Most people who decide to play the piano just want to learn how to play the piano. They want to be able to express themselves using the skills they will develop and immerse in the beautiful world of sounds. Music theory on the other hand sounds like a dry, boring, unnecessary and dull way to spend your time. However, I find that theory is an essential knowledge for anyone who would like to develop musical skills and it is actually fascinating! I do agree though, that it can be taught in an uninspiring manner and can be experienced as a lifeless leftover of the real thing.
Interestingly, people who have played for a while without any understanding of the "makings of" feel the need for music theory at some point. They feel how the lack of this knowledge is holding them back from moving on with their playing.
If music is a language, theory is the grammar. Children learn their mother tongue instinctively during their first years of life. Later on, at school, they learn the laws behind the familiar language and with that background they can use the language on a higher level. The knowledge of grammar enables them to deepen their understanding of more complex texts. It also enables them to become confident, articulate and creative.
Music is also a language in some sense. Our first experiences in music are instinctive. We can sing and even play an instrument up to a certain level without understanding the laws behind it. But if we stay on that instinctive level we are restricting ourselves to the basics. By learning the secrets of music theory we emerge out of the blindfolded status and become aware of the tools the composers were using. When we have more understanding of what the composers were doing and how they created certain effects, we can be more in sync with the composers and our interpretation will be enriched and deepened. Understanding music theory is also the key to composing and improvising. If you are familiar with the materials at your disposal, you can create a lot more effectively than if you just follow your instincts.
Music theory is supportive to music making if viewed as an organic part of the living music. The problem starts when music theory branches off into a separate existence. When students write down notes in the "right " place without knowing what that will sound like, there is little value to their work. To do music theory without linking it to the actual context of sound is like learning the theory of swimming without ever getting wet. Unfortunately, this is done quite often so it is not surprising that music theory is so unpopular with piano students.
My favorite Theory books are the ones from the Trinity college series. These workbooks have a very systematic and gradual build up, with clear and very understandable explanations. I highly recommend you actually play all the exercises after writing them down. Aim at hearing the written notes inwardly before playing them and then listen to them carefully, so that the borderline between music theory and music practice will disappear.
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