Definition
The diminished chord can be used in many ways and there are many questions about how to apply them. One of the applications is to use it as a passage chord to give harmony a color. It can also be used in modulations (changes of tonalities, chromatic approximations, the substitution of the dominant, etc.). Let us first understand how we can build them and then we will see some examples of how to use them.
The diminished term means to decrease and is usually applied in music scales when we have a perfect or minor interval that has been lowered in a semitone. We have at least three types of diminished chords.
Diminished Triad
The first type is the diminished triad, which is built when we lower the perfect fifth in a minor chord. For example, the C minor chord (Cm) is formed by the tonic (C), the minor third (Eb), and the perfect fifth (G). So, if we lower the fifth of this chord in one semitone, then we have the diminished triad of C represented by the chord symbol C5b (formed by the notes C, Eb, Gb). We can define a formula to build this chord as 1, 3b, 5b, where the numbers represent the degrees of the major scale Then 1 is the tonic, 3 is the major third and in our case 3b is the minor third (lower major third in halftone), 5 is the perfect fifth, in our case 5b is the diminished fifth.
Half Diminished Chord
The second type is the half-diminished chord that starts with the diminished triad and is built by adding the minor seventh also called the dominant seventh to it. The chord symbol for the C half-diminished chord is C75b or CØ. The formula to build this chord is 1,3b, 5b, 7 (tonic, minor third, diminished fifth, and dominant seventh or minor seventh), which in this example is formed by the notes C, Eb, Gb, Bb. You may have noted that we did not write the minor seventh as 7b but as 7. This is just to have the same symbol used in the chord symbol, so we don’t get confused. We write major seventh as 7M and minor or dominant seventh as 7. In the C major scale, B is the major seventh and Bb is the minor or dominant seventh.
Diminished chord
The third type is the diminished chord and the building formula is 1,3b, 5b, 7b. We already know that 7 is the minor seventh (dominant seventh), so 7b is the diminished seventh. In summary, in order to have the diminished chord for a given major dominant (seventh) chord, we should lower half a tone on the third, halftone in the perfect fifth, and a halftone in the minor seventh, thus becoming tonic, minor third, diminished fifth and diminished seventh. In our example, the chord notes are C, Eb, Gb, Bbb (sounds like A) and the chord symbol is C°.
Examples
Let’s see some examples of diminished chords applying the formula in different tones:
C
D°: Starting with the major seventh chord: D, F #, A, Cb and lowering the third, the fifth, and the seventh we have: D, F, Ab,
To summarize, we have
| Chord | Formula | Chord Symbols |
| Diminished triad | 1,3b, 5b | C5b, F # 5b, Eb5b |
| Half diminished | 1,3b, 5b, 7 | CØ, AbØ, F #Ø |
| diminished | 1,3b, 5b, 7b | C°, G°, Ab° |
Diminished chords create tension in the music. In harmony, we say that it needs resolution because the sound stays “in the air” waiting for something to happen. Tension generates an expectation. It’s like throwing a ball up and waiting for it to come back and hit the ground. The moment the ball returns is our resolution.
When we set the major scale chord progression, the half-diminished chord appears in the seventh degree. The diminished chords appear in the second degree of the minor harmonic scale chord progressions. The half-diminished chords also appear in the sixth degree of the minor harmonic scale
But the basic question is: How and when can I use them? Let’s check out some typical uses of these chords:
How to use
Substitute of dominant
Every
Examples:
C7: formed by the notes C, E, G, Bb
C #°: formed by the notes C #, E, G, Bb
C7 can be replaced by C #°
In the following chord progression, G7 can be replaced by G #°
ǁ Dm7| G7| C7Mǁ can be replaced by ǁDm7|G #° |C7mǁ
Chord of passage:
The diminished chord can be used as a passage chord. When there is, for example, the distance of a tone between one chord and another of a progression, it can be filled with a diminutive chord.
Examples:
ǁ I (1 tone) ii (1 tone) iii (half tone) IV (1 tone) V (1 tone) vi (1 tone) viiǁ
ǁ C Dm ǁ
As between C and Dm there is one tone, we can insert a passingb diminished chord between them as following.
ǁ C C#° Dm ǁ
Considering the whole scale chord progression we have:
ǁ C Dm Em F G Am Bm ǁ
ǁ C C # ° Dm Eb ° Em F F ## G G # ° Am Bb ° Bm ǁ
