Why does a major minor modulation with the same root work (e.g. C to Cm) [duplicate]

Question

There are very few chord changes I cannot rationalize and fit into some mode of a major scale. One of these is a major minor change with the same root (e.g. C to Cm). The C chord has c, e, and g notes. The Cm has c, eb, and g notes. There is no major scale that fits these notes. Is there a scale that can be used to riff across these chord changes with impunity or must the change be noted and respected?

This question is similar to Theory behind the change from a major chord to the same in minor but I'm not seeing an answer in that post that includes a scale that includes the notes c, eb, e, and g. What scale(s) include the notes c, eb, e, and g.

These notes make up a C(#9) chord so the question could also be asked as what scale contains all of the notes in a C(#9) chord.

Answer 1

You can never have a scale that includes an Eb and an E at the same time because that would mean two notes are derived from the same root, namely E.

That is not the definition of a scale. You can only have each note once!!!

If you said C D# E -> this would be possible but that would not leave any place for a D. So you are stuck with a one-and-a-half step there. This interval can only be found in a harmonic minor scale (between the b6 and the major7) or any of the more exotic - lets call them gypsy-scales - that can have one or several one-and-a-half step intervals.

And - there are of course a lot of variants of Blues-scales that incorporate this interval, like:
C D# E F# G A Bb C
or even scales with 6 notes only, like:
C Eb F F# G Bb C

But as you see - with these 'artificial' scales you'll soon run out of arguments about how to interpret their notes. Of course you could interpret it as:
C D# E# F# G Bb/A# C
so there would be only one note derived from each root but I guess this is a little far fetched.

But with regular diatonic scales with 7 notes you should stick to the rules!

IONIAN (major), DORIAN, PHRYGIAN, LYDIAN, MIXOLYDIAN, AEOLIAN (minor), LOCRIAN

Answer 2

As pointed out in @mramosch's answer, there is no standard seven-note (heptatonic) scale containing both an Eb and an E. Also note that we're not talking about modulation when we encounter the movement C to Cm (see below for the most common occurrence of this progression without modulation).

When playing a melody over the change C - Cm you want to make the difference between the two chords clear, so you need to change scales (or only use notes that both scales have in common, but that might be a bit boring).

The most common occurrence of the progression C - Cm is actually in the key of G major. It is very common to move from the IV (C) via the iv (Cm) to the I (G). This cadence works so well because the note E in the C chord moves down chromatically to the Eb of Cm, which in turn resolves to the note D of the G major chord. Once you know how it sounds you'll start hearing it almost everywhere.

If you want to play a melody over that progression, the simplest thing is to just alter the E to an Eb as soon as you move to the Cm chord. In the key of G that would mean to move from the G major scale (C lydian) to the G harmonic major scale. Another common option is to alter two notes (E->Eb, F#->F) and play the C melodic minor scale over Cm. Yet another option commonly used is to move to G natural minor (C dorian), in which case you alter three notes of the original G major scale (E->Eb, F#->F, B->Bb).

Answer 3

The relative key modulation would not be Cmin to CMAJ but rather C minor to Eb Major the relative Major key. This will enable you to use a couple of pivot chords that smooth out the modulations.

If you have your c minor phrase and you end the phrase on the dominant you can let it resolve with the chord c-eb-g which could either be tonic chord of c minor or sub mediant chord of Eb Major which is both perfectly fine resolutions to a dominant chord.

As you rightly point out the type of modulation you mention will be hard to resolve easily for the reasons you point out. Although I can imagine somewhere in the history of music someone did a modulation in that manner it is not a very natural modulation.

The transition between keys is just important that what you modulate to and when your two keys seem to clash it is very hard to modulate seamlessly.

Answer 4

One possible answer is E harmonic minor. E harmonic minor has all of the notes I'm looking for.

http://www.jazclass.aust.com/scales/scahar.htm

Answer 5

Just for clarification about the term modulation:

As a musical term it means the process of moving to another key (as TONICA) (root) by means of a chord-progression that clearly establishes the functional part (TONICA) of the new key.

Sometimes it is enough to play a DOMINANT seventh chord to establish the new TONICA of a chord that lies a perfect 4th above the DOMINANT. This can be for two beats of a bar only, or sometimes even a single 'dominant-shot' on the last quarter note of a bar is sufficient.

If you want to hear this kind of modulation in the pure classical way listen to Puccini's Madam Butterfly where he even enforces this DOMINANT functionality with a sharp 5th (#5)in the dominant 7th chord and making a whole chain of modulation as a sequence:

C(maj7) - A7/#5 -> D(maj7) - B7/#5 -> E(maj7) - C# 7/#5 etc.

Of course this goes hand in hand with the instrumentation. For these tricks he always uses the harp, because - although being a diatonic instrument like a piano, and thus having 7 notes per octave - you can re-interpret/re-tune these strings with the pedals of a harp and finally get only the notes of this augmented dominant 7th chord. Which means you can really 'harp' up and down with both hands the full range and all strings sounding loudly at the same time (arpeggio -> arp == harp).

For other modulations you need something more sophisticated than a single dominant-7th-chord. A little cadence with a SUBDOMINANT-DOMINANT-TONICA pattern like IIm - V7 - I or IV - V7 - I or even a DOUBLE-DOMINANT pattern like II7 - V7 - I

e.g. Dm - G7 - C , F - G - C or D7 - G7 - C

My personal favorite for popular music is again from the 80's Barbra Streisand Albums where they use a pattern like:

IV/V - V -> that finally leads to -> I

to establish the new tonality. Either each chord for a whole bar or the whole set two times each chord half a bar. You can modulate from absolutely any key to any other key within a bar or two. Of course the bass note which already comprises the DOMINANT functionality has to be played decidedly while the chords above change between SUBDOMINANT and DOMINANT (IV and V).

Anything else cannot be considered as a modulation but rather a shift-over...
German has a very nice word 'RÜCKUNG' for this kind of unprepared change of tonality! It essentially means move/shift something to another place!