Tritonic chords are chords that have the augmented fourth or diminished fifth (aka – “tritone”) as an intervallic component. The earliest chromatic dissonant interval to be discovered was the augmented fourth/diminished fifth.
The tritone consists of three adjacent whole tone progressions (whole steps) from any given note but can be formed by raising the fourth scale step (to yield an augmented fourth) or lowering the fifth scale step (to yield a diminished fifth).
In the key of C major, raising F (the fourth scale step) to F♯:
…or lowering G (the fifth scale step) to G♭:
…will both yield the tritone (three adjacent wholetone progressions or whole steps).
C-D, D-E, E-F♯.
C-D, D-E, E-G♭.
There was a time when the tritone was considered the devil in music because of its extreme dissonance. Owing to this dissonance, chords that contain the tritone are associated with instability, tension, and unpleasantness and are generally referred to as tritonic chords.
Leading Note Triad
The seventh degree of the major and harmonic minor scales are called the leading note because of the semitone progression (half step) in between them.
C major scale
C harmonic minor scale
The pure (or natural) minor scale is not used in harmony because of this shortcoming (doesn’t have leading note).
The seventh degree of both scales is B. If a tertian triad is built off the seventh degree (B) of each of the scales, the outcome will be a diminished triad.
The triad of the seventh degree is tritonic. There are three adjacent whole tone progressions (whole steps) from B to F and can be specifically described as a diminished fifth because the natural F is a semitone lower than F♯ (which is the fifth scale tone of the B major scale):
Chord Formation of Diminished Triads
Before we go any further, let’s take a couple of minutes to review how to form diminished triads in ALL keys.
#1 – Using Major Triads
If you are already familiar with major triads in all keys, then formation of diminished triads will be a piece of cake. If you take a closer look at B major and diminished triads, you’ll be able to derive the intervallic formula of the diminished triad.
The third and fifth chord tones of the B diminished triad (D and F respectively) are a semitone lower than the third and fifth of the B major chord (D♯ and F♯). This simply means that lowering the third and fifth chord tones of any major triad will yield a diminished triad. Below are all diminished chords arranged chromatically from C to C.
*Pardon my enharmonic spelling of E♭ diminished as D♯ diminished.
#2 – Using Intervallic Components
The diminished triad is symmetrical. This means that the diminished triad can be broken down into two identical intervals. Using B diminished as an example:
There are two consecutive intervals: B-D (minor third) and D-F (minor third). Therefore, when two minor intervals are stacked in the manner above, the result of a diminished triad is inevitable. Below are:
1st minor third + 2nd minor third = diminished triad
Feel free to use whichever approach is better for you. You’ll certainly arrive at the same result. The diminished chord is tritonic and so are other chords ranging from the dominant seventh chord to the diminished and half-diminished seventh.
In this post, we’ll explore chord formations of three tritonic seventh chords via the diminished triad (aka – “leading note triad”).
*There are tritonic chords that cannot be formed from the diminished triad and they are intentionally excluded.
Tritonic Chord #1 – Half-Diminished Seventh
The half diminished seventh chord is a tritonic chord. It is the seventh chord of the seventh degree of the major scale. In the key of C, if we stack thirds starting from the seventh degree to encompass the interval of a seventh, we’ll get:
This chord is called a half-diminished seventh because it has a minor seventh instead of a diminished seventh. This chord is closely associated with the minor seventh chord:
Most people describe the half-diminished chord as a minor seventh flat five (min7b5). “What does flat five sound like?” The diminished fifth is formed by the lowering of the fifth degree (technically a “flat five”).
To form a half-diminished seventh chord, play a diminished triad, then add a note that is a major third above the fifth chord tone. For example, C half-diminished seventh chord:
…is formed from C diminished + major third from G♭ (the fifth chord tone):
A half-diminished seventh chord:
…is formed from A diminished + major third from E♭ (the fifth chord tone):
Tritonic Chord #2 – Diminished Seventh
Next on the list of tritonic chords is the diminished seventh chord. It is the seventh chord of the seventh degree of the harmonic minor scale. Using C harmonic minor scale, if we stack thirds on the seventh degree of the scale in such a way that it encompasses the interval of a seventh, we’ll have:
This seventh chord pretty much looks like two diminished triads stacked together:
Owing to the presence of two diminished triads, this seventh chord can be broken down into two mutually exclusive tritones:
That’s why the diminished chord sounds extremely dissonant.
To form a diminished seventh chord, play a diminished triad, then add a note that is a minor third above the fifth chord tone. For example, D diminished seventh chord:
…is formed from D diminished + minor third from A♭ (the fifth chord tone):
A diminished seventh chord:
…is formed from A diminished + minor third from E♭ (the fifth chord tone):
Tritonic Chord #3 – Dominant Seventh
Let’s end this post with the dominant seventh chord. This is the seventh chord of the fifth degree of the major and harmonic minor scales. Using C major or harmonic minor scale, if we stack thirds on the fifth degree of the scale in such a way that it encompasses the interval of a seventh, we’ll have…
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This is the second chord in a 2-5-1 progression. The tritonic content of this chord is what makes it sound tense. There is a minor and major chord on both ends of the 2-5-1 progression. However, in between is the dominant seventh that creates a centripetal pull and energizes the harmonic flow.
To form a dominant seventh chord, form a diminished triad on the third degree of the major scale of any key. For example, D dominant seventh chord:
…is formed from D bass note + diminished triad on F# (the third chord tone):
E dominant seventh chord:
…is formed from E bass note + diminished triad on G# (the third chord tone):
Using all that we’ve covered here, you can get busy learning tritonic chords in ALL keys while I get busy preparing another post on the application of tritonic chords.
See you next time,