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In jazz there are many chord substitutions with various names like tritone, but there's a particular chord movement which I have seen in many jazz standards where major7 is immediately followed by a minor7 of the same root. For instance in a popular jazz standard Misty there's a part where Abmaj7 is immediately followed by Abm7.

Is there a theoretical explanation to this type of change and when should it be applied?

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    Check out this page. You've identified this major-to-minor movement within an extremely common chord progression sometimes called the "backdoor progression." It is all over the place in jazz (Misty, How Deep is the Ocean, My Romance, Stella by Starlight, Just Friends...). The major-to-minor comes in when you backcycle (add V's and ii's to the V's). For example, check out the movement around the circle of 4ths: || EbM | Cm | Fm | Bb7 || Bbm | Eb7 | AbM | Abm Db7 || EbM | ... – jdjazz Apr 6 at 22:38
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    @jdjazz your response should be posted as an answer more than a comment. Kindly expand it and post it as an answer. – Phemelo Khetho Apr 7 at 16:30
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    There are a lot of good answers already, and if I were to write a full answer, it would be way too similar to Matt L.'s (who is spot-on, I think). I wanted to include a comment mostly to share the linked article and to provide some context for understanding your question and the answers below. My point about the circle of 4th's isn't an answer to your question--the answer (I think) is Matt L.'s explanation about borrowed chords. I just wanted to highlight the circle of 4th's as something to keep an eye on when looking at the existing answers and thinking about why the progression sounds good. – jdjazz Apr 7 at 21:49
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    @jdjazz thanks for the explanation. As for which response is spot on, I will rather wait until I have heard other possible answers. For instance the comment and the link that you gave provided a much simpler and detailed explanations of the "Backdoor Progression" which is a concept that I wasn't even aware of and none of the answers given here had touched upon. – Phemelo Khetho Apr 7 at 22:36
  • Those are good points. So, the reason I prefer Matt L.'s answer is that it explains why | AbMaj | Abmin | EbMaj | works as well as | AbMaj | Abmin Db7 | EbMaj |. I see his answer as being somewhat more general, whereas the backdoor progression is maybe a narrower idea. The article does a great job of explaining the resolution, but it focuses on the V7 up a whole step to I resolution (e.g., Db7-EbMaj), which is a little different from the major-to-minor movement you've identified in this question. – jdjazz Apr 8 at 0:53
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This happens very often in a major key with the IV chord, which is altered to the minor chord with the same root (iv), and then resolves to the tonic chord. This works so well because of the voice leading. E.g., in C major you would get F to Fm to C, where the note A (third of F) moves down to the Ab (third of Fm) resolving to G (fifth of C).

The iv chord in a major key is often called a borrowed chord, because it can be viewed as borrowed from the parallel minor key (i.e., the minor key with the same root). This borrowing is part of a broader concept called modal interchange.

In the song Misty, if played in Eb major, the Ab maj7 chord is the IV chord, and the resolution back to Eb maj7 is as described above, just that there's usually a Db7 (bVII) chord in between the Abm7 and the tonic chord. That Db7 has the same function as the iv chord, because it is basically the same as an Abm6 chord, just with a different root.

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  • Yes, the ⅳ chord has also been discussed in numerous other questions on the site. IMO it acts not so much as a burrowed chord from the parallel minor, but as a neat way of bringing in some tension in form of notes from the strongly dominant ⅶ⁰ chord, without the dissonance of an actual diminished chord. – leftaroundabout Apr 4 at 16:33
  • This answer is by far the best explanation. Using chords from the parallel minor key is a very common and effective device. It occurs in many other ways, not just on a IV chord, for example on the tonic in several Jobim tunes like Wave and Triste. Other widely used parallel minor chords are the bIII and the bVI. Also I don’t see any correlation between a IVm7 and a VIIo chord. – John Belzaguy Apr 4 at 17:04
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This is not a chord substitution but could be a cadence or a key change. As mentioned in other answers a very common device (found in other forms of music not just Jazz) is

IV --> iv --> I (example in the key of C, F --> F min --> C)

The Maj 3rd of the IV chord is the 6th degree of the Key and the movement is chromatic walking down to the 5th degree of the key, the 5th of the I chord.

