Chord Substitution - Enharmonic Equivalents - Altered & Extended Dominant Seventh Chords

Before tackling the six enharmonic chord examples, it is important to master these three theoretical notions :

• Extended Chords.
• Altered Chord.
• Enharmonic Equivalents.

What's An Extended Chord?

An extended chord is a chord that includes intervals beyond the basic triad (which consists of the root, third, and fifth notes of a scale).

Extended chords include additional tones stacked on top of the basic triad, usually the seventh, ninth, eleventh, and thirteenth notes of the scale.

Here are some common extended chords:

- Seventh Chords: These include the seventh note of the scale in addition to the root, third, and fifth. Variations of seventh chords include major seventh (maj7), dominant seventh (dom7), minor seventh (min7), and half-diminished seventh (m7♭5 or ø7).

- Ninth Chords: These chords add the ninth note to the basic triad and seventh chord. Variations include major ninth (maj9), dominant ninth (dom9), minor ninth (min9), and diminished ninth (dim9).

- Eleventh Chords: These chords add the eleventh note to the basic triad, seventh, and ninth chords. Variations include major eleventh (maj11), dominant eleventh (dom11), minor eleventh (min11), and diminished eleventh (dim11).

- Thirteenth Chords: These chords add the thirteenth note to the basic triad, seventh, ninth, and eleventh chords. Variations include major thirteenth (maj13), dominant thirteenth (dom13), minor thirteenth (min13), and diminished thirteenth (dim13).

What's An Altered Chord?

An altered chord is a chord that includes at least one note that has been raised or lowered by a semitone (half step) from its original position in the standard major or minor scale.

These alterations typically involve changing certain intervals within the chord, most commonly the fifth, ninth, eleventh, or thirteenth.

The alterations in an altered chord often include:

• ♭5 (flat five): Replacing the perfect fifth with a diminished fifth.
• ♯5 (sharp five) or +5: Raising the perfect fifth by a half step, creating an augmented fifth.
• ♭9 (flat nine): Lowering the ninth note of the scale by a semitone.
• ♯9 (sharp nine): Raising the ninth note of the scale by a semitone.
• ♭13 (flat thirteen): Lowering the thirteenth note of the scale by a semitone.

What Are Enharmonic Equivalents?

Enharmonic equivalents refer to notes that sound the same but are written differently.

In Western music theory, the concept of enharmonic equivalents arises due to the use of different names for the same pitch.

For instance, notes such as C♯ (C sharp) and D♭ (D flat) represent the same sound on a musical instrument, but they are notated differently.

Here are a few examples of enharmonic equivalents:

• C♯ and D♭
• E♯ and F
• G♯ and A♭
• B♯ and C
• F♭ and E

These pairs represent the same pitch but might be notated differently based on the context, key signature, or harmonic function within a piece of music.

Dominant 7 Harmonic Equivalents

The exercise below implies six dominant seventh chords that are : G7, G7b9, G7(9), G7(b5), G7 (b5, b9), G7 (b5, 9).

You will see how they relate to six other types of chords that are : Dm6 (11), Ddim7, Dm6, Db7 (b5), Db7, Db7 (#5). 

Example 1

This first example implies a G7 chord with the fifth in the bass (G7/D) which is voiced : 5 (D), 1 (G), b7 (F) and 3 (B).

When considering the fifth of G7 (D) as the tonic note, you get a new chord named Dm6 (11), voiced this way : 1 (D), 11 (G), 6 (B), b3 (F).

Notice that there is no fifth in it, even if theoretically there should be one.

Example 2

In this second example, you see a comparison between a rootless G7b9 and a D diminished 7 chord.

The G7b9 chord is made of : D (fifth), Ab (flat ninth), B (major third) and F (minor seventh).

The fifth (D) is actually the root note of its enharmonic equivalent Ddim7, built this way : D (root),  Ab (diminished fifth), B theoretically Cb (diminished seventh) and F (minor third).

Example 3

This third chord voicing shape represent two chords: 

• A rootless G7(9) chord : D (fifth), A (ninth), B (third) and F (minor seventh).
• A Dm6 chord : D (root), A (fifth), B (sixth) and F (major third)

Example 4

Here is another example implying a rootless G7(b5) and a Db7(b5) chord which has its root note a tritone away from the root of G7.

This is what we call a "Tritone Substitution".

• G7(b5) : Db (diminished fifth), G (root), B (major third), F (minor seventh).
• D7(b5) : Db (root note), G (diminished fifth), B (minor seventh), F (major third).

Example 5

This example show how a basic Db7 chord shape can be seen as an altered rootless dominant 7 chord (G7b5b9).

Indeed, you can see and hear that it highlights two altered notes, the b5 (Db) and b9 (Ab) of G7.

Example 6

This example has a slight difference with the previous one.

The note on the fourth string has been raised by a semitone, thus highlighting the ninth of G7 (A) and the augmented fifth of Db7.