Since it was first coined about 30 years ago to describe a faster, grittier brand of punk exemplified by the likes of Bad Brains and Black Flag, the term "hardcore" has come to suggest an ever-widening range of music. As more and more bands progressed beyond the limiting, often dogmatically rigid parameters of the genre, a new classification emerged: "post-hardcore," a tag that is often ascribed to Seattle quartet These Arms Are Snakes. Naturally, the boundaries of post-hardcore can be confusing, as the emergent genre spans anything from Fugazi to Helmet to Shudder To Think to Drive Like Jehu, and includes an infinite spectrum of variations in between.

But, as much ground as it covers, post-hardcore may no longer be a suitable descriptor for the reach of today's crop of hardcore-descended bands. While keyboard atmospheres churn and throb behind wailing guitar, strangely melodic yelling, and a bass-and-drums attack built on finesse and aggression, These Arms Are Snakes is, along with various peers, heralding yet another philosophical sea change in a hardcore community that now bears little resemblance to its origins. Like The Mars Volta, Portugal The Man, Past Lives, and a growing contingent of colorfully diverse groups, These Arms Are Snakes embraces a dizzying array of influences.

Now on its third album, last year's "Tail Swallower and Dove," These Arms Are Snakes has already established a career routine of more or less casually re-inventing itself with each new release. Apparently, the band's method of making albums - short, pressurized periods of songwriting that take place just before it's time to record - ensures fresh results every time.

"The one advantage to the fact that we tour a lot and have to cram all of our writing into these short blocks of time," explains bassist/keyboardist Brian Cook, "is that it puts these long gaps between our creative periods. The whole time we're touring, we're absorbing new ideas and new music. By the time we head back into the practice space, we're sort of sick of what we've been doing. It just inevitably winds up that we move away from what we've done in the past."

"Tail Swallower," Cook explains, was originally conceived as "a move away from ‘ADD rock' - a cross between Can and Wolf Eyes, with obnoxious textures yet a lot of really simple patterns repeating over and over."

He admits that the final product doesn't even come close to that initial vision. But it does immediately demonstrate the band's sense of ambition. At the same time, there are limits, however grudgingly some of the bandmembers accept them. According to Cook, there is a clear-cut divide within the band as to how far it can experiment before certain members begin to resist. With each member pulling in opposite directions, then, and with drummer Chris Common doubling as producer, Cook says the writing process can get rather contentious.

"Steve [Snere, vocals] and I are the bigger record nerds in the band," he says. "We're always like, ‘We gotta do this shit; this shit's trippy.' We're the ones that are more ambitious and trying to keep moving it more and more out there. Whereas Ryan [Frederiksen, guitars] and Chris are like, ‘No, we've got to keep this more structured' so that it's not overly indulgent."

"Like right now," Cook continues, referring to future material, "Steve's like, ‘Fuck it, I want to sound like Suicide. I want to be as minimal as possible and extrapolate on these really basic soundscapes.' Hey, I'm right on board, but I know that, at the end of the day, when you've got four people working on it, it's not going to sound anything like that."

On stage, each member holds his own with equally strong vigor. Watching the band live is akin to seeing four palm trees flail and twist - yet stay firmly rooted - during a gail-force storm. But, where Cook's old band, the legendary hardcore/math-metal outfit Botch, arguably qualified as having one of the harshest, most violently aggressive sounds in hardcore history, the mood at a These Arms Are Snakes show departs dramatically from single-minded brute angst.

Cook doesn't necessarily agree: "I don't know," he says. "I don't think there's a lot of triumph or uplifting moments in our music. It still sounds like lashing-out more than anything else. We tend to be a negative bunch."

Maybe so, but These Arms Are Snakes brings an expanded emotional and musical palette to that negativity. And it goes a long way. Frederiksen, for one, barely relies on riffs or power chords. Like a steroidal disciple of, say, Tom Verlaine, he cuts into the music with brittle, frosty chords. Keyboards - still widely reviled in the heavy-handed, guitar- and rage-driven hardcore mentality - play a prominent role. As do the technical proficiency and meandering song structures of 70's prog rock. Cook and Common both drive the music hard, but with a profoundly supple, even jazzy, touch on their respective instruments, while Snere twirls and struts and grabs his hips in a defiant show of androgynous apoplexy.

No, this isn't your uncle's hardcore. Or even your older sister's post-hardcore.

"The next time we do a record," says Cook, "I would like to see an even larger leap into another style."

Hey, we're right on board, but that sounds suspicious, like Cook says that every time the band puts out an album.

"Yeah," he says, laughing. "I feel like I have. But dammit, this time I mean it."

These Arms Are Snakes

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Thursday, September 24

Bug Jar, 219 Monroe Ave.

7 p.m. | $8-$18 | bugjar.com