As a species, we were playing music long before we were developing and learning about music theory. So, it is not required that you learn music theory in order to master an instrument. But learning music theory can deepen your appreciate for you music, and inspire you and help you to compose music as well. Music theory describes a set of rules about how different sounds do and don’t go together. While in fact, theory goes deeper than this, and can be a lot more complicated that this, this is fundamentally what it comes down to. So, if you want to learn an instrument without it, you can. However, if you want to explore what music is really all about and how it works, music theory will help you.