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I was reading a theory book and it's talking about "Modal Interchange." The key is in C Major and I can't understand how BbM7 went to CM7. Isn't BbM7 a secondary triad Sub Dominant? And as I know, a secondary triad Sub Dominant can't just skip to the Primary triad Tonic.. So what is happening here?

  • Can you please edit your title to ask the question. It is not helpful to just have "modal interchange chord." Thanks.
    – Doktor Mayhem
    Commented Mar 25, 2018 at 12:16
  • @DrMayhem Sorry about that ! I fixed it ! Commented Mar 25, 2018 at 13:23
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    What theory book is this?
    – Richard
    Commented Mar 25, 2018 at 15:55
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    Thanks Hyun - much easier to find in a search now!
    – Doktor Mayhem
    Commented Mar 25, 2018 at 16:37

2 Answers 2


What's this idea that one chord CAN'T skip to another? Bbmaj7 demonstrably CAN go straight to Cmaj7. Do you like the sound? Good. Add it to your bag of musical resources. If you subscribe to some system of 'theory' that says it can't be done, find a better sysyem of theory!

Theory describes. It does not give permission.

I'm going to keep saying this until it sinks in! Seems to be taking a long time :-)

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    Yes I believe theory could be bended. But even those cases it has some reasons why that works and sounds fine. Commented Mar 25, 2018 at 15:08
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    There may be deep conceptual reasons why one musical event sounds better than another. But the 'reasons' we are usually given more often justify something merely on the grounds that it's been noticed and categorised. There are systems of categorisation based on functional harmony. But they are not exclusive. 'It's next door' is also a perfectly good excuse for moving to a chord!
    – Laurence
    Commented Mar 25, 2018 at 15:58
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    @HyunYooPark - who states that Dm7 can't go straight to C maj? Lots of music does exactly that, so this guy must have lived under a stone for a while. As Laurence says about 'theory'. That's just what it is. If everyone stuck to 'the rules', we'd all still be singing some pretty boring stuff!
    – Tim
    Commented Mar 25, 2018 at 16:07
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    Laurence, I know sometimes I give you a bit of a hard time for being brutally direct, but you are absolutely on the money with that middle paragraph.
    – Doktor Mayhem
    Commented Mar 25, 2018 at 16:39
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    @DrMayhem - too true! It seems that there are more and more questions such as these. No-one's listening to Laurence!
    – Tim
    Commented Mar 26, 2018 at 6:55

i 'm studing a theory book that talk about the bVIIM7 function.These chords are non diatonic chords inherited from the Myxolidian mode.Their function us a SUB-DOMINANT function. For instance in G Major you can find an FM7 because in G mixolydian the F is not #, as in a G7 chord. The bVIIM7 chords tend to resolve on I. But as a sub-dominant chord, you can find it in a IV-V-I cadence where the bVIIM7 take place of the IV. This the case in the pop song i'm studying where FM7 (bVIIM7) is preceded by a C (IV) and followed a D7 (V7) and a G (I). This emphasizes its a SUB-DOMINANT function ( I Need you by America - 1971) Cheers !

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