Struggling with this (whilst liking [periods of] Genesis, Rush, Pink Floyd, BJH, Supertramp, etc.).
How the hell is 'progressive rock' defined - this is such a vague concept? [anyone?]
And, obviously, a band can be labelled 'progressive' and then [albeit, usually with personnel changes] become not prog. Should be 'progressive music' rather than progressive bands.
Arguably [and already mentioned once or twice] The Beatles were the most progressive band ever [but would never be labelled a progressive rock band]. Oh, and The Velvet Underground.
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I kind of dislike bands such as Rush, Genesis, BJH, Pink Floyd being labelled 'progressive'.
The term 'progressive' for me is associated with the long, indulgent, lacking focus, 'dinosaur' rock that was called out (or pushed underground) by punk (according to the mainstream narrative).
I think a number of bands are considered 'progressive' until they learn their craft and learn how to write proper songs. - I know! - just a point of view [and not even one that i fully endorse - I like some of these bands' early stuff].
Maybe I shouldn't have added to this thread (though the five bands listed above are in my top ten favourite bands). I am coming at the subject from a somewhat limited / narrow perspective, I guess.