This is an alternate resolution to the classic IV --> V7 --> I.

If one is changing key down a whole step then this could be a set up for a ii-V-I in the new key. Changing from C to Bb one might have C --> C min7 --> F7 --> Bb.

Moving away from your example for a moment it is quite common to replace any chord in the circle progression with its dom 7th to move to the next chord in the progression (with the exception of the IV as that moves to the viii).

C --> C7 --> F --> F# dim --> B-7(b5) --> B7 --> E-7 --> E7 --> A-7 --> A7 --> etc

This created the sound and feel of a resolution to the next chord in the sequence.

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    +1 I not only agree in principle, but I'd go as far as to say that this is exactly how the "trick" is used in the vast majority of the cases. Tune Up by Miles Davis is a classic example of just that. – MMazzon Apr 6 at 15:18
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This isn’t something that theory ‘commands’ you to do, in the way that a dominant expects to resolve to a tonic. It's not following some rule. It’s just a thing you CAN do, and not a particularly ‘outside’ one. Same root, different flavour of chord. A unifying factor and a variation. Happens all the time in music. Repetition, imitation, variation.

'Misty' is based on two types of stock progression. There's the ii7 - V7 - I in bars 2-3 then again (aiming for a different temporary tonic but not actually getting there!) in bar 4. Then there's the standard 'cycle of 5ths' turnaround in 5-6 and 7-8.

ii7 - V7 - I is a very strong progression. You can jump to almost ANY m7 chord with the flimsiest of excuses and justify doing so by treating it as the beginning of such a progression. Modifying an existing chord is a pretty conservative way of setting off for somewhere exotic. 'Giant Steps' uses a rather more contrived method!

In the case of 'Misty' I can't see much point in calling it anything more complicated than 'modifying a chord'. Does 'Modal Interchange' tell you anything extra?

enter image description here

Here's another direction 'Misty' could have taken. Still ii7 - V7 - I, which is what gives it integrity with what's before. (I've carried on and 'taken it back home' but I didn't have to.) Not quite so obvious, which makes it... well what? 'Theory' can tell us it's a less obvious choice, but not that it's a worse one. (Since when was 'obvious' better?)

enter image description here

(And I'm sure you've noticed that 'Misty' DOES take very much this route in the middle 8!)

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    I didn't downvote your answer but if I understand your argument correctly, then you're saying that the Abm7-Db7 combination might as well have been any other II-V progression. This is really not the case, and there's a good reason that it is Abm7-Db7, and not (for instance) Am7-D7. – Matt L. Apr 4 at 17:06
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    I didn't downvote, but there's a chance for an interesting discussion. "Does 'Modal Interchange' tell you anything extra?" Yes. When that Abm7 chord kicks in, to my ears, self-evidently the D note becomes Db automatically, even if the next chord wasn't a Db7. "Modal interchange" is a more suitable word for describing the change of situation than just saying that one single chord was modified. I mean, nobody would try to solo a strong D natural on the Abm7 chord? – piiperi Reinstate Monica Apr 4 at 20:27
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    Well, like so many musical things it IS just an artistic decision! Theory can describe it, but theory doesn't command or predict it. It COULD have been Am7 - D7. A bit more 'outside', but quite possible. It would have led to a temporary tonic of G or Gm. See my extended answer above. – Laurence Payne Apr 5 at 1:13
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    Yes, "modal interchange" does tell us something extra, because it tells us a specific detail of this style. If someone were to come along and try to write something in the style of "Misty," modal interchange may get them there, and just "modifying a chord" likely won't. Imagine you sat down in a writing class and the instructor said "Eh, grammar is just theory. Just put whatever letters you like right next to each other...it's your artistic decision!" That's hardly an answer, don't you think? – Richard Apr 5 at 14:45
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    @LaurencePayne Modal interchange is a very specific subset of modifying a chord. Which is why this clarity is important: just saying "modifying a chord" opens up possibilities far beyond the realm of mode mixture. – Richard Apr 6 at 12:02
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One place I've seen this done a lot in jazz harmony is in a pair of descending ii-V progressions (often in the bridge). As an example, E♭m7 A♭7 D♭maj7 D♭m7 G♭7 C♭maj7. There's a lot of ways to explain why this 'works', but the key is that the shift is primarily created to get from the first key, D♭ major, to the second, C♭ major. You could also call the whole progression a variation on iii VI ii V I in C♭ major.

