres, and part of breaking the boredom of playing the same ol’ same ol’ was achieved by incorporating various tropes from the other genres the musicians were into. (3) The musicians doing the music either came predominantly from rock backgrounds (so that earlier in their musical experience, they'd played with more straightforward rock bands, they grew up listening to rock and learned a lot about how to play from rock records, etc.). This resulted in the basic "feel" or aesthetic of the music having at least one foot firmly planted in a rock context. Note that jazz-fusion is the flipside of this—(1) and (2) are just as much the case, just where the musicians are departing from jazz norms instead and incorporating other sorts of musical tropes with jazz, and re (3), they’re coming from a jazz background rather than a rock background.
Its really just rock music with a big emphasis on keyboards and complicated time signatures, though there are certainly other aspects to it as well that vary band to band.
I can't easily define prog, but Yes, Genesis, and Rush (despite the assertions of some band members) are prog. The definition gets pretty messy...
It’s better described as art rock and who is and isn’t can be subjective. Queen has songs that border into prog, most notably “Bohemian Rhapsody.” You can define it as rock with theatrical flare and a fantasy-like structure. Some of it borrows heavily on ambience and less on rock, some of it is extremely corny and a mockery of the definition (Styx), and then... there’s Peter Gabriel, and that’s another whole level of insanity to explain!
Good Prog-Rock is unashamedly pretentious. I love many Prog-Rock bands, but some very well-known ones not at all.
Musically, Prog artists deliberately avoided traditional Blues/Rock chord progressions. Among many other flourishes. And the album artwork for sure!
I still don't consider Rush prog, though there were certainly elements of it in a few of their songs. But (for example) name me a single prog tune on side 2 of 2112.
Rock fans must have been wondering how in the world did rock and roll go from Jailhouse Rock and Johnny B. Goode to Tales from Topographic Oceans.
None of the other styles you listed have convenient 1-2 sentence definitions so I'm not sure why you expect that the same could be done for progressive rock. For instances in which you can't tell if a band is progressive rock or not, self identification is a good tie-breaker, especially post 1970s bands. Post 1970s bands that don't self-identify with being part of progressive rock probably aren't.
