Slack? Jackie-O Motherfucker? Well, yeah, group leader Tom Greenwood will admit to being slack. While many bands and listeners place a premium on being "tight" (this is one of those ultimate adjectives that many people reserve for musicians), the Portland collective, by contrast, operates with the opposite impulse in mind: This ever-­morphing, mostly improvisational unit's work can be very loose and seemingly shapeless. Even the more structured pieces—essentially folk songs with their roots in deep space—have a lackadaisical air about them, languidly spooling out as if we weren't living in the accelerated 21st century and miraculously had more time than we knew what to do with.

"We get repulsed by things being tight," a jet-lagged Greenwood states via e-mail from Japan, where JOMF are just starting a four-date jaunt in Tokyo and Osaka. "For me, it's a physical reaction. It's always been like that. We build it to break it apart, and sometimes we can't even be bothered to build it very well. The structure needs to be at least slightly off for it to work. I know it doesn't make sense. But it's not lackadaisical. It's part of the intent, the will, the volition... we want to move around in a space that is free. For me that is a premium; maybe that's too much for rock 'n' roll... although I'm betting that it's part of the soul of the art form."

If JOMF's music is loose, their lineup may be even looser. Greenwood is the lone original member, and one of his key creative foils, Honey Owens (who also records haunting space blues as Valet), comes and goes like a wraith. Sadly, she won't be accompanying JOMF on this tour supporting Yo La Tengo, but guitarists Brian Mumford and Nick Bindeman and drummer Danny Sasaki will be.

"Honey is busy with many things... she is a woman of mystery," Greenwood notes. "We work with her on her own terms, and that has provided us with a long working relationship—and a great friendship!

"For better or worse, JOMF is a ship adrift, and we prefer to work this way; we don't gather internal resentments, and the band is stronger for being more flexible. That might not make sense, but it works for us."

This MO works for many psychedelically inclined, free-spirited listeners, too. JOMF's best latter-era songs from Flags of the Sacred Harp, Valley of Fire, and Ballads of the Revolution arise from a template that runs in the lineage of such sprawling yet tuneful compositions as the Velvet Underground's "Oh! Sweet Nuthin'" (Loaded's valedictory last song), Mercury Rev's "Car Wash Hair" (a swaying sike-pop single by these now-domesticated hellions), and the spectral-blues sigh of Spiritualized's "Shine a Light." This material is shot through with a breezy bliss yet freighted with a profound yearning and sadness.

JOMF's more conventional leanings surface on tracks like "Lost Jimmy Walen" (off The Blood of Life), a trad ballad played straight and forthright. Earlier full-lengths like 2000's Fig. 5 and 2001's Liberation find JOMF in more fiery free-jazz/improv/musique-concrète mode while also retaining their predilection for slow-building, spaced-out trance jams—see especially the 14-minute "Ray-O-Graph" and the 19-minute "In Between." Though not technically "good," Greenwood's voice is an effective vessel of pathos—slightly foghorny and nasal, but not Stipe-ifically so.

Besides being an artist who's comfortable with spontaneous creation and honed songcraft, Greenwood has developed a rep for being difficult. Even JOMF's Wikipedia entry notes this trait: "The group has had more than forty members, most of which have quit due to Greenwood's impulsive behavior." Hmm. Why have so many members come and gone in JOMF?

"Sometimes making good art is messy," he says. "We've been very actively producing music for 15 years, and I'm extremely proud of what we've done. That said, I can also accept and face my own failings and flaws—which are many. I don't care about that description, to be honest. It's fair, I guess, but I'm involved in this because I'm committed to the creative impulse, and process."

Process even a modest chunk of JOMF's vast and elusive discography and you'll notice a gradual drift from freewheeling, jazz-inflected improv to structured folkadelia.

"That's true, to a degree," Greenwood admits. "We are more and more working as two bands in one these days. For a long time, we tried to present totally free music to rock audiences, and it got really weird sometimes—people really hating on us. So now we have learned to use some structure to our benefit and come up with some nice songs in the process. We are presenting this material more for club and festival audiences. We are still involved in our more free/improvisational activity, but we are trying to direct those efforts in a more precise way, through cinema and so on. We've been really heavily involved in this sort of transition of our process this year... hoping to see some results from it with a film score we're working on now."

Maybe Jackie-O Motherfucker aren't so slack after all.