Since the 20th century, it seems the genre of folk has splintered off in interesting ways. Most people use it lately to describe the acoustic stylings of bands like Iron & Wine, who grew to fame after being featured on the Garden State soundtrack. There's been plenty of talk over the term "folktronica," also known as "freak folk," which includes the weirdness of Animal Collective and the latest efforts from Sufjan Stevens. But sometimes the roots in actual folk seem to go missing. Sam Beam writes songs with pretty standard rock chord progressions. His gentle delivery and low-fi acoustic aesthetic seemed to be all he needed to land him the "folk" modifier (back when Iron & Wine was still unplugged). The use of "traditional" instruments doesn't seem to be a requisite anymore; all you need these days is an acoustic guitar and a beard. 

The contemporary methods of defining genres like folk seem to focus more on tone than actual structure or instrumentation. Bonnie "Prince" Billy, the lesser-known but more important precursor to Iron & Wine, has similarly landed himself in the realm of indie folk, as it were. Lately his efforts have steered more to the country side of things, but his seminal release I See A Darkness is lauded as essential contemporary folk rock. Will Oldham does break out the more traditional string instruments on occasion, but for the most part his repertoire is soft rock edged with an Appalachian twang.

On the other side of the ever-broadening folk spectrum, we have genre mashups that draw not at all from the gentle tone of folk as we think of it, but from its instruments, structure and sonic textures. There is such a thing as folk metal now, and it is awesome in entirely new ways. Bands like Finntroll play accordions over their power chords, drawing out the celebratory energy from old-school European folk, i.e. polka. Yes, there is polka metal. That is a thing that exists. Finntroll hail from Finland, though, and folk metal does seem to be a uniquely European creation. Their lyrics draw on folklore and fables, notably those about trolls, as you might have guessed. Despite the strangeness of combining folk music with something as traditionally aggressive as metal, Finntroll might actually be truer to the history of folk than many contemporary American bands. 

It all comes down to what's more important in defining genre: the overall "sound" of a band or the concrete components of their music. Finntroll appropriates parts of folk for their own sub-genre, branching out into something more akin to historical fiction than an actual embodiment of folk. Sam Beam and Will Oldham might not even be interested in folk historically, but get pegged into its latest incarnation due to surface aesthetics. Who's to say which, if either, has more right to the title? Both styles produce great tunes, and for the first time in history, we can mosh to songs about trolls. I'd say we've come pretty far. 

Sources and photo credits:

http://en.wikipedia.org/wiki/Folk_music

http://en.wikipedia.org/wiki/Folk_metal

http://en.wikipedia.org/wiki/Finntroll

http://earlyjouvertmorning.com/2010/11/08/upcoming-releases-iron-wine/

http://www.aquariumdrunkard.com/2008/07/03/bonnie-prince-billy-wilding-in-the-west-live/