Below are my result, with a bit of color-coding to make make things clearer.
So what does it all mean? Well, here are some guidelines for starters:
- Keys on the left-hand side, with logical chords in that row.
- Functions are written across the top row, with corresponding chords in the columns.
- Light gray chords are unique to major; dark gray to natural minor. But that doesn't have to stop you from borrowing chords from the other mode.
- In general, for those of you who didn't know, chord progressions tend to follow a pattern of tonic - ... - dominant - tonic, with other chords interspersed. "Predominant" chords can prepare a dominant chord, and others can precede a predominant.
- Pay attention to the indicated color, which generally match the name of the function. Some intermediary chords have a different color, and that's because depending on their usage, they fall under either category (to the left or right).
- In general, chords within the same category can be substituted with another, regardless of accidentals (chord alteration from the norm).
- That slash notation (i.e. X/Y) are secondary dominants, noted for convenience. What that means is that the indicated chord (call it "Z") functions as a dominant "X" of (i.e. prepares or expects) the chord "Y". So if you used that "Z" chord, the next chord you expect is "Y". But as I mentioned in that last point, instead of "Y" you could use another chord in Y's category.
- Seventh chords weren't considered, but generally they serve the function of the triad on which you're stacking that seventh.
- The chords "vi" and "bVI" are orange (not yellow) because they can be substituted for the tonic on occasion in what's referred to as a "deceptive cadence".
- Just because a chord has funky symbols like flat signs or slashes, doesn't mean you should shy away from it. They actually sound pretty cool and can really add flavor to your music.
- Common practice / classical theory is a bit more rigid than contemporary music (primarily using only the notes within the key with subtle alterations). I think this chart helps show how "foreign" chords (i.e. beyond the key) connect to other chords.
- I didn't realize that the "bII" chord can also be a dominant ("tritone substitution"). Usually it appears in first inversion (i.e. with the third in the bass) as the "neapolitan".
- The "bVII" isn't used much functionally in old-school music theory, but I've heard enough examples of it as a dominant. Oh, and speaking of the dominant, just because something's called a dominant doesn't mean it has to be the penultimate chord. Have a ball.
- I tried to figure out a way to fit "bV" (or any chord built on the tritone), but I couldn't find it. I also wasn't sure where to fit the minor "v", but I guess it would be a dominant.