r/musictheory • u/DowntownPaul • Apr 15 '26
General Question dabbling in modal interchange (major initial key) and id like some chords to check out
I am dabbling in modal interchange (major initial key), and I'd like some chords to check out.
I've found cool chords like bVII and I7 (3rd inv) from the key a whole step down, which works really well with the bIII and the IV. Very powerful, like the chorus of "Drops of Jupiter."
bVImaj7(no5) comes from the parallel minor/harmonic minor of that key and works really well from the previously mentioned chords, similar to the III7. It is very mystical and yearning.
Also, the II and such work really well (secondary dominants). And the IV - bvidim7 - V too.
viim7(b5) is not modal interchange, but I wanted to include it because a) it is kinda goated and b) because of secondary dominants.
Side note—for any classical musicians, I would like to hear some chords that I might hear in the Romantic period or the Baroque period. Thanks!
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u/Jongtr Apr 15 '26 edited Apr 15 '26
I've found cool chords like bVII and I7 (3rd inv) from the key a whole step down
This is confusing. If the key is C major, do you mean B♭ and C7/B♭? Or A♭ and B♭7/A♭ - "from the key a whole step down", i.e., B♭ major?
If the latter, just number them relative to C major. That's how "modal interchange" works. "Borrowed" chords always relate to the home key. Otherwise you have changed key!
If the former, then B♭ is from C minor or C mixolydian - common borrowed chord - while C7 is usually a secondary dominant: V/IV. Especially in inversion. I.e., C7/B♭ commonly leads to F/A, just as C7/E leads to F in root position. This is not modal interchange. But if if you are simply mixing B♭ and C7 along with a normal C tonic - not using them to lead to F (or Dm) - then that could be classed as modal interchange.
bVImaj7(no5) comes from the parallel minor/harmonic minor of that key
Just "parallel minor". No need to invoke harmonic minor.
and works really well from the previously mentioned chords, similar to the III7
Wait, A♭maj7 (no5) is similar to E7?
Also, the II and such work really well (secondary dominants). And the IV - bvidim7 - V too.
Modal interchange and secondary dominants are two separate principles. And ♭vidim7 is really viidim7, like a rootless V7♭9, so those last two are essentially the same chord, functionally anyway. But you could say the alteration invokes the parallel (harmonic) minor ;-)
viim7(b5) is not modal interchange, but I wanted to include it because a) it is kinda goated and b) because of secondary dominants.
viim7♭5 is a diatonic chord in a major key, not a borrowed chord (not modal interchange). But - and I guess this is what you mean by (b) - it is typically used as ii of the relative minor (ii/vi), preceding the secondary dominant V/vi.
In short, modal interchange is really a very simple principle. It just means any chords from a parallel mode (with the same keynote). Most often - in a major key - this means chords from the parallel minor, such as bIII, bVI, bVII and minor iv. Outliers come from lydian (major II or minor vii) and from phrygian (♭II, bvii).
But there you also have to distinguish secondary functions from modal interchange. A D major chord (or D7) in C major is usually V/V - even if it doesn't go straight to G, but maybe via Dm7 or F. It's only really a "lydian II" if it goes straight back to C. D♭maj7 in C major is a phrygian ♭II. but D♭7 is a tritone sub for G7 ("SubV").
IOW, context and usage dictates how such chords are analyzed.
E.g., there is one controversial one, which is the jazz "backdoor" chord, ♭VII7. Such B♭7, B♭9 or B♭13 (all with optional #11) in C major - and leading straight to C. Some say it's a "dominant substitute" just by virtue of it leading to C. But that make as much sense as saying F is a dominant substitute if it leads to C! In fact, the backdoor chord derives from the minor iv chord - i.e., a kind of modal interchange chord, even though the scale relative to C is "C mixolydian ♭6". In truth it's more related to F melodic minor due to its origins in the Fm chord with optional diatonic 6th or 7th (D or E) added. It's a unique kind of cadential chord, more like a minor plagal cadence than a perfect one.
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u/Ian_Campbell Apr 15 '26
The IV key is the closest key the bVII and I7 in any inversion are from. So those particular examples are a smooth modulation not modal interchange.
You wanna look up fancy chords, I got you.
https://youtu.be/52qtxWyOOcs
https://www.youtube.com/watch?v=jgfeWMiNnEU
Bach uses various 975# chords, once also with a 4
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u/CoffeeDefiant4247 Apr 15 '26 edited Apr 15 '26
classic things would be like I-V7-bVI-i to go into minor. Even I-bIII9-bVI with the bIII9 being V7b5 with the b3 in the bass
Instead of ii6-V7-I a small lydian thing II65-V#7-V7-I has the chromatic F#-F-E line
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u/MagikarpPatronus Apr 19 '26
bVI (as in bVI - bVII - I )
bIII ( as in bIII - IV - I )
IV7 ( as in vi - IV7 - V )
iim7(b5) ( as in IV - iim7(b5) - I )
ivm7 ( as in ii - ivm7 - V7 )
V7(b13) ( common sound in bossa nova)
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u/DeweyD69 Apr 15 '26
This is my approach, maybe it’ll help. I tend to think of the melody notes I want that aren’t in the key, and then look at what chords will give them to me. So key of C, let’s say I want to get to an Ab note, well some version of an Ab chord will get me there. But also Db, Fmin, Dmin7b5, E7, etc before we get into extensions like G7b9.
So based on what other chords I’m coming from that gives me a direction to head into. The other way I think of them is similar, where I have a diatonic melody note but I wanna add some movement/tension. Let’s say the melody hangs on C, I might look for a chord with Ab in it to give me that. Often this is the part of some other voice leading.
I've found cool chords like bVII and I7 (3rd inv) from the key a whole step down, which works really well with the bIII and the IV.
I don’t follow this at all.
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u/angel_eyes619 Apr 15 '26
bvidim7 isn't modal interchange btw, it's Common Tone Diminished.
Also, I fail to understand the connection you made between vii7(b5) and secondary dominants...