From “The Essential Secrets of Songwriting” website:
Most of you know that I have had an internet presence on the web for years as the author of “Gary Ewer’s Easy Music Theory.” And you know that I am a big fan of any and all musicians learning some basic music theory. But maybe not for the reasons that you think.
Occasionally someone will write me to ask a question about a song they’re writing. And the question is usually something like, “Is it OK for me to have this chord follow that one…”, or “Can I write this note in my melody if I use that chord…” The answer is: If you like it, then use it!
Music theory was never intended to tell you what to write! Music theory can expand your creative abilities, and can help you communicate musical ideas, but it was never intended to make compositional decisions for you. If that were the case, no evolution in musical style would ever be possible, because we’d all be too busy following the rules.
Good composition does NOT come from theory. In fact, it’s the other way around. Music theory is basically a study of music history, in which we look at what composers have written, and come up with a “theory” for why it works.
Having said that, a good understanding of the basics of music theory can tell you why certain musical elements work the way they do. It allows you to understand, when you hear a neat chord or a great musical moment, exactly what’s going on that makes it great. And because you have the theoretical knowledge to understand it, you can replicate it in your own way in your own songs.
If you don’t know how to read music, I recommend that you start learning. I think you’ll find that your imagination will become disciplined and focused in such a way as to help you start to create even better songs.
-Gary Ewer
“The Essential Secrets of Songwriting”