Question about chord progressions and scales

Question

recently I watched a Youtube Short of a short Bossa Nova chord progression, with the chords in order as follows:

Cm9 -> Fm7 -> Dm7b5 -> G7b13 -> Cm9

So I looked up the C minor scale. From there I figured that Cm9 would be the I degree, and Fm7 the iv degree.

Then I searched for a Dm in the scale, but the only D chords in the C minor scale are the ii degree (Ddim) and III degree (D#).

Since there is no Dm chord in the Cm scale, I wanted to ask: where does this chord come from? I found myself wondering the same thing with that G7b13 chord, since the Cm scale only contains a Gm chord.

I'm sure I have a fundamental misunderstanding of chord progressions, so any help would be greatly appreciated! :)

Answer 1

The Dm7b5 is the chord built on the second degree of C minor. The triad built on D in C minor is diminished, it is D-F-Ab but if you extend it to a 7th chord it becomes D-F-Ab-C which has two names, D half-diminished or Dm7b5. It is not a full diminished 7th because a full diminished 7th would be all m3 intervals and have a Cb instead of a C.

As for the G7b13, that chord which in its basic form is simply a G7 is the V7 dominant chord in C minor, which is created by using the harmonic minor scale with a B natural instead of a Bb. That allows you to have a dominant to tonic relationship in minor keys instead of just Vm to Im, or Gm to Cm. The b13 is simply an upper chord extension added for color and complexity.

This makes the entire progression Im9-IVm9-IIm7b5-V7b13-Im9. If you are familiar with 2-5-1 progressions at all this is the way they are typically done in minor keys, with the m7b5 instead of the m7 for the 2 chord,

One more comment, the 3rd degree of Cm is Eb, not D#. C minor has three flats, one of which is Eb, but no sharps. When in doubt, each letter only gets used once.

Answer 2

where does this chord come from?

A D minor chord in the key of C minor comes from chromatic alteration. The pitches are D, F, and A. But the diatonic sixth degree of C minor is A flat, not A natural. By raising the A flat to A natural, you can obtain a D minor chord in C minor.

However, the chord you're asking about isn't a D minor chord. It's a diminished chord, or perhaps more precisely an extension of that chord. Classical theory calls it a half-diminished seventh chord, because the fifth is diminished but the seventh is not. Notice the "♭5" portion of the chord symbol. This specifies that the fifth of this chord is a diminished fifth above D, namely A flat, which is the diatonic sixth degree of the C minor scale.

I am not sure why jazz theory abandoned, as they seem to have done, the degree symbol for diminished chords and half diminished seventh chords. I (as a primarily classical musician) find D^ø7 more concise and easier to read than Dm7♭5. But I'm not in the target audience, so my opinion should perhaps be discounted somewhat.

(Some may want to go into the confusing discussion of whether one is talking about the C natural minor scale, or harmonic minor, or melodic minor. The harmonic minor and melodic minor are best thought of as chromatic alterations of the natural minor scale, consistent with their notation using accidentals. Therefore, even if you prefer to think of D minor as coming from the melodic minor scale, I would still say that it is the result of chromatic alteration.)

One of the oldest chromatic alterations in the books is the raising of the leading tone in final cadences when the diatonic seventh degree of the scale is a whole step below the tonic. This long predates tonal harmony and in fact was one of the main factors leading to the development of harmonic theory. For this reason, one of the basic rules in harmonic theory is that when there's a chord built on the fifth degree of the scale (G in this case) the third is raised if the following chord is built on the tonic (C in this case) -- as well as in some other situations. This gives us a major triad (or a dominant seventh chord). In this case, it gives us G7♭13 instead of Gm7♭13. You could call this "using the harmonic minor scale" for that chord, but either way it is an example of chromatic alteration.

Answer 3

'So I looked up the C minor scale'. That's the beginning of where it went wrong!

You found the natural minor scale - with 3 flats, the relative minor to E♭ major. Trouble is, there are two more C minor scales, the notes of all which get used in pieces in key C minor. So, the first five notes of all those are C, D, E♭, F, G. But the remaining notes are all the chromatics from A♭ through to B♮. And the 'wrong' notes you quote will be found in there somewhere!

There's also this misconception that all notes in a piece in a particular key must be from that key. Not true, by any means. A common ploy is to use those notes from the parallel key - here, C major. Which gives composers a much larger selection of notes with which to play - literally. In fact, looking at many pieces, all 12 chromatic notes are up for grabs, with various excuses (theoretical reasons) as to why they can be and are used.