Chord progression in F but with a stray B note

Question

Longtime lazy play-by-ear guitarist, now working on learning theory (and if it matters, mainly focusing on the ukulele now)

I was fiddling around the other night and came up with a progression that I'm in love with: C - G - Bb add9 - F

I wrote it in my notes and thought I had it figured out as being in the key of F and being a V - II - IV - I progression. Maybe some or all of that is accurate, but then I noticed that there's a stray B note in the G chord that doesn't fit in the F major scale. Changing the G to Gm doesn't sound good, so there's something about this that's working. I looked at some other questions and I think the answer has something to do with G being the dominant of C (if I understand correctly). Either way, how should I think about the key and structure of this progression? What concepts can I look further into to be able to do this kind of thing on purpose?

Answer 1

We have sooo many questions asking about 'foreign' notes (non-diatonic). There's not a thing that says all notes in a song need/must belong to a certain key. Were that the case, 90% of songs would be out of order!

By listening to where in your sequence the song could stop, be at rest, or evevn finish, that will be a great clue as to its key. However, whichever chord that is, with those chords, there's going to be a 'stray' note somewhere!

C, G B♭ or F? Maybe; or maybe even a different key.

Key C means the B♭ is the 'odd one out'. But can be (is) attributed to being from the parallel key of Cm. All well and good.

Key G means the B♭ and F are both out of key. Again, both come from the parallel Gm.

Key B♭ means G and C are out. C is V/V, and G is V/V/V. A little far out, but certainly not uncommon.

Key F means G is the odd one, but easily explained by V/V.

So it's all good - and your sequence, in any of those keys, can be found in a myriad of songs over many decade, if not centuries!

Learning theory will be greatly enhanced by following this erudite site, with many, many theory questions and great answers.

Answer 2

To figure out the tonic, identify the point of "coming home" - usually at the very end of the tune, and see what tone and chord you have there. By your description, F seems most likely here; another candidate might be C, and other keys aren't strictly impossible either. The information that's missing to conclusively confirm it's in F is where that coming-home point is.

G in the key of F is kind of common (and so is Bb in the key of C). You're right that it's got to do with being the dominant of the dominant (or the subdominant of the subdominant). In this way, the chord is related to the key, and that makes it a somewhat likely choice.

Please don't fall victim to the misconception that all notes in a piece should belong to the scale; it happens very often that a few here or there don't. There's no taboo.

I wouldn't know about theoretical concepts; to do this kind of thing on purpose, I'd suggest you just get yourself familiar with a lot of songs and look at the progressions they use. At least that's how I do it.

Answer 3

The "B" note is not at all wrong or complex. The chord progression you mentioned is valid.

Usually, the II is minor. You have used it as major. These things are fine. You can also use the IV minor chord in any major key. It is beautiful but doesn't follow the typical music theory rules we all learn.

I would say you are correct to document it; but don't overthink it. Transpose to another key and see if you still enjoy the sound. If you do, you made a great discovery that you can use in your own music.

Answer 4

The chord progression C-G-B♭-F is a common one and is usually heard as in the key of C. The key features are:

(1) Use of triads that have at least some notes in common with the main key; (2) A smooth chromatic line in one part: c → b → b♭ → a are notes in the respective chords.

The addition of the 9th in one or more of these chords adds color without changing the function. Here, the B♭add9 is attractive in giving a quasi pedal point (the tone C is common to all but the G chord).

Another progression that may be compared is that of "Hotel California": Bm F♯ A E G D Em F♯. Here the first 6 chords include a chromatic line descending from the tonic, b.