Sixth Chords

1. Sixth Chords

A chord consisting of three tones is a triad, and a chord consisting of four tones is a tetrad. And when it comes to tetrads, the typical ones are the seventh chords. However, if there’s an option to add the 7th degree, it’s natural to consider adding the 6th degree as well. That’s what we’ll explore this time – the Sixth Chords.

Following the same principle as the seventh chords, adding the 6^th note to a C major chord is notated as “C6“, and adding the 6^th to a C minor chord is notated as “Cm6“.

Note that the symbol “6” always means major sixth (9 semitones), not minor sixth. In the examples above, do–la, fa–re, re–ti are all in the major sixth interval. Chords with minor sixth intervals are a bit more advanced so we’ll cover them in Chapter IV.

Diatonic Sixth Chords

Among the prime chords, all the major chords and II_m can turn into a sixth chord without involving accidentals.

These are the sixth chords that are diatonic to the key, very easy to use. Let’s look at the usage of sixth chords.

2. Use as Suspensions

In the Shell Theory of Melody Chapter II, we discussed the differences in roles based on the odd/even intervals. The even degrees creates musical tension––Through the study of sus4/sus2, I believe you have gained a clearer understanding of their features.

The 6^th of the sixth chords, being also an even-degree tone, shares some characteristics with sus4 and sus2. One of its uses is to create suspense or tension, especially with I or V chords. Progressions from a sixth chord to the normal triad can form a subtle tension/release structure.

III_m7IVV_sus4V

Here is an example of using sus4. Let’s change this to a sixth chord.

III_m7IVV₆V

And this is a pattern using the Sixth Chord! In this case, creating resolution from mi to re. As it involves a whole-tone movement, it doesn’t have the same feel of instability as sus4, offering a more subtle sense of anticipation.
When using this approach, it’s worth considering omitting the resolved note (re in this case) from V6 (resulting in the triad so–ti–mi) to maintain an appearance of resolution note, just like Vsus4 doesn’t contain ti.

3. Use as a Mudiness

On the other hand, there are situations where a sixth chord is used not for a suspended effect but to add a sense of murkiness, similar to the 7th.

I6I_Δ7I6I_Δ7

In this way, the sixth chord produces a murkiness distinct from the seventh chord. When a simple triad feels insufficient but a seventh doesn’t quite fit, the sixth becomes a compelling option.

IV6 is Useful

The IV₆ chord, in particular, is very versatile, providing a subtle melancholic touch.

IV6VI_m7IV6VI_m7

This creates a subtle shadow of melancholy. As the 6^th in IV is re, viewed from the kernel perspective, it provids a floating sensation.

Here is an example. In the slow progression of IVIVI during the intro, the lead guitar introduces the re note during IV, forming the sixth chord. Despite the strong distortion on the guitar, the addition of the 6^th introduces a mellow quality, different from the powerful impact of a simple power chord.

4. Minor Sixth Chords

Adding a 6^th to a minor chord constitutes the “minor sixth chord.” Within the prime chords, II_m6 is the only one that can be created without accidentals. In III_mVI_m, simply adding the 6th along the scale results in a “minor 6th” interval, different from the regular sixth chord. Trying to create “IIIm6” or “VIm6” introduces sharps, making them less practical.

II_m6VI_mII_m6VI_m

Here is an example of II_m6. With the inclusion of fa and ti, it shares a somewhat similar sound character to V₇ as a whole. Therefore, placing a tonic chord after it, as shown in the previous example, nicely liquidates the sense of instability. Of course, it’s also possible to follow it with a dominant chord tho.

With its mature flavor, this chord is perfect for evoking a nostalgic touch. It can also be a distinctive seasoning when you want to add a unique touch to II_m.

5. Similarity to First Inversions

You may have already noticed, but a sixth chord shares similarities with the chord 6th above it (=3rd below), naturally because it adds sixth degree to the chord.

More precisely, it can be viewed as the “first inversion of the seventh chord 3rd below”. Since both chord names refer to the same set of notes, either notation is acceptable¹.

The melancholic feel inherent in I₆ and IV₆ can partly be attributed to their similarity to these minor chords.

Use as Substitute Chords

In that case, the idea of substituting VI_m7 with I₆ or II_m7 with IV₆ naturally comes to mind. This is very similar to converting chords to their “first inversions”.

IV6VI_m7IV6I6

Here, based on the previous track, the last VI_m7 is replaced with I6. Given the context, this I6 has a quite similar quality to the VI_m chord. It resides in an ambiguous territory, making it unclear whether it originates from C or Am.

There’s no need to definitively choose one or the other. This means that you’ve entered the realm where a chord can hold multiple contexts together. Just like seventh chords greatly expanded the range of sound variations, sixth chords can also be utilized for various effects depending on the musical context.

Summary

• A four-note chord created by adding a major sixth interval to a triad is called a “sixth chord”.
• In prime chords, sixth chords can be formed without accidentals in the case of III_mIVV.
• Main uses of sixth chords include creating tension similar to sus4 or adding a mellow quality akin to seventh chords.
• Sixth chords share a common structure with the first inversion of seventh chords, allowing for creative applications based on their similarity.

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