The color shift one gets from that parallel transformation is a nice sound, and just as good a reason to use this chord sequence as any other. So most of the time I see that chord movement of major to minor on the same root, it's either the minor plagal sound (IV iv I), or it's the ii V down two semitones thing I explained above.

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I think one of the classic sources for the sound is the B section of Cherokee..

C#m7  F#7   BΔ7   BΔ7
Bm7   E7    AΔ7   AΔ7
Am7   D7    GΔ7   GΔ7
Gm7   C7    Cm7   F7

Each of the four bar lines is a basic ii V I pattern, but it is sequenced down a full step four times.

The transition between each sequence is where the major to minor change happens. Like: ...BΔ7 | Bm7...

On a structural level you could say that major to minor change is just a happy accident and the bigger picture idea is ii V I sequenced down by whole step. That's a theoretical explanation for the major to minor change in what is otherwise just a long progression by descending fifths from C# to F.

This song is supposed to be the one that Charlie Parker woodshedded on to develop his chops, so it seems like an important example to mention, and it happens this way in other songs.

Another common example is using a borrowed chord, a chord that comes from the parallel minor key. In I V IV iv | I the minor iv is "borrowed" from the parallel minor. In that case the theory is the borrowed chord maintains its function. So, both major IV and minor iv "function" as subdominants and the change of major to minor just adds chromatic color.

I put borrowed and function in quotes above, because some may prefer to explain the motion as a chromatic passing tone between the sixth and fifth scales degrees. I think that is a fine explanation too, and doesn't contradict the idea there is not a change of function.

Misty has this kind of "borrowed" progression, but it uses it in a specific way involving a bVII chord which has it's own special name: the backdoor progression: iv bVII I.

Compare the Misty borrowed chord explanation to the Cherokee sequential explanation. While the "function" of the two chords is the same in Misty in Cherokee the function changes. In Cherokee when getting to the BΔ7 the chord is a temporary tonic I in the pattern ii V I in C#m7 F#7 BΔ7, but then when it changes to Bm7 in the next sequence it becomes the supertonic chord ii of ii V I in Bm7 E7 AΔ7. In that case the two B chord not only change from major to minor but the function also changes.

If all this dithering about the use of "function" is a problem, you can look at it more plainly. In Misty when you look at the larger picture the opening section is an elaboration of movement between Eb and Bb (clearly I and V.) It starts on Eb and ends on Eb, that's the tonic. Regardless of the terminology used to describe the two major and minor Ab chords, one thing is clear: they aren't doing anything that changes the tonic of Eb. That's an "A" section establishing a tonic. The "B" section of Cherokee it totally different. It starts on C# and ends on F. It keeps moving and moving, transitioning back to Bb. It's a bridge returning to a tonic. Instead of talking about function we can describe them as two very different structural events.

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The Abm7 chord is just doing the old jazz harmony trick, a temporary change between parallel minor and major tonalities. It can also be called a tonic shift of three semitones. Matt L. already gave an introduction to the subject of modal interchange, but to give a different perspective, I'll add a demonstration of what I feel the Abm7 chord is doing:

I think Laurence tries to say that if we take the question literally, the only "theoretical" explanation for why that was used must come from social sciences or psychology or something. Music theory can only describe the phenomena that happen in the harmonic context AFTER someone has decided to want to do that change. Why they did it - it was an artistic choice. They liked the feelings produced by the change, or at least they thought that prospective customers might like it. ;)

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