I'm sorry, Lorenzo. My mention of The Mothers' Freak Out was meant to imply this discussion's previous mentions of songs/sides from The Mothers' 1966 album--specifically the mention of "The Return of Son of Monster Magnet" on the band's concept double album.

As to my other mentions, I guess I'm expressing my interest in the impetus for the formation/creation/adaptation of the suite/epic/jam format that eventually became so much associated with progressive rock music--the topic you started. It is a topic that I have been researching for some time now--and which seems to have its roots in classical music forms (symphony, sonata, opera, etc.) but also in the classical Indian music that the West had been exposed to by the extensive touring (and album releases) of Ravi Shankar and Usted Ali Akbar Khan as well as from the minimalist explorations of Terry Riley, Paul Bley,  and others and the influx of African musical traditions as explored and expressed by the jam sessions and teachings of Babatunde Olatunji. 

The influence of Indian and African musical traditions is well accounted for in the notes and interviews of many artists who later wandered into and under the "progressive rock" umbrella--a web that has already been stretched on this site by the inclusion of the likes of 1950s Miles Davis and 1960s Herbie Hancock. The influence of Ravi Shankar's music and John Coltrane's "India" on Roger McGuinn's creation of the first psychout song ever--"Eight Miles High"--is well documented. We know that two of the side-long epics of The Soft Machine's ground-breaking album Third come directly from the influence of Terry Riley and Miles Davis.

     Keith Emerson and Mont Campbell were obviously trying to follow established forms with their Nice Ars Longa Vita Brevis and first Egg albums, respectively.

     Iron Butterfly were undoubtedly inspired to jam while under the influence of a particularly hypnotic groove (probably the Doors' "The End"). 

My point is: It is so very hard to delineate the "start" and the "precursors" of progressive rock music when it doesn't come from rock music, it comes from the melding of many forms and influences. I love the discovery of these influences--of the pioneers' stories of where their ideas came from. So, thanks for starting this thread. I'm sorry if it's become a slog.

Oh, and I forgot to mention the influence of UCLA student trumpeter Don Ellis on others when he and his new fascination with odd time structures (gleaned from his Indian professor Harihar Rao, a student of Ravi Shankar's), and what evolved out of their school band, The Hindustani Jazz Sextet. Don's Orchestra's performance at the 1966 Monterey Jazz Festival is legendary. So many people claim to have been blown away by his band's "show stopping" game-changing performance with its incredibly unusual time signatures and unusual stage presence of three bass players, three drummers, organ, vibes, and vast horn section. The 1967 album "Live" at Monterey Jazz Festival captures some of their performance. Who knows, maybe Frank--or one of his future band members--was there. We know Ralph Humphrey was--and even became a Don Ellis Orchestra drummer after the car accident took teenage drumming phenom Steve Bohannon out of the picture.

While the four jams on 'Live' at Monterey are not side-long, they definitely stretched space allowed on the standard vinyl album: with 39:18, he was definitely pushing the then-known limits of vinyl pressing!

Read the thread, and then I hope for you that you understand the answer. 

What does that mean? 

I'm just enjoying the music without wishing to get Entangled in the back and forth debate about what does and doesn't constitute a suite.