There is a moment in every bit of stage magic of suspended certainty in which suspense takes over, the spell has been cast, but neither the magician nor the audience can be certain that something — indeed, anything — will happen. For the audience, it is the moment in which the build-up to the illusion reaches its peak, to be followed either with surprise and admiration, or by disappointment or even dismay, while for the performing magician that peak is one of anxiety, for no amount of practice and discipline can always insure a satisfactory rather than disappointing result. Ta-dah.
Musical composition and performance has much in common with the invention and discipline that go into theatrical conjuring, but for my money, music has an unbeatable advantage over stage magic in that the goal of the stage magician is not to be surprised himself, but to command and control the situation so that the audience will reliably be surprised. Music, however, has a way of reliably surprising both author and audience and, indeed, I think that the best composers have a way of eliciting such moments, however risky. (A repo man spends his life getting into tense situations.) Moreover, while stage magic leaves the audience with no illusions (bag full of tricks understood), with music at its best, there is no reasonable expectation that any trickery be explained away.
Musical surprises may be modest. I remember, for example, as an earnest undergraduate, talking with Philip Glass after a solo concert in Santa Cruz. He was excited about the woodwind, organ and string orchestration for then-new score to Satyagraha which turned out to have a lively "buzzy" (his word) quality that surprised him. Of course, as a musician with his training and experience, Glass knew all of the elements that went into that orchestration, and he had his expectations, but the result still surprised, and still does surprise.
Sometimes the surprise is rather more fundamental in character, shaking the composer's own idea of the piece. Alvin Lucier's Septet is a good example. The piece, in which wind and string players play long tones a precise small intervals from a standing sine wave tone in order to create patterns of interference beatings, worked at its first performance, by a group of fine players who had much more experience with standard classical repertoire than with experimental music, but it was more-or-less just another Lucier piece about beats. However, some years later, the piece was taken up by an ensemble in Berlin which had the time to really live with the piece. The players discovered that they could just focus a bit more on shaping dynamics, smoothly curving them in gradual crescendi and diminuendi over the course of each long tone and that, suddenly, certain harmonics of the instrumental tones would just pop out of the texture. The piece was doing something unintended by the composer and it was beautifully so. This phenomenon could have been anticipated — even calculated, with some spectrograms and a critical band chart — as it was always implicit in the set-up of the piece, but it took a particular kind of engagement with the work to actually discover and bring the phenomenon into focus.
Part of Lucier's legerdemain — in this piece and in others — is the move of saying that "this piece is about x" (in which X can equal acoustic interference beating or room resonances or feedback etc.) and — strategically, depending upon the composition — implicitly or explicitly putting other aspects of the piece into the "not about" box. In some cases, this is genuine sleight-of-ear stage magic: in I am sitting in a room (the one opera that will certainly survive from the 1960's) the piece is explicitly about a particular process but the composer's patter directing you in one way cannot but help the listener from also taking in elements of the piece — in particular a certain emotional drama — which he would appear to be excluding.
With surprising frequency, when a composer says up front that "this piece is not about x" or "I'm not interested in x", element x suddenly becomes very, even urgently, interesting. (It's somewhat like telling someone to "relax!"; given such an instruction, relaxing is just about the last thing you can be expected to do. A composer can ignore this likelihood or perhaps usefully work with it. There's a very nice conversation online between the composers Michael Pisaro and Aaron Cassidy (at Tim Rutherford-Johnson's Rambler blog, here) which, among other things, is a useful illustration of some of the rich territory which experimental music and high complexity share. In it, Cassidy describes tablature scores in which the precise pitch produced is explicitly not the material of the composition, not the compositional subject of the piece. Nevertheless, once realized in performance, doesn't pitch inevitably become one of the most interesting aspects? Now, these aren't pitches representing a precise compositional design, but for all the variations in detail there are inevitably global features to the pitchiness that are composed and it's not altogether important whether this is legerdemain or laissez-faire.
One more remark about this common territory between experimentalists and the complexity crew. I've written here recently enough about complexity, so won't bore you further. This territory also has common parts with the big computer people and the small computer people, and folks that build new instruments, whether powered by breath, muscle, 9 volt batteries or the power mains or those who make installations or recordings or online-ables in preference to concert music. This fractiousness doesn't strike me as very useful to anyone, except in the narrow musical-political function of sorting out grants, prizes and positions. It just doesn't have much to do with music and, critically, with the tendency of camps to produce more camp followers than adventurers, it doesn't have much to do with making innovative music in particular. In an era of increasingly limited resources, this is a serious practical mistake, for it will tend to suck in the mediocre but similar while excluding the extraordinary but varietal. Fortunately, there are examples of composers — Christopher Fox is a good example — who have always been comfortably apart from attachment to a particular camp, finding musical goodwill and utility across these demarcations, and there are even some good signs of thaw from the most stalwart figures (e.g. if nothing else, the non-specified instrumentation of Ferneyhough's Bone Alphabet was a friendly gesture in the direction of the experimental tradition.)