Music theory is much maligned and misunderstood subject these days. This probably comes from it having become in academia at least, an end in itself.
Music theory and jazz theory is a tool-a method for breaking a piece into its most basic elements so that it can be better understood.
Better understood for what reason? So that you can improvise on it, (as in the case of a jazz musician) or so that it can be interpreted in a way that makes sense (in the case of a classical musician).
To a composer, it is a methodology for organizing sounds into something that most people can recognize as music.
Mind you, it is not the ONLY way to organize sound, nor is western music theory inherently superior to the many other methods that exist in other cultures, or that have been developed by the more avant garde musicians in this culture.
It is however, the most common and in the Western Hemisphere at least, the most agreed upon, especially when one is talking about listeners.
What do I mean by music theory? Just good old classical theory along the lines of Hayden, Mozart, Beethoven, Walter Piston, etc. etc. and the logical expansions made of this system by jazz educators like John Mehegan, David Baker and John Novello.
Jazz Theory is really nothing more than Classical Theory modified slightly and added to so as to facilitate improvisation.
Too many musicians shy away from Music Theory thinking that it will somehow straightjacket them and suppress their creativity. A lot of this think comes from the idiotic idea that you are somehow "born" with musical ability, that it's not a skill that you learn and work at.
Nothing could be further from the truth, and the so called "experts" who push this viewpoint do so out of a hidden hatred for any form of art. These are the same guys who will tell you that you can't be a good musician without becoming a drug addict first.
If you want to become a