If you want to study the harmony of jazz, you're going to have to head to Tin Pan Alley. Jazz players used songs from the Great American Songbook as vehicles for jazz improvisation. They played the melodies instrumentally (or sang them if a vocalist was involved) at the start of the tune; this is called playing the head of the tune. Once that was done, the chords that formed the harmony of the song remained while the soloist improvised a new melody; this is called blowing on the changes. At the end, they'd play the melody one last time and that was it.

Because jazz players favored these songs so much, their melodies and harmonies became the foundation for jazz harmony. These songs became the songs that all jazz players know and play today; they are aptly referred to as standards. The harmonies of these songs have some regular patterns that appear over and over again, and thankfully can be studied. Start with the diatonic progressions.

The Diatonic Progressions

In jazz, if you simply take the diatonic major scale and harmonize each chord up to the seventh, you can learn a lot about how jazz harmony functions. FIGURE 13.2 shows the A major scale harmonized in seventh chords.

You'll be happy to learn that the basic jazz progressions are diatonic and still follow the chord ladder. Start with the mighty jazz progression of the ii–V–I.

In jazz, nothing is more common than the ii–V–I progression. Look at FIGURE 13.3.

If jazz harmony were distilled to one central point, it would be the ii–V–I progression. It's simply all over jazz music. Sure, it gets more complicated, but the ii–V–I is the basic harmonic unit that all jazz players use.

What's interesting is that a ii–V–I is a substituted IV–V–I (as ii and IV substitute for each other), which is just a I–IV–V (remember those simple primary chords) reordered. Why change the IV to ii? By doing so, you create three different chords: a minor seventh chord, a dominant seventh chord, and a major seventh chord. That sound became the sound that made jazz sound different than other styles of music.

Add some extended chords and you get a very distinctive jazzy vibe out of this progression. See FIGURE 13.4.

Add a few more chords before the ii, and you reach the other common jazz progression, the iii–vi–ii–V–I. See FIGURE 13.5.

Minor Progressions

There is a minor key equivalent to the ii–V–I progression in major. It's still a two–five–one, but the qualities of the chords change. Instead of Dm7–G7–Cmaj7 (in the key of C major), the progression becomes Dm75–G7–Cm7 (FIGURE 13.6).

This progression is easy to spot because you also have three distinct chords, with a dominant chord in the middle. Look for the min7 5, that's usually the signpost that screams, “Hey, minor two five coming,” and see if the chords that follow it line up.

Now, look at how a real jazz tune is put together. figures 13.7 and 13.7a present a very common standard, without the melody, just the changes (jazzspeak for the chords).

Notice the analysis under the chords. There are loads of ii–V–I progressions, in many keys, both major and minor. This is very standard practice for jazz (changing keys often), but beyond that, the progressions are fairly simple; it's just modulating often.

Substitutions and Enhancements

One of the cornerstones of jazz is the ability to change aspects of the harmony as you see fit. Listen to ten different versions of the stalwart standard “Autumn Leaves,” and you will hear strikingly different approaches to a tune that is known by practically every jazzer in the known world. The reason that you can change things up so much lies in the essence of jazz substitution.

As you saw in FIGURE 13.7, jazz harmony is expressed as written chord symbols. The player has to realize these chord voicings and play them in her own way. There is no set way to voice C Major 7 on the piano or guitar; there are literally hundreds of different ways to play the same chord (see The Everything® Guitar Chords Book as an example). You rarely get the written voicings; it's always up to you to voice the chords as you see fit.

When you voice the chords, you can enhance the chords; actually, you're expected to do so. Think of it as supersizing. You see a C Major 7th chord, but that's really just a suggestion. It's telling you that you need to play a chord in the family of C Major 7th, but you are free to extend it as you see fit. C Major 7th could just as easily be C Major 9th; it's up to you. This is one of the nice freedoms afforded to you as a jazz musician.

It's also true in reverse; if you see a very tall chord, you have the chance to reduce it to its smallest part. If you see an F13th chord, you can say to yourself, “Okay, it's just an extended dominant seventh chord, I can reduce that chord to F7.” Doing so isn't wrong; actually, it's pretty common. The only thing to ponder is why you would see such a tall chord. Sometimes composers put them in there for a very good reason. Often a chord exists because it supports a particular melody note (the melody is the thirteenth). You should try to learn to play every chord you see, but that's another story. Reducing is fine, with one notable exception: alterations.

Chord Alterations

A chord alteration, as discussed earlier, is tampering with the fifth or ninth of the chord in some way. You typically see this on a dominant chord, although you could see it anywhere. Chord alterations are not something that you can typically ignore. They are always there for a good reason. Usually they support a melody note of some sort.

Here are some conditions to keep in mind when dealing with altered chords.

• When in doubt, play them as written.

• Alterations to the fifth must be played as they affect the core triad.

• Alterations to the ninth don't have to be played as long as you reduce to a seventh chord and leave the ninths out altogether.

• It's probably not a good idea to extend an altered chord any higher than written. Altered chords can have funny extensions that are not clear and expected. When in doubt, play what you have.

• Always look at the melody that goes with the altered chord. Is the melody note the reason for the alteration? If not, why alter the chord at all? Maybe it's altered for harmonic color and beauty and not necessarily function.

These tips will assist you in understanding why you see altered chords, when to use them, and how to play them.

Lots of dominant chords are altered because as dominant chords, they typically function as V chords in jazz, so they will resolve to I. Because they are V chords and they resolve to I strongly anyway (because of the pull between the third and the seventh), composers and players like to alter them as the alterations have little effect on the V chord's proclivity to resolve. You simply end up with a more colorful chord, which is a very jazzy thing.