Here's a copy of what I wrote on the PPUSA forum a while ago when General Zod asked "What is Prog?"..................
Ken
First of all, I'd like to say that I'm quite impressed with the responses...especially Ken's (metalprof), Dark One's & Sfarog's...all who have made very good points.
OK...now in an effort to try to keep this as short as possible, I will attempt to respond to Ken's ...hehe. (
OK...looking back after I finished, I guess I failed. 
)
I like the family tree analogy, but would only partly agree. And sorry, I disagree...using the dictionary definition is not futile, when you think of the key word..."change".
As long as a band is doing something significantly different & unique from it's progenitors, I would consider that enough to be called "progressive". Every band is influenced by another in one way or another, so I agree that having some commonalities should NOT disqualify them from being labeled "prog". Plus, one can even argue that all the 70s prog rock bands were influenced by say the Beatles in one way or another.
What I'm merely saying is that a progressive band is a band that adds a significant twist to what came before them, and that they continue to add twists to their own style & music. However, once a band becomes commonplace within themselves (ie DT...originally prog IMO) or among the bands they're associated with, IMO they are no longer considered progressive. Progressive does not mean "same shit over & over".
Also, if a band has ever been considered a "clone" of another band, that immediately disqualifies them IMO...which many of the bands with the prog metal label are...clones.
What I'm also trying to say is that time/generation is also a huge factor...if a band is among the first generation of it's progressive stylings (Yes, Genesis, ELP, King Crimson, Rush, etc...each who are significantly unique in their own way), then they would be considered prog. And, as long as they continue to change, which those bands have (at least for the better part of their careers), then they would still continue to be called prog. Also IMO, I do think, as you said, that progressive DOES in fact mean that a new set of bands (or progression shown through follow-up albums) need to emerge...not every year, but definitely every few years...once a particular progressive styling becomes commonplace.
Now take a band like Sym X for example. All they've really done is take a neo/pseudo classical approach, which has been done by many bands over a decade prior (ie ELP, Yngwie, Randy Rhoads, DT), and added chunkier guitars, an abundunce of keyboards & Dio-esque vocals (none of which unique)....same goes for almost all the similar sounding bands like Angra, Vanden Plas, Rhapsody, etc. Therefore, making them all 2nd, 3rd, 4th, etc generation of that style...added to the fact that they have not strayed hardly at all within their own style...and so, neither by "definition" nor family tree analogy (being remotely linked is definitely not enough, but rather 1st generation of the tree) should they be considered "progressive"...IMO.
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Now, of course I admit that all opinions are completely subjective, and if we don't agree, that's OK...we can just agree to disagree. I just like to shake things up a bit, have a good debate, and hopefully cause people to think...and not just accept/follow, like sheep (sheeple).
If anyone has more to add, please bring it on...this is cool.
