B Diminished
So we talked about all the diatonic C Major chords except for B Diminished. Time to cover it now.
Diminished Chords are comprised of a root, its minor third, and its diminished 5th. The distance between the minor third and the diminished fifth is another minor third, so the chord is composed of 2 minor thirds and 1 diminished fifth (and their inverses).
Contents
PreReqs
Open Position B Diminished Triad
| Root Pos. |
|---|
F ||i|-|-|-| D ||-|-|p|-| ||-|-|-|-| F ||-|-|r|-| B ||-|m|-|-| ||-|-|-|-| |
You'll need to use your ring finger to mute the 3rd string when you strum this chord, so you don't hear the open G string. Diminished triads tend to have pretty nasty shapes, and even vanilla B dim is no different. If it's difficult, you can drop the high F with the index finger.
Harmonic Function: Leading Chord
B dim is diatonic to the key of C Major, using its 7th scale degree as the root note. Thus, it is called the vii or vii° chord. The ° indicates diminished, but you have to be careful - we are dealing with the diminished triad here, not the diminished seventh. The Diminished 7th chord has two variations - half and full. Half is indicated with a slash through the ° symbol. Where the ° symbol cannot be made, such as on a standard keyboard, or to avoid ambiguity, you can use "dim" (ex. Bdim) to indicate the diminished quality of the chord.
The vii chord is called the Leading Chord. Harmonically, it has a dominant function.
C F/C B° C I IV vii° I E--0------1------1------0------ B--1------1------3------1------ G--0------2------x------0------ D--2------3------3------2------ A--3------3------2------3------ E------------------------------
Full Circle Progression
C F B° Em Am Dm G C I IV vii° iii vi ii V I E-0---1---1----0---0---1---3---0-- B-1---1---3----0---1---3---3---1-- G-0---2---x----0---2---2---0---0-- D-2---3---3----2---2---0---0---2-- A-3-------2----2---0-------2---3-- E--------------0-----------3------
Now that we know the vii° chord, we can play the full circle progression in the key of C Major.
Diminished Fifth Interval
The vii° chord is the only diatonic chord in any major key to contain the diminished 5th interval. Remember that the most harmonic interval (other than an octave) is the perfect fifth, represented by the simple ratio of 3:2. By contrast, the diminished 5th has a ratio is 7:5. Let's see all the intervals:
| Interval Name | Ratio |
|---|---|
| m2 | 16:15 |
| M2 | 9:8 |
| m3 | 6:5 |
| M3 | 5:4 |
| P4 | 4:3 |
| d5 | 7:5 |
| P5 | 3:2 |
| m6 | 8:5 |
| M6 | 5:3 |
| m7 | 16:9 |
| M7 | 15:8 |
As you notice, the intervals closest to the root note or octave feature the highest numbers on their ratios and have the largest least common multiples. Yet, the d5 is a major departure from the general trend. As it serves as the replacement of the P5 in this chord, this immediately makes the chord quite dissonant.
It's quite apparent when playing the B dim chord. This means the vii° chord not only has tension in the context of the tonality and its placement inside a progression, but it is also quite dissonant and tense in and of itself. Typically, we don't see diminished triads as frequently as 7th or other extended chords. Its half diminished (diatonic to the major, natural minor, and harmonic minor scales) variety actually adds consonance.