I'm trying my hand on a little essay here, hoping it will spark an interesting discussion.
What makes music "modern"? People of all ages have tried to answer that question, and depending on their positive or negative associations with the term "modern", their answers vary wildly - but giving an exact definition proves to be far from easy.
The main problem is that when talking about modernity in music, people are tempted to think in terms of stylistic eras and pivotical years, strapping all music written in a certain period to the procrustus bed of the "prevalent" style in that period and chopping everything down to size. For instance: the Romantic era ended in 1910 (didn't it?), so Elgar was a traditional composer, since he remained faithful to his "oldfashioned" style till his death in 1935. Right?
I grew to think that this approach doesn't do justice to the individuality of composers of our time - of all times, actually. It's a totalitarian way of labeling composers, branding them "conservative" or "progressive" based on very, superficial and simplified traits. I won't deny that the concept of stylistic eras can be useful in education and in order to give a beginning listener some anchors for determining the style and historical period of a piece. And yes, if you zoom out far enough, most composers in the past do fit in the general schemes: baroque, classical, romantic and ... modern?
It's in the 20th century when it goes haywire. And there's a connection between composers refusing to get branded with the traditional labels and the finally established individual freedom of artists (and of people in general) that's justly recognized as the most important achievement of our Western civilisation.
Still, composers in the 20th century get the same treatment from musicologists as their older colleagues from the 19th and 18th centuries: depending on their music being more or less "harsh to the ears", they're getting the "progressive" or "conservative" labels pasted to them like nothing has changed in one, two or three centuries. And those labels aren't exactly innocent. Specially in the 50's, 60's and 70's, when (broadly spoken) everything associated with modernism had positive annotations, while traditionalism reeked of mould and badly ventilated rooms.
So once branded "traditionalist", you got about the same stigma as a victim of the McCarthy witch hunts. It's nothing less than a form of fascism: conform to the norm or be expelled from the realm of Serious Music. See the propagation of serialism by the Darmstadt School. And didn't Schönberg, a generation earlier and in one of his more pompous moods, claim that his style would give German music direction for a thousand years?
Sadly, this attitude lives on to the present day. I remember my unhappy years at the conservatorium, where the composition lessons were given by a person who couldn't think past his own avant-garde doctrines, and who couldn't imagine good music being written in anything but the prevalent "modern" style of those days (I'm talking about the early 90's now, when "New Traditionalism" was a rising force, causing the old avant-gardists become traditionalists themselves, in a strange reversal of fortune.) Nothing I ever wrote was modern enough for him - and consequently it wasn't good enough either.
I saw other people in my composition class turn into clones of the great avant-gardists of the 60's and 70's, studying and copying their styles and truly believing being original and progressive by doing so, even if they produced nothing but pale carbon copies.
I was lucky enough to be exposed to another musical world, far away from the repressive incestual sect of the avant-gardists: the world of church music, choirs and organs. Writing music for everyday use has been a revelation: what's traditional in the eyes of one person, can be modern in the eyes of another.
Which brings us to the initial question: what is modern music?
To me, modern music is what the composer himself regards as modern. That sounds like stating the obvious, but it isn't. At first, we have to realize that every composer willingly or subconsciously sets certain limits for himself. Limits like "I won't use those kinds of dissonances" or more generally "I won't go part the stylistic boundaries I've set for myself." Limitations like these help you focus on your own style and give direction to your music writing. Without self-set boundaries, a composer is like a gummy ball, bouncing around in a room where suddenly the walls are removed: you're completely free, but you won't achive anything. Not limiting yourself in any way will effectually paralyze your creativity.
So we have this set of limitations that every composer applies to his own style. Some composers are very aware of this phenomenon, some even apply rigid "methods" to shape their music (like I did in my "mathematical" period in the 90's...) but mostly it's done unknowingly and by intuition.
Now, what makes a newly composed piece of music "modern"? To me the answer is clear: whether the composer has been able to step over his own boundaries or not. Or better formulated: whether the piece made him push his boundaries forward.
Note that this has nothing to do with our traditional way of thinking in historical eras and the stylistic limitations that are imposed upon the composers who live in them. The limits I'm talking about are exclusively personal and individual, and everyone sets them for themselves only.
Seen in that light, the entire output of a composer like Stravinsky can be called "modern", the neoclassical pieces that got criticized so harshly by the avant-garde absolutists included. Why? Because he stepped over the boundaries he set for himself with "Le Sacre" and created a new personal style. It doesn't matter that this new style sounds "older", it's a modern style nevertherless, since it was modern (read: "different") for Stravinsky himself.
The opposite occurs as well, of course. A composer stepping back, leaving his stylistic limitations intact and producing something that's oldfashioned compared to the rest of his output. It happens a lot when composers write music for everyday use, for amateurs or for special occasions. Most of the music I wrote for church choirs falls in this category.
Seen in this light, there aren't any composers who can be called "modern", only individual pieces. And even those pieces can only be called modern compared to other works by this particular composer. Thus the definition of modernity is something that makes the rest of an artist's output look traditional in comparison.
There are no modern composers, just composers whose oeuvres have a high percentage of modern works and a low percentage of traditional pieces, all compared to each other only, and not to the output of his contemporaries. And those composers aren't necessarily identical to those who are called "modern" in the oldfashioned sense of the word. For instance: I'd call most present-day avantgardists "oldfashioned" since they often boast that stylistic limitations don't exist for them. That's nonsense to start with, since they wouldn't even be able to write any music without individual boundaries (see the gummy ball effect I mentioned earlier). And if you chose the most extreme avantgardist style as your personal limit, you end up never being able to cross that limit and hence never produce something truly modern. That's basically the problem with most music that's erroneously called "modern" today.
On the other hand, you have 20th century composers like Britten and Shostakovich, who set personal limit for themselves which were much more close to the 19th century style than their avantgardist contemporaries. Which in turn enabled them to continually step over their boundaries or push them further forward, continually producing works that are truly "modern", in a strictly individual sense.
It's time to change the way we look at composers and music styles, no longer with the desire to label them and pin them down like butterfly collectors, but in a way that does justice to their individuality.