The term 'alternative Classical' - or 'alt-Classical' for short - was coined by critic Greg Sandow back in 2003, but like any good meme, it's taken a while to reach wide acceptance.
But there's definitely a movement afoot to adopt 'alt-Classical' as a recognized genre, and I think that's a great thing. Read Anne Midgette in the Washington Post (Sandow's partner) for a start. Jessica Duchen continues the conversation here.
I think it is wrong to think of alt-Classical as purely a new name for Contemporary Classical music - it's much broader than that. It's more of a reflection of a whole new dynamic for presenting music that's rooted in or derived from a Classical tradition, and can refer to the presentation, the context of delivery, the actual music or composers themselves, or contemporary performance practice... or indeed any one or any combination of those things.
By extension, I think it's also wrong to depict alt-Classical or post-Classical as a kind of 'secondary sub genre' to the traditional Western Classical Canon. To the contrary, it is gradually going to become the primary 'contemporary art music' of our time. Arguably, any composer writing today in a style that's more advanced than Classical- or Romantic-period pastiche could be described as 'alt-Classical' or 'post-Classical'. For those who feel the compelling need to assign genres, calling a composer 'alt-Classical' shouldn't be a problem, regardless of whether they're atonal maniacs or diatonic mavens!
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The broader existing problem is that the system we had in the late 20th Century allowed mainstream Classical to dominate to such an extent, that the 'fringe' of the Classical genre - which included avant garde and contemporary groups, but also smaller organizations and individual artists who pushed the boundaries of how 'Classical' was defined and presented - found it hard to gain the oxygen of publicity that their ideas needed for wide acceptance.
With the internet came the grassroots movement that so perfectly fitted and enabled genres like alt-Classical to reach the hard core fans that they needed. And so, there's a very healthy scene of alt-Classical today, ranging from Le Poisson Rouge and Classical Revolution in the USA, to This Isn't For You, NonClassical, and the OAE's Night Shift in the UK. They thrive through local networks, and digital networks such as MySpace and Facebook too (hence why I've invested all this time into MusBook; I seriously believe a social media network dedicated to Classical/Jazz/Contemporary music will make it even easier for fringe/alt-Classical musicians and fanbases to connect effectively).
Once again, we should relate these changes to what's going on outside of music, in order to gain a better understanding of where our contemporary performance practices are going. This inversion of hierarchy is exactly what enabled Barack Obama to come to power so dramatically, causes rebellions in Iran, and allows for the shockingly quick growth of new web 2.0 services.
Technology is leading musical evolution like never before, and we must pay attention to what's going on outside musical artforms in order to understand how music might develop next.