The first reason you’ll need music theory is to make you a better musician and songwriter. I’m not saying you can’t be a good musician and songwriter without music theory, but it really helps. It gives you a foundation upon which to stand.
For example, if you’re writing a guitar solo for one of your songs, it’s going to be much easier if you know the scales and where you can play things on different parts of the guitar. You won’t have to guess until you find the notes you want.
This takes us to another way music theory can help: it allows you to do things on purpose instead of just stumbling into them. Now, sometimes some of your best work will come after you’ve stumbled into something. But knowing music theory makes it easier to make better music intentionally.
Having a head knowledge of music will also allow you to better understand other artists’ songs, especially if those artists used music theory to create the songs. You’ll understand why they chose the seemingly random chord progression or how they came up with such intricate melodies and harmonies. Your appreciation for and understanding of music will grow.
Better understanding the theory behind songs helps you understand why they make you feel a certain way. A great song makes you feel things, we all know that. With music theory, you can see why certain notes and chords put together make you feel those things.
And once you understand the why and how of music, it can seriously help you move past writer’s block. If you know in your head what notes in a scale will work over a chord progression, the music will come more easily. If you’ve ever had trouble figuring out what chords you can play next or if you’ve struggled to come up with a melody, music theory can help you find your way.