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What is the theory behind cord and harmony relationship? For the bars at the top of the page?

Jazz Exercise #2

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    Welcome to Music: Practice & Theory! Do you by any chance have an image of these last 12 bars? – Richard Apr 9 at 23:15
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    The only explicit scales I see in the image are in its 1st and 3rd measures. Do you mean those scales? – Dekkadeci Apr 10 at 5:30
  • @Peter - I agree with @Ringo's answer here. It seems like you are confused between "keys" and "scales". They are two very different things and in these last twelve bars, the only apparent scales are in the first and third measures, like @Dekkadeci said. – AduyummY Apr 10 at 18:39
  • I don't think the confusion is scale versus key, but probably scale versus chord. @Peter you used the tag "chord-theory" in addition to "scale." I think you will get more out of analyzing the chords or more generally asking "how does the harmony work." Maybe edit your question so people don't quibble about definitions of a "scale." I'll try posting an answer after I play the music tonight. – Michael Curtis Apr 10 at 21:25
  • Thanks everyone and yes Michael my question is in relation to the cord and how the harmony work together, the suggestion below that it is chromatic could be correct. – Peter Apr 10 at 22:32
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My copy of the music has 3 sections divided by double bars. The measure numbering is 1-16, 17-25, 26-33. That's 16 + (8+1) + 8 bars for the section lengths. I'm not sure why you ask only about the end of the middle section. I'll include the whole middle section along with the ending.

The chords:

|B7   |Em      |B7    |Em     |
|A7   |D       |Am7   |D7     |G D7 ||
|G G7 |C C#dim7|D6 Em7|A7 D7  |
|G G7 |C C#dim7|D6 Em7|A7 D7 G||

A few structural notes, because they are important to understand what's going on...

  • B7 to Em, two bar phrase is repeated to make 4 bars, B7 is outside the key G major, but it is the secondary dominant of Em
  • the bar I list as Em sort of looks like an odd scale, because it has a lot of step-wise movement, but it really just adds a bunch of non-chord tones to decorate a broken chord
  • the next 4 bars are a harmonic sequence meaning the B7 to Em idea is dropped down a step to A7 to D, there are two small modifications in that the D is a major chord instead of minor like the Em, and when the A7 to D is repeated (following the pattern of the original B7 to Em idea) the A7 become a minor Am7, these changes in chord quality major/minor are common in harmonic sequences, the repetitions that happen in harmonic sequences can be chromatic or diatonic the choice is a matter of style and preference
  • the change of A7 to Am7 above also reflects a pretty common thing in jazz which is a change from major quality to minor quality, sometimes it happens directly from one chord to the next, in this case there is a D chord in between
  • the third section is a 4 bar phrase repeated with alternate endings, this kind of phrase structure is called a period, the harmony G G7 C involves the G7 which is technically outside the key of G major, this is another example of a secondary dominant, this time of the C chord, it is a very common move that emphasizes the subdominant tonal region, there are more secondary dominants but I won't list them all

I imagine your initial question was about all the various sharps and flats found in the score which don't belong to the key G major. That could make a person wonder if some strange scales from other keys were being used. As you can see those chromatic tones come from the harmony and all the chromatic chords are explained as secondary dominants.

I can't help but point out how this exercise from Peterson reflects so clearly a classical music convention. In a short work like this it is very typical of classical music to place the periodic phrases at the opening and closing sections, and put the sequential harmony passages in a middle section as a kind of bridge. Obviously Peterson is showing a classical sensibility. He even titled the other pieces in this collection 'minuets' and 'etudes.'

I didn't explain every concept in detail, but I emphasized in italics several topics which you can look up for further study. A good theory textbook will explain all of them.


EDIT

Just adding my written notes, 'cause they're there...

enter image description here enter image description here

You can see some chords are anticipated being struck just before the barline or the next strong downbeat.

  • I added the image, but the score I found wasn't divided into sections, and I just went with the "12 last bars" mentioned in the title of the question. – Your Uncle Bob Apr 11 at 2:24
  • Ah! I thought the OP added the image. No problem, I just covered a bit extra, I thought it would make things clearer to see the bigger picture. – Michael Curtis Apr 11 at 2:39
  • Yes, I thought I’d be asking a bit much if I went with all the questions I had, now I can study this piece in detail – Peter Apr 11 at 11:44
  • Really appreciate the detail Michael, will enjoy working through this – Peter Apr 11 at 11:55
  • Practicing now and really getting a stronger feel with the cords, thanks again this is brilliant- always wonder why this info is not included in the book – Peter Apr 11 at 23:57

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