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A comment discussion under this question from me, clued me in to the fact that I don't really understand how minor keys work very well. So here is what I think I know

The natural minor comes from the Aeolian mode of the major scale. It gives us the following triads for use in harmony:

i ii° III iv v VI VII

From what I have been told, classical minor harmony also utilizes the harmonic minor. which is the same scale with a sharpened 7th. This implies the following triads (notated with respect to the degrees of the natural minor):

i ii° III+ iv V VI #vii°

Now the comment "the 6th and the 7th scale degrees can be modified whenever the composer feels it's necessary to do so." leads me to believe that this is not an all or nothing thing, and I can more or less mix and match to suit the sound I am looking for. First of all, am I right up to this point? Should I tend to favor the triads from the harmonic minor?

Taking this further, I could imagine different combinations of sharpening or flattening the 6th and 7th scale degrees. Well there would only be 3 other choices really: Melodic minor, a #6, or a #6 with a b7. These will each imply different triads. Are any of these (besides melodic minor) going to be harmonically useful? Can I effectively use any of the resulting triads in a progression and not sound out of key? I realize this may be subjective to a certain degree.

To throw another wrench into the gears, how do other "minor" modes play into this? I am considering a scale mode to be "minor" if its 3rd is a minor third and the 5th is a perfect fifth. For example, in the dorian mode: Can I play the same tricks with the 6th and 7th there too? Or will I run into problems?

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This is music. You can do whatever you want. :) –  Kevin Mar 20 at 12:40
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Slightly off-topic but might be interesting there is also a major-minor scale; it's like the major scale but with a lower 6th. A really nice, bitter-sweet effect. –  Roland Bouman Mar 20 at 13:16
    
@Kevin I second that. I would put it like this: when playing in a minor key, it's common to borrow notes from the major scale of the same root note. Thus in A minor, you may want to throw in G#, F# and possibly C# in addition to tha natural notes. –  steve verrill Mar 20 at 13:17
    
@RolandBouman oh that sounds neat. Sort of starts major and ends minor. –  Tim Seguine Mar 20 at 13:18
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Another possibility for the major third would be to use it as a pivot chord to modulate to the (minor or major) key one fourth above; For example, Am Dm E7 A | Dm G C F | Bb E7 Am (Hello by Lionel Richie). To make the modulation work even better one would use A7 instead of just A. –  Roland Bouman Mar 20 at 13:23

3 Answers 3

This is an excellent and important question. In a minor key, all 4 possible combinations of 6th and 7th scale degree are used, and each combination corresponds to a scale:

  • b6, b7: natural minor (aeolian)
  • b6, 7: harmonic minor (creates a dominant V chord with a leading tone to the root of the key, so it was 'invented' for harmonic reasons)
  • 6, 7: melodic minor (removes the augmented second interval between b6 and 7 of harmonic minor, so it was 'invented' for melodic reasons)
  • 6, b7: dorian

All chords from these three scales can be and are used in compositions in a minor key. They can (and again are) rather freely mixed by composers in one and the same piece. It is a big misunderstanding by beginners that pieces are written 'in melodic minor' or in 'harmonic minor'. Usually a piece is just in minor and all combinations of 6th and 7th scale degrees are used harmonically and melodically.

The truth of my quote "the 6th and the 7th scale degrees can be modified whenever the composer feels it's necessary to do so" was doubted in another answer. However, it is almost a tautology because there are no rules and if there were any, composers would (and should) not care about them. Of course, certain combinations occur more often than others, but all are allowed and all are used, no matter if you analyze Bach or modern jazz pieces.

As for modes, in a purely modal piece (e.g. in dorian) you are not as free as in a general minor key. But this is the composer's choice because he/she decided to write a modal piece. However, all other notes can always be used as passing notes or approach notes. Here it's mainly the rhythmic placement that determines whether a passing or approach note sounds good. The notes of the mode are usually placed on stressed beats, whereas all others are usually placed on unstressed beats.

