Over the years, trying to determine what is true "prog rock" and what is not has become an increasingly tricky proposition.

In the early '70s, it was easy -- any band that performed "suites" that extended across entire album sides and dressed in capes and/or cloaks was a dead giveaway.

However, when the early '80s rolled around, most former prog rockers trimmed out the fat from their compositions (and exchanged their medieval wear and kimonos for what looked like sports coats).

Ever since, there have been bands that have aligned themselves to either of the aforementioned prog rock approaches.

But along came Porcupine Tree, who somehow have found a way to incorporate both into their 2009 effort, The Incident.

Set up similarly to Rush's 1978 classic, Hemispheres, The Incident is comprised of a single long song -- the title track -- that features many different movements (which would have taken up the entire side one back in the good ol' days of vinyl), as well as a handful of shorter compositions that close the album.

The aforementioned title track will certainly be the talk of the album, as it manages to incorporate bombast and melody (the sixth movement, which shares the album's title), rock ("Octane Twisted"), Yes' folky moments ("The Seance"), and Tool-like grooves ("Circle of Manias"), before it all gently floats away on a cloud of fairy dust ("I Drive the Hearse").

That said, unlike early proggers who favored meandering instrumental doodling over succinct songwriting, Porcupine Tree always favor the importance of memorable songs over flashy solos, which certainly makes the group one of the top modern-day prog rock bands.