I've just written a piece by ear. The chord prog in the verses goes Cmaj7, Bm7, Amaj7, (let A ring for two bars). Now I know that traditionally sticking to the rules the Amaj should be a minor, so I guess this is a borrowed chord. Im having a hard time wrapping my head around why this sounds good and what I can refer to my borrowed chord as, does it come from a relative or parallel scale? And if so, which?

closed as off-topic by jjmusicnotes, Dom Oct 12 '17 at 15:56

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Key depends on so much on what notes you use but how you use them, e.g. where in the piece there is a sense of rest or arrival. So we'd be able to give you a better answer if you gave us more information or provided a link to a recording.

With no other information, I'd guess that the piece is in the key of A major, since it lingers on the A chord and it's a maj7 (which can only appear as I or IV in a major key). Under that theory, the C chord would be borrowed from the parallel minor as a iii chord, and the B could be sort of an inversion of a D6 chord acting as a weak dominant chord.

  • Would Cmaj7 be III rather than iii as a parallel key chord? In A major, Bm7 stands on its own as ii7. – Tim Oct 11 '17 at 10:08

The key is not of any modes, since no modal sequence contains maj, min, maj. This means that no one key fits those chords. Which leaves use with two possible options.

  1. They key is modulating between different keys, this is fairly common in music. Eg. It could be modulating between EMaj and Emin. In a practical sense this key has no name!

  2. But if I were to put a key on this progression, in a technical sense the key is in A major. Even though the CMaj7 isn't in an AMaj, doesn't mean the song's key isn't in major due to Modal Interchange. Modal interchange uses the borrowing of chords from any parallel mode that still fulfil required details for an AMaj key. Only some interchanges will work and to determine that is up to your ear. Example of interchanged used:

    Parallel Modes:
    AMaj: AM, Bm, C# | AMin: Am, bdim, CM

    Interchanged mode mode:
    A: AM, Bm, CM

It's like lego, just take the chords that you need/make up your song. The 1 (AMaj) and 2 (Bm) from A Major and borrow the 3 (CMaj) from A minor. Think of it as sprinkling a touch of A Aeolian over the A Major for a little more flavor. One may ask, if both modes are used, than wouldn't they key just be A, not A Major? Technically the key is still A Major because of 3 things:

  1. Theoretically, we resolve to an A Major, therefore the key is A major.

  2. Practically, the chords imply a major sound.

  3. Logically, there are more chords used from A major than A minor.

Overall, what you've done is found a real life music theory glitch, there are only misty guides and shadows within the theoretical world when getting into this non-theoretical playing. The only guide is your intuitiveness and your ears...you determine what chords you can borrow when and where by listening, that's the only way.

  • Thank you, that makes sense now. However I just have one question. When it comes to writing the bassline, how should I go by approaching this? – Marwan Farha Oct 11 '17 at 8:07
  • 1
    You could approach it with chord/scale relationship. Play C Major of the Cmaj7, B Minor of Bm and then A Major over Amaj7 – r lo Oct 11 '17 at 16:19
  • @MarwanFarha the best way to approach the baselines to stuff like this is to be independent of scales. Use you're arpeggios that are relative to what you're play because they contain the 'allowed notes.' If you like this answer click the tick next to it ;) – jazzboy Oct 11 '17 at 23:49
  • What difference between A and Amaj, or it is the same? – nick_n_a Nov 28 '18 at 15:25

You have chosen three chords that do not all use notes from one scale. That is absolutely fine. There is no rule that says they should. Yes, if the piece used only the notes from C major, the A chord would be A minor. But it doesn't, and I say again, that's just fine! It seems the music finds a resting place on the Amaj7 chord. You might find it useful to analyse the chords as bIIImaj7, ii7, Imaj7. You might not. What does the melody do?

I imagine the bass line will basically go C, B, A.

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