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As I understand it, the natural minor key will allow these chords: i, ii0, III, iv, v, VI and VII.

So, for example, these are the possible chords in the 'natural' Cm scale: Cm, Ddim, EbM, Fm, Gm, AbM, and BbM.

Add to this, the "Bdim" as an allowable chord for the 'harmonic' Cm scale.

And finally, add to this, the "Bdim" and "Adim" chords as allowable for the 'melodic' Cm scale.

So, my question is why (according to the MUSIC THEORY for DUMMIES book) are these chords: Dm, Ebaug, FM, and GM additional possibilities that are allowed in the Cm scale?

Each of these 4 chords has to be modified with natural symbols to fit in the key signature so it surprises me that they should be there.

Thank you, Dan

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  • This question is asked using incomplete, thus false, premises.
    – Tim
    May 24, 2022 at 7:15
  • @Tim I have expanded my answer in an attempt to address that.
    – phoog
    May 24, 2022 at 7:40
  • Get one concept clear. We can take a scale, and list the chords that can be constructed from those notes. But that isn't the list of what is ALLOWED. It's just a list of plain vanilla chords in that key. Chocolate and strawberry are also on the menu!
    – Laurence
    May 26, 2022 at 14:56

3 Answers 3

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The G major triad uses pitches that appear in both the C harmonic minor scale and the C melodic minor scale, namely G, B, and D. In fact, the tendency to use a major triad on the fifth degree of the scale predates by a few centuries the idea that there are multiple forms of the minor scale, and the tendency to raise the seventh degree (B flat to B natural in C minor) predates the development of harmonic theory by a few more centuries.

The multiple forms of minor scales were invented in the 19th century to reconcile the many different chords that can appear in minor keys (for example, that pieces in C minor frequently have F major and G major chords as well as F minor or G minor). Trying to determine what chords are "allowed" by various scales is more or less what my grandfather liked to call "bass ackward."

Each of these 4 chords has to be modified with natural symbols to fit in the key signature so it surprises me that they should be there.

The same is true of the harmonic and melodic minor scales. This is one clue that scale is not the same as key. Similarly, pieces in C major also frequently contain D major chords or C7 chords, which require chromatic alteration. This has its roots in the phenomenon of the secondary dominant, as Tim notes in his answer, but nowadays they can arise for other reasons as well.


In a comment, you say

I'm looking for a rule (I live by algorithms) why A♮ and B♮ are not in the key of Cm and yet those 4 chords I singled out are part of the Cm family of chords!?

Here you go:

  1. A cadence has a target pitch. This is most commonly the tonic pitch of the key (e.g. C in C minor).
  2. The standard cadence approaches the target pitch from the pitch immediately above the target pitch (e.g. D-C in C minor).
  3. The second voice in a standard cadence approaches the target pitch from the pitch immediately below (e.g. B♭-C in C minor).
  4. Immediately before reaching the target pitch, the two voices should be separated by a minor third or major sixth. If the diatonic pitches surrounding the target pitch are separated by a major third, raise the lower pitch (or, less commonly, lower the upper pitch) by a half step (e.g. B♭ becomes B♮).
  5. If the previous operation results in a melodic augmented second in one of the parts (e.g. A♭-B♮), alter the previous note to make it a major second (e.g. A♮-B♮).

This is more or less the standard explanation for the existence of the harmonic minor and melodic minor scales. These scales are part and parcel of minor-key tonality.

In the late middle ages and the Renaissance, these rules led to the development of something called musica ficta or "false music." That's because the raised leading tone (e.g. the B♮ in C minor) was frequently outside the set of "allowed" notes. In time, however, the raised leading tone came to be considered an integral part of minor-key tonality. By that time, around 1600, the rules above had evolved into something like this:

  1. A cadence has a target pitch. This is most commonly the tonic pitch of the key (e.g. C in C minor).
  2. The bass part in a standard cadence approaches the target pitch from the pitch a perfect fifth above (or a perfect fourth below; e.g. G-C in C minor).
  3. The next-to-last chord in a standard cadence has a major third (e.g. B♮ in C minor).

In your question you write

Add to this, the "Bdim" as an allowable chord for the 'harmonic' Cm scale.

And finally, add to this, the "Bdim" and "Adim" chords as allowable for the 'melodic' Cm scale.

The problem with this reasoning is that you're only using the "extra" notes that you get from chromatic alteration (that is, the extra notes that you get from including the harmonic and melodic minor scales) as roots of chords. But they can also be used in other positions. So, in C minor, A♮ can also appear as the fifth of a D minor chord or the third of an F major chord. With B♮, not only can it appear as the third of a G major chord, but using B♮ as the third of a G major chord in C minor is precisely why we have the harmonic and melodic minor scales!

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  • Thanks, but I'm looking for a rule (I live by algorithms) why A♮ and B♮ are not in the key of Cm and yet those 4 chords I singled out are part of the Cm family of chords!? May 23, 2022 at 22:21
  • @user3216617 I love algorithms too, but not everything can be explained by algorithms. In particular, you can't really generalize a rule from a single phenomenon, nor does it serve much purpose. The best explanation for the set of chords used in minor keys comes from the history of harmony and, earlier, counterpoint.
    – phoog
    May 24, 2022 at 6:52
  • @user3216617 I've expanded the answer.
    – phoog
    May 24, 2022 at 7:33
  • The first sentence needs 'in key C minor', to make better sense, I think.
    – Tim
    May 24, 2022 at 8:16
  • Fine - someone would have used it for a dv I'm sure!
    – Tim
    May 24, 2022 at 8:44
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The F major and G major are secondary dominants. They can (and often do) lead directly to B♭ major and C minor, respectively. Secondary dominants abound in music - they're probably the next go-to chords after those made diatonically.

E♭+ is made up from E♭, G, B♮ - The E♭ and G are diatonic, and the B can be seen in both C melodic and harmonic minors, so that's diatonic too.

Dm, made up from D, F and A - escapes me! D major would be a better bet, again as it's a secondary dominant (to Gm). There are a couple more too...

Glad you put "allowed" in inverted commas - "expected" may be more appropriate, and I'm sure better words are out there!

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  • I personally find that IV does not lead to VII more often than it leads to VII in the music I've listened to. (Admittedly, the first two examples I can think of for IV leading directly to i in music are "The Legendary Air Ride Machine" from Kirby Air Ride and "Strike the Earth!" from Shovel Knight, so maybe your claim holds true for classical music.)
    – Dekkadeci
    May 22, 2022 at 21:19
  • Thanks for your reply, but I'm still not following why the B♮ is allowed since it is not part of the key. Is there a rule that supports this? Secondary dominants are new to me so thanks for that info. May 23, 2022 at 22:17
  • 1
    @user3216617 you mention the melodic and harmonic minor scales in the question. Since you are aware of those scales, which include B♮, you are aware that B♮ is in fact part of the key of C minor. Perhaps you should be asking about why minor keys have so much chromatic alteration rather than about why they include certain chords.
    – phoog
    May 24, 2022 at 6:58
  • @Dekkadeci "does not lead to VII more often than it leads to VII"? Anyway, the so-called plagal cadence (IV-I or iv-i) is common in classical music. It's also common to raise the third of the tonic chord in minor, the "Picardy third," but not of the IV chord. One can lower the third of the IV chord in major, i.e., IV-iv-I, but I tend to think of that more as borrowing ii65 from the parallel minor.
    – phoog
    May 24, 2022 at 7:45
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Put all the notes in all 3 of the natural, harmonic, and melodic minor scales together and you'll find that the ^6, ^♯6, ^7, and ^♯7 scale degrees are all allowed in minor keys (assuming we're using the natural minor's key signature here). This means that any triad including any of these scale degrees is allowed in a minor key.

This includes, in C minor (we'll gloss over the fact that I've labelled these scale degrees with sharps even though they use naturals in sheet music):

  • Dm (uses ^♯6 = A♮)
  • E♭aug (uses ^♯7 = B♮)
  • FM (uses ^♯6)
  • GM (uses ^♯7)
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  • A♮ and B♮ are not in the key of Cm which is the point of my question. So why are those 4 chords I singled out part of the Cm family of chords? May 23, 2022 at 22:07
  • @user3216617 - Yes, A natural and B natural are in fact in the key of C minor. The only three notes in the chromatic scale not in C minor are C sharp/D flat, E natural, and F sharp/G flat (and, even then, tonicizations and Neapolitan chords can give those notes reasonable excuses to be put in a C minor piece). Be careful not to mix up minor keys with the natural minor scale.
    – Dekkadeci
    May 24, 2022 at 3:52
  • @user3216617 your question shows that you are aware of the three supposed types of minor scales. The key of C minor uses all of those scales.
    – phoog
    May 24, 2022 at 6:54
  • @user3216617 - there is a big difference between a scale and a key. That is the part that is confusing you - thinking they are one and the same. There are many questions and answers on this site referring to the two in conjunction, and worth reading, particularly regarding minor scales and keys.
    – Tim
    May 24, 2022 at 7:11

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