What Is Music Theory?

music theory is the study of how music sounds.
music notation itself is not music theory, although music notation is relevant to how we can communicate about music.
music theory is often presented as a set of rules.
rules in music theory are not like laws that tell you what you must or cannot do.
rules in music theory are like the law of gravity that tell you how the world works - they predict cause and effect.
so, "if you want to achieve a particular sound, this is how to achieve it."
your ear can help you find the sounds you want, but understanding theory can often get you there faster.
studying theory can expose you to interesting new sounds you didn't even knew you might want.