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Contents:
• General Chord Substitution
  * Extending Chords
  * Embellishing Chords
  * Combining / Conclusion
• Common Tone Substitution
• Barrowing From Parallel Keys
• Tritone Substitution
• Random Chord Substitution / Conclusion

General Chord Substitution

Replacing a chord in a progression with another similiar chord is known as chord substitution. Chord substitution a great way to spice up cover songs to make it sound a little different than the original and also to make your own songs more interesting. The chord that replaces the original chord generally has some relation to the original.

Extending Chords

Extension chord substitution involves extending the triads by adding extra notes to the triad, such as the 7th, 9th, 13th, etc. scale degrees to the chord.

NOTE: There are only 7 notes in the scale, so anything above 7 is a repeat of one of the scale degrees from 1 to 7. For example, the 9th is the same as the 2nd, the 13th is the same as the 4th, etc...

This process is pretty self explanatory, but what happens when you get up to the larger chords like 13th chords? It consists of 7 notes total, (1st, 3rd, 5th, 7th, 9th, 11th, and 13th) and there are only 6 strings on the guitar. This is where you start eliminating certain notes. In most cases, the 5th is the first to go. After that I think it becomes a matter of preference and which voicing sounds the best for the song.

"Add" chords are another way to extend a triad. An add chord simply adds the specific scale degree to the chord. For example a Cadd9 adds the 9th scale degree and the notes are C E G D.

If there is no "Add" in the chord, then you must include all of the notes created by stacking thirds onto the triad up to that specific scale degree. In other words, the Cadd9 chord differs from the C9 chord because the "add" tells you to only add that one specific scale degree (the 9th) to the chord, whereas the C9 chord also adds the 7th scale degree in addition to the 9th. Chords that don't have "add" are built by stacking thirds to get to the specified note.

13th chords are as high as you can go by stacking thirds. The 15th is a repeat of "1", so you would be starting all over again if you went any farther. To get to the 13th, you would have to stack thirds all the way up to the 13th scale degree:
1 3 5 7 9 11 13

For example a C13 chord is C E G bB D F A.

NOTE: The exception to the above rule is the 6th chord, because these cannot be built by stacking thirds. Therefore C6 only adds the 6th scale degree and nothing else (C E G A).


Embellishing Chords

By embellishing chords, you alter existing notes in the chord.

Suspended chords (abriviated "sus") change the 3rd in the chord to either a 2nd or a 4th. In other words, for sus the 3rd is not played in the chord. Sus chords are therefore neither major or minor, since the 3rd is what determinines if the chord is major or minor. You can see a comparison between these various C chords.

C major: C E G    (E is a major 3rd)
C minor: C Eb G    (Eb is a minor 3rd)
Csus2: C D G    (there is no 3rd)
Csus4: C F G    (there is no 3rd)

Augmented chords (abbrevieted "aug" or "+") sharps the 5th scale degree. This is a very short and simple explanation, because there's really not much to explain. Here is an example of the augmented chord:

C major: C E G
C+: C E G#

Combining / Conclusion

We have just covered two ways to replace basic triads with more complex chords. As you may have guessed, you can also combine both the extension and the embellishment methods to create all kinds of chords like C7sus4, or F#13b5b9, etc.... The possibilities are pretty much endless.

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Common Tone Substitution

Common tone substitution means that chords that share common notes can be substituted for each other. For example:

C major: C E G

E minor: E G B
A minor: A C E

The bolded notes are notes that the chords have in common with C.

Because Em and Am both share two notes with C, either one of them can be played in place of C (The reverse is also true and C can be played in place of either Em or Am.) This method works with a variety of chords, for example bmurnahan used 7th chords.

Cmaj7: C E G B
Emin7: E G B D

These share three notes and can be played in place of each other.

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Barrowing From Parallel Keys

Parallel keys are major and minor keys with the same tonic. Parallel keys are different from Relative keys and if there is any confusion between these, click here for explanations on both of these.

This method of chord substitution allows you to at any time borrow a chord (or chords) from the parallel key. To do this you look at the Roman Numeral chords and replace one number with the same number from the parallel key.... Let's see an example to illustrate.

If you are playing a I IV iii vi progression in the key of C major then you have the chords:
C F Em Am

To figure out what chords you could replace these with, look at these Roman Numeral chords in the parallel key of C minor. Then make the substitutions...

The chords for the key of C minor:
Cm Ddim Eb  Fm Gm Ab Bb
i  iio  III iv v  VI VII

i = Cm
iv = Fm
III = Eb
VI = Ab

Therefore you could replace the C with Cm, the F with Fm, the Em with Eb, or the Am with Ab. So now pick one of the chords from the parallel key to substitute into the original progression like the following examples.

The Bolded chord indicates the chord that was substituted.

C  F  Eb Am
Cm F  Em Am
C  Fm Em Am

etc...

That is the basic idea. For simplicity, this lesson only replaced one of the chords to illustrate the idea, but you can replace more than one chord in the progression. You can even replace the entire thing.... In fact, if you replaced all of the chords in the example above, the new progression would be i iv III VI (Cm Fm Eb Ab). This is the method used to change keys which is covered in the lesson on Modulation.

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Tritone Substitution

Tritone substitution is another form of chord substitution. The name “Tritone” means three tones (or three whole steps) which is a diminished 5th (or augmented 4th) interval. This diminished 5th interval shows up in dominant 7 chords and in diminished chords. However, for tritone substitution only dominant 7 chords are used.

The basic idea is to take the dominant 7 chord (for example G7 in the key of C major) and replace it with another dominant 7 chord that has the same diminished 5th interval (tritone) but “flipped”. For example:

G7: G B D F

B - F is the tritone in G7, so the chord we are looking for will have F – B as the tritone. That chord just happens to be a tritone (3 whole steps) away from the G7 chord, which is Db7.

Db7: Db F A Cb(B)

In this case you are barrowing a chord from outside of the key of C major, but since the Db7 has the same tritone interval, it has a similar function to the G7... That is, it will pull towards C (the tonic).

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Random Chord Substitution / Conclusion

The above examples lists several ways to substitute chords that have some sort of similiar quanity to the original chord. Of course, seeing as how these are not hard fast rules that you must follow, you can also plug any random chord in for another and simply see how it sounds. There's not much to say theoretically on this and you'll just have to let your ears guide you through this process.



* Next Lesson: Modulation