I've always thought there's few stronger indicators of musical kinship with another person than agreeing on the same favourite Fugazi record. Given that they never really made an average album, let alone a poor one, you could easily put forward a compelling argument for any of their six full-lengths - or the compilation 13 Songs, for that matter - being the highlight of their catalogue. For me, at least, it's always been Red Medicine, which turned twenty last month (amusingly, just a day before Alanis Morissette's Jagged Little Pill did likewise.)

This is something that's been of no small bafflement to me over the years; on paper, at least, this album should not be my favourite of Fugazi's. The incandescent, Albini-helmed intensity of In On the Kill Taker is more in line with my usual tastes, as is 2001's The Argument; dark, dripping with atmosphere. Repeater was my introduction not only to the band but to Dischord, too, but Red Medicine even trumps the obvious affection attached to that association. It's a record that feels like an anomaly in plenty of different senses, and one of the few releases ever to have me wondering if there really is some truth in the old adage that writing about music is like dancing about architecture. So much of what makes it great is difficult to precisely lay your finger on.

The tour cycle for In On the Kill Taker had been the band's most ferocious to date, and when they decamped to a remote country house in Guilford, Connecticut to begin throwing around new ideas for songs, they'd begin moving in a direction that Red Medicine heralded the start of and End Hits and The Argument would continue; genuine sonic experimentation. Fugazi remained angry, of course, but the need to make an irascible punk rock statement had been sated by Kill Taker; instead, those writing sessions in 1994 were primarily aimed at the four stretching themselves as musicians, seeing how far they could warp their previously steady punk mould by introducing genuine subtlety and nuance.

What resulted was - to put it bluntly - the weirdest record Fugazi ever made. There were strange instrumental choices - the creepy piano that introduces 'Birthday Pony' sticks in the mind - and bold stylistic diversions. 'Version' is perhaps the ultimate case in point; distorted clarinet playing from Guy Picciotto drifts over the top of what is effectively a nightmarish exercise in melding dub with a freeform jazz rhythm section. Underpinning it all is a squelching keyboard progression that sets the mood - Fugazi had done foreboding before, of course, but never quite like this.

Elsewhere, 'By You' is a five-minute exercise in sheer abrasion, feedback screaming over Joe Lally's vocals to almost psychedelic effect; 'Fell, Destroyed', meanwhile, pitches up at the other end of the spectrum - penned by Picciotto, it was the closest thing to rock balladry they'd ever produced at that point, an idea that you couldn't possibly have entertained with a straight face beforehand. There's still furious interludes harking back to Kill Taker - Ian MacKaye's sub-two minute 'Back to Base' is a good example - but the guitars have been carefully adapted, elsewhere, to fit the experimental ethic. On 'Bed for the Scraping', MacKaye and Picciotto are locked in a battle of free-form melody - another point at which it feels like the album is flirting with jazz - whilst 'Latest Disgrace' is a first Fugazi stab at working with alternative tunings. On closer 'Long Distance Runner', the playing is languid, untethered by structure; it almost sounds as if, by the time they'd reached that song, they'd shaken off their old rigidity entirely.

The brilliant thing about Red Medicine is that, in 1995 - before End Hits and The Argument had proven that this new, more experimental direction was to be a long-term pursuit - it might have been easy to pigeonhole the album as being a straightforward reaction to the fact that the sound that they'd made their signature during the alt-rock boom of the early nineties was beginning to be co-opted by bands with commercial aspirations, not to mention major labels, who were picking up bands like Jawbox and Shudder to Think almost at random, without any real clue about how best to go about managing them.

Whilst there are lyrical nods to this situation on Red Medicine - particularly on 'Target', where Picciotto rages against "marketing the use of the word generation" - the actual fact of the matter if that this was the album on which Fugazi moved past being viewed as a band tied intrinsically to its politics, that had little to offer musically beyond the taut temper of their earlier albums. They didn't necessarily mean to make a statement, but simply by trying to push their own boundaries, they did; Red Medicine is erratic, taking risks from start to finish, but it elevated its creators above so many of their peers and positioned them as one of America's most vital rock bands on their strength of their songwriting ability as well as their ideology. There's nothing in the Fugazi catalogue that sounds dated yet, but Red Medicine still sounds as if it has one foot in punk's future, two decades on.