Harmonic Alchemy - Face The Diminished

Introduction

I introduced one of the Diminished family, the dim 7th chord, in part 1 of the Harmonic Alchemy series, "Mining for Precious Chords", and elucidated its role as a svelte non-diatonic 'chord substitution'. In this article I will take a much closer look at the 'diminished' sound and its theoretical sources.

Specifications

Diminished chords are so named because of the presence of the following unique intervals i.e. their thirds & 5ths are flat (minor 3rd and diminished 5th respectively). For this reason they are often called 'minor flat 5 chords'. The diminished family includes the following chords: mb5, m7b5, m6b5 (or mbb7b5, -, dim7th), mb9b5, m11b5, mb13b5, m13b5.

Vibe

These intervals create a tense dissonance and peculiar sonority. Pick through the F# mb5 below, letting the intervals ring into one another (novices are too keen to 'strum' a new find and dismiss it outright):

Notice it's strange but appealing vibe. This atmosphere is the playground of modern horror/thriller sound designers and was once where the likes of Bach and Mozart went to seek representation of anguish. Download this informative article (pdf), pages 8-17.

Now play a G major before it and an Em after

The weirdness dissipates as it slots right in, fit for purpose as a leading chord. In this way the dim chord can be used independently for its eldritch qualities, or as a team player.

Source

The natural diatonic source for the diminished triad (R b3 b5) is the Locrian Mode because its tonic triad is diminished i.e. F# Locrian in the key of G or Em is spelled: F# G A B C D E and its tonic triad is F# A C. The interval between F# and A is a b3 and between F# and C is a b5 (also known as a tritone or augmented 4th). Note there is a b3 between the A and C so you could perceive the triad as a pair of b3rds stacked.

The b3, b5 combination also emerges by virtue of the Harmonic Minor scale. Staying in the key of Em, and sharpening D (E F# G A B C D#) reveals 3 more instances of the diminished triad- A Dorian (A C D#), C Lydian (C D# F#) and D# Mixolydian (D# F# A).

Similarly, the E Melodic Minor scale (E F# G A B C# D#) reveals a dim triad on the C# (C# E G). The dim triad above (F# A C) is also a feature of the following scales:

1. F#m Blues: F# A B C Db E
2. F# 1/2 whole diminished: F# G A A# C C# D# E
3. F# whole 1/2 diminished: F# G# A B C D D# E
4. F# Chromatic

Shapes

Here are the shapes of F# dim based on the CAGED system (note: some of these shapes require angled bars):
 

The dim 7th chord mentioned in the intro is a diminished triad chord extended by a 6th or bb7th (F# A C + D#). This extended dim chord also goes by the following monikers e.g. F#mb5 bb7, F#0, F# -. This is also the most common diminished chord. Indeed, most folk aren't aware of the rest of the family so I have prepared a few other extensions taken from the Locrian Mode:

The F#m7b5 is known as a 'half-diminished', which is odd considering it has an authentic diminished triad.

Miscellaneous

Here's a shortcut to a dim7 chord. If you raise the root of a dom 7th you get a dim 7th e.g. raise the F in F7 (F A C D#) to F# (F# A C D#).

In this way you can re-use the common dom7 shapes to produce dim7ths.

A dim7th chord can also be seen as an inversion of a Dom7 b9, e.g.

Refer to my previous Harmonic Alchemy articles to see how this knowledge can be used to inform chord substