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It's possible to harmonize a descending chromatic scale with consecutive dominant 7ths(the most common way), but that goes down the circle of fifths and takes the piece to a distant key. Is there any way to harmonize a partial descending chromatic scale in a way that it remains in the original key? I know that the chromatic scale will inevitably stray from the key somewhat, but how can I harmonize a descending chromatic scale to stay in the key as much as possible?

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    Depending on what you consider to be acceptable harmony, the answer could trivially be "yes". All you would need to do is consider each non-diatonic melody note an altered extension of the diatonic chord you are "harmonizing" it with Commented Apr 16, 2023 at 4:38
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    How much of a descending chromatic scale are you considering?
    – Tim
    Commented Apr 16, 2023 at 7:46
  • @Tim scale degree 1 to flat 6 and(at a different point) 5 to 3, all in major key.
    – OprenStein
    Commented Apr 16, 2023 at 20:17

3 Answers 3

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Notes

  1. This post considers "chromatic descent" as being two or more consecutive half steps. The single half-step cases are trivial, since both major and minor contain them natively.

  2. Scroll to the bottom for a Chopin example.

Discussion

By definition, chords "in a key" may contain only notes within that key.

However, there are exceptions, depending on how strictly one defines "in key".

  1. Strictest definition: Every pitch must be a part of the key as defined by its key signature.
  2. Leading tone exception: In minor, the seventh degree of the scale may be raised to form a leading tone.
  3. Allowing modal mixture: Minor and major keys may incorporate each others chords provided the overall tonic remain the same.
  4. Allowing "chromatic" chords: Chords like bII and aug6 may be used without considering them as out of key.
  5. Allowing altered extensions to diatonic chords: By allowing use of b9, #9, #11, etc., chromatic notes can be accommodated in otherwise diatonic (seventh) chords.
  6. Allowing secondary dominants: Individual secondary dominants can be used to accentuate specific chords within the key.
  7. Allowing more general tonicizations: Other secondary chords and brief secondary passages may be used provided the large-scale tonic remains intact.

Illustrations

  • Using (1) or (2), it's impossible to use any chromatic notes in major.
  • Using (1), it's impossible to use any chromatic notes in minor, but by using (2), it's possible to harmonize 8-7-b7 (i - V - v).
  • Using (3) allows harmonization of 8-7-b7-6-b6-5 and 4-3-b3-2.
8  7 b7  6  b6 5
I  V  v  IV iv I
  • (4) – (6) all allow full harmonization of the chromatic scale.
8  7 b7  6  b6  5 #4  4  3 b3  2 b2  1
I  V  v  IV iv  I V/V V7 I  i  V bII I

Chopin example

Chopin gives a beautiful example of harmonizing a chromatic descending bass in his Prelude in C minor (op. 28 no. 20 [IMSLP]).

The progression (in C minor) is

i  VI6  [chromatic passing chord = Ab-7b5]  v6  ii7/V  Fr.Aug6  V#  V#42  i6

Chopin Op. 28 No. 2 mm. 5–7b1
(Image Source: IMSLP, Knute Snortum edition)

The chromatic bass actually ends in m. 6b3, but I've included the next couple of chords since they continue the overall scalar descent.

The passage can be heard on YouTube, performed by Artur Rubinstein.

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    Minor v, iv, and i could be replaced with major chords where the melody note acts as a #9 (AKA Jimi Hendrix chord). Perhaps another way to look at my comment is suggest a point 7. that is something like "altered extensions of diatonic chords could be used". #5, b5, #11, #9, b9, #13, b13 Commented Apr 16, 2023 at 4:40
  • @ToddWilcox Great comment. Added. (Inserted as new point 5.)
    – Aaron
    Commented Apr 16, 2023 at 4:47
  • Why VI with 6 and vi with b6? Shouldn't it be opposite? Commented Apr 17, 2023 at 21:44
  • @user1079505 It's IV and iv, not VI and vi. The IV chord included the major 6, and the iv chord includes the minor 6.
    – Aaron
    Commented Apr 17, 2023 at 21:56
  • Alright, I can't read then, sorry! Commented Apr 17, 2023 at 22:06
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enter image description here

C, G7, C7, F, Fm, G/C, D7, G7, Am, D7(♭9), G9, D♭7/G, C6.

CORRECTION bar 2 beat 2 is C/G of course.

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A descending chromatic bass over the upper tetrachord (8 down to 5) has been used rather often. https://musictheory.pugetsound.edu/mt21c/DescendingChromaticBassLines.html#:~:text=A%20common%20musical%20pattern%20is,from%20the%20past%20four%20centuries. Beethoven's version is interesting in that it keeps the feeling of C minor throughout.

i-V6-I42-IV-Ger6-i64-V

One could attach Aaron's suggestion to this to go through the whole thing.

Some Baroque pieces used the Omnibus Progression or a close wedge-progression variant. https://en.wikipedia.org/wiki/Omnibus_progression

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