this thread inspired me to write a few lines about how I see prog music, sorry about that... you can always ignore.
if you want to make a time line maybe you should start with the Beatles doing their orchestral stuff (like Yesterday, Eleanor Rigby). that influenced many people and slowly a new generation of musicians started to blend more sophisticated intrumental to their songs, including organ and other stuff. Some will say its a side effect of the religious feelings arounsed by the LSD ( not lucy). by 1966 there were many groups blending psichedelia and experimental eletronics in their music. that's also when contemporary erudit music like Stokhauser and John Cage became more widely known, the same with some of the most daring jazz like Miles and Coltrane, and again the Beatles brought to surface the oriental music of Ravi Shankar. that highly experimental music found lyric refuge in the literary experiments from the beat generation, anti establishment discourses (remember may '68?), oriental religions, science ficcion and folk tales. so in 69/70's you can say there is a prog scene starting taking shape mixing all those influences.
but it was that Yes redefined the style in 71/72 with their virtuoso musicality, long tracks, eletronic synths (moogs and mellotrons), not talking about the trippy lyrics. that worked for a while and many bands joined the path, making the glory era of the progressive music. but around 76 the pressure of the industry have exhausted the freshness of the style a new and more agressive kind of music emerged from proletarian suburbs and that's when the punk movements started to take over. simpler tunes, less aristocratic instrumentals simply demolished the prog reign. everyone had to adjust to the changes, including the industry that though that was the time for "a more comercial view", "a fresher face"(thank you phil collins). in the 80's even the more orthodox of the proggies had to chang their music -and outfits- if they wish to survive ( and many decided end their activities by then). they joined the industry for a while and many survived. those who noticed the changes coming eventually could adapted earlier, it was the case of Queen or Genesis, some took some time to reshape themselves like Yes, ELP (remember "Touch and Go"?), but in the end every group had to change, because music changed.
personally i like the excesses of the end of the 60's and 70's and even though i lived my young age through the 80's, never really like the sound of the prog bands in that time, too dated to me
