Taking a simple tune consisting mostly of diatonic chords and making it sound like a jazz standard is pretty easy if you know how to apply a small handful of basic techniques:
- Identify target points
A song is made up of a series of harmonic phrases. A typical phrase length is two bars, although phrases of one and four bars are common as well. Target points are the chord that anchor these phrases – generally, the first chord of each phrase. A chord progression can be seen as a series of harmonic journeys from target point to target point.
- Substitute compatible chords at some of these target points
The I chord is often interchangeable with either iii or vi in that either of these chords can potentially work as a substitute for the tonic (and vice versa). Similarly, the ii and IV chords are also often interchangeable. If any of these chords occur at a target point, you can use make one of those substitutions at your discretion. If the V chord appears as a target point (common in very simple songs), you are almost always better off replacing it with a ii-V, because this is a more idiomatic choice of target in the jazz language. Also, while you are at it extend all chords to (diatonic) sevenths if they are not already – major seventh for I and IV, dominant seventh for V, minor seventh for ii, iii, and vi.
- Replace the approaches to the target points
Each of these possible target point chords have a handful of common idiomatic approaches – the chords at the end of the previous phrase that lead to the target. Assuming it works with the melody, you can normally swap out one idiomatic approach to a given target for another. In the phrases where you have already substituted a different chord at the target point, it can sometimes work to keep the old approach and allow the resolution to be deceptive, but normally you will want to use a secondary dominant (or secondary ii-V) or other approach that leads directly to the new target.
It takes a certain amount of experience to get a feel for how to apply these approaches. Most of it comes down to getting familiar with the various idiomatic phrases in the harmonic language of jazz standards. Of course, everyone who plays even a little jazz is familiar with ii-V-I, but there are dozens of other common phrases, such as IV-bVII7-I, I-IV-iii-VI7, etc. Elsewhere – such as in my book, The Harmonic Language of Jazz Standards – I provide more information on this. For now, I will show you how these techniques can be applied to the reharmonization of simple songs, beginning with Silent Night.
Here is the original version I am starting with:
Identify target points
For the most part, each phrase is two bars, and the target points occur at the beginnings of each of these. The one exception is bars 1-4. While it would be possible to see this as two phrases of two bars each, my sense is it might be more useful to see it as a single four bar phrase.
So basically, every single chord ends up being a target point except the G7 in bar 22.
Substitute compatible chords
The target points in this song are all I, IV, or V chords. As mentioned, we should definitely replace the V chords with ii-V’s, so measures 5-6 become Dmi7-G7. Same with measures 17-18. Because that gives us two places where the target point is the ii chord, I don’t feel the need to also replace the IV chords in bars 9 or 13.
We can replace many of the I chords. The first and last chords should stay as they are, but we can consider replacing the I chords in measures 7, 11, 15, and 19 with either iii (Emi7) or vi (Ami7). For measures 7 and 19, Ami7 is a better fit for the melody, whereas Emi7 fits better in measures 11 and 15. Realistically, I could make all of none of those substitutions and still find interesting things to do at the next stage.
Note that the I chord in second inversion (C/G ) in measure 21 actually functions as a dominant chord according to classical theory, so it isn’t clear how best to treat it here. But the melody so clearly outlines the I chord that I am reluctant to change this at all.
Replace the approaches
The first four bars need to create a route from I to ii – a type of progression I call a precadence (since it precedes a cadence like ii-V-I). A common precadence in jazz standards is I-IV-iii-VI7, so I will use that.
I will go ahead and use the Ami7 in bar 7. While I could keep the ii-V I now have in bars 5-6 after the previous stage (creating a deceptive cadence), I have decided to instead replace the G7 (which approached the original C chord) with an E7 (secondary dominant approach to Ami7). I will further expand that secondary dominant into a secondary ii-V (Bmi7b5-E7), and also use tritone substitution to replace the Bmi7b5 with F7, since the melody note (B) fits this so beautifully.
For the route from vi to IV in bars 7-8, I use a secondary ii-V in bar 8 to approach the IV (Gmi7-C7-F), and a tritone sub passing chord (Ab7) in the middle of bar 7 to connect the Ami7 and the Gmi7.
For bar 11, I have elected to keep the I chord but place it in second inversion (C/G), thus allowing me to insert a passing diminished chord (F#o7) in bar 10. I continue the chromatic motion by using a Gb7 (tritone substitution for secondary dominant) to approach the Fma7 in bar 13.
In bar 15, I am using the iii chord (Emi7), which begins a basic circle of fifths iii-VI7 approach to the ii chord in bar 17 that for some reason sounds especially satisfying to me here with the melody. Since bar 14 will sound pretty plain if I don’t put something there, I will simply use the diatonic substitution ii for the original IV chord.
In bar 19 I am using the vi chord (Ami7). I am leaving the ii-V that now approaches it mostly alone to yield a deceptive cadence, but I have added a passing diminished chord (G#o7). I also have added a tritone substitution approach to the V chord (Ab7, leading to the G7).
Since the C/G chord in bar 21 is really functioning as a V chord, it seems logical to assume a II7 chord would work in bar 20. It also fits the melody nicely, and it makes sense coming from the Ami7 in bar 19. A number of other harmonizations I have heard use F#mi7b5 here, which is largely the same sound.
The only change I make to the final cadence is to delay the final resolution to I by adding a IV chord in bar 23. Somehow the plagal cadence here seems appropriate.
Here is the finished reharmonization:
Here is a second reharmonization. See if you can figure out for yourself how I applied the same process to arrive at this one!
- I treated bars 1-4 as two separate phrases of two bars each.
- My first reharmonization lacked a minor plagal cadence, and I missed it, so I forced the issue in bars 21-22. The logic being, since the original C/G in bar 21 functions as a dominant, I can change it to a ii-V, and then substitute IV for ii, and then use the backdoor dominant Bb7. This also created an interesting approach in bars 19-20.
- The only phrase that is the same in both versions is bars 15-16, because as I mentioned before, I really like how that parts works. I will confess this is not original; I have heard other arrangements you this.