EDIT:

Inspired by a comment (see below) I'd like to give one famous example of the fact that in a minor key the major 6th, major 7th, minor 6th and minor 7th can appear in any possible combination, and that composers usually don't care much about academic guidelines (like using major 6th and major 7th ascending, and using minor 6th and minor 7th only descending, etc.). The following example is by J.S. Bach. Note the descending sequence of root, major 7th, major 6th and fifth in the last bar. And we're not even talking about 20th or 21st century music yet!

enter image description here

(from The Chord Scale Theory & Jazz Harmony by B. Nettles and R. Graf / Berklee College of Music)

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"The truth of my quote ... was doubted in another answer" yup that was me. Did you downvote me for that? Thanks alot :) So please show us some examples that contradict my explanation of how freely one can "mix an match" raised 6ths and 7ths with the natural one. –  Roland Bouman Mar 21 at 17:39
    
Great idea (the one with the example)! See my edited answer. By the way, would you mind sharing with us what your statements are based upon? –  Matt L. Mar 21 at 21:42
    
Thanks for the example. I got most ideas from counterpoint textbooks and examples, but found them to hold true also for many chord progressions. Re. your sample: I would analyse the first half as being in E minor. A dorian minor does not make sense because of the repeated use of d#. Your example does illustrate a case I did not include in my answer, the use of raised 7th and 6th in a descending pattern. However, what it does show, as I also argued is that raised/natural is used in pairs, and are not freely mixed. –  Roland Bouman Mar 21 at 23:20

There are two ways to look at to look at this question from a classical music theory perspective and modern perspective.

In classical music theory, if you are in any minor key you would use the following chords:

i iio III iv V VI viio

The viio comes from the leading tone chord found in harmonic minor. You would not want to use the subtonic chord (VII) because it is V of the relative major.

In the melody you would use the melodic minor scale when going towards the tonic chord (i) and the natural minor scale when moving away from the tonic chord.

From a modern perspective it is whatever you want and what sounds good to you. You can use v or V and VII or viio and III or III+ any combination if you want as long as it sounds good to you.

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Just to be clear, the vii° you have has a root a half step below the tonic? –  Tim Seguine Mar 20 at 13:33
    
Yes, that's what leading tone means –  Dom Mar 20 at 13:34
    
Yeah I get that, I just logically would have expected the scale degrees to be notated with respect to the key signature. I guess it doesn't work that way. –  Tim Seguine Mar 20 at 13:37
    
@TimSeguine it's a common misconception especially in minor keys because of how it's used. The harmonic minor scale is implied in minor when dominants(V and viio) are used. musictheory.net/lessons/44 and musictheory.net/lessons/50 and give wonderful explanations on this topic. –  Dom Mar 20 at 13:58
    
so would it be healthy then to just consider the chords for the minor key as being i ii° III iv v V VI VII vii° If I extend these with sevenths, which ones are the "correct" ones to use? –  Tim Seguine Mar 20 at 14:14

the 6th and the 7th scale degrees can be modified whenever the composer feels it's necessary to do so.

This is not true. If the 6th is raised, then it should typically move on the the raised 7th, and that should resolve to the tonic. These degrees would typically occur as non-chord tones, most typically as passing tones. This could happen for instance against the tonic chord.

The natural 6th and 7th degrees can be used more freely. Melodically they could also appear as passing tones in a line descending from the tonic to the fifth.

However, what you will almost never see, is a descending line starting from the tonic to the 7th, that then descends to the raised 6th; not even if that raised 6th ascends again to the raised 7th.

What might occur, but not very often is an immediate juxtaposition of the descending line on the natural 7th, 6th and then fifth and the ascending line using the raised 6th, raised 7th to the tonic. The reverse though, does occur quite often: ascending line from fifth to raised 6th, raised 7th, tonic, which then immediately descends to natural 7th, natural 6th and then fifth.

"To throw another wrench into the gears, how do other "minor" modes play into this? I am considering a scale mode to be "minor" if its 3rd is a minor third and the 5th is a perfect fifth. For example, in the dorian mode: Can I play the same tricks with the 6th and 7th there too? Or will I run into problems?"

I'd say that yes, any scale with a minor third will sound as some variation of the minor scale. You can raise the 7th in dorian mode too, and whereas the dorian mode has a major sixth normally, you can use a minor sixth too. Obviously if you do that all the time, it will cease to be dorian and sound like melodic minor.

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Maybe I should explain that the context of that statement was explaining why the dominant was a major chord instead of minor chord in that particular song. –  Tim Seguine Mar 20 at 13:13

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