I've been working on one of my own songs and trying to understand why some of the things I wrote by ear sound good to me. I initially thought part of it might be B♭ Dorian, until I realized my home chord is B♭ major. Comparing the two led me to B♭ Mixolydian, and suddenly several things made sense, especially an A♭ melody note I play over an inversion of B♭. That's the ♭7, one of the notes that gives Mixolydian its sound. Something else that's helping me have these little light-bulb moments is that I've been learning (in a fashion) my way around a keyboard. I'm a guitar player, so I've always tended to visualize theory through the fretboard. But on a keyboard, the relationships are laid out differently. I'm finding that I can see intervals, chord tones and changes to a scale in a way that sometimes isn't immediately obvious to me on guitar. For example, comparing Dorian and Mixolydian from the same root on the keyboard made something jump out at me: they're identical except for the 3rd. Dorian has the ♭3 and Mixolydian has the major 3rd. Suddenly the difference between that minor and major home chord wasn't just something to memorize; I could see what had changed. Then I looked at another chord I use in the song: G diminished (G–B♭–D♭). That's not diatonic to B♭ Mixolydian. The diatonic chord built on G would be G minor. Now, I could have looked at that and thought, “Well, I'm doing it wrong.” But I'm not. I like how it sounds. And I think that's another little theory light-bulb moment for me. Music theory isn't a rule book telling you what you're allowed to play. It's a guide that can help you understand what you're already hearing and invite you to search for other ways to accomplish your musical goals. Instead of theory telling me, “You can't use that chord,” it gives me a much more interesting question: “That chord doesn't come from where you thought it did. So why does it work?” And now I want to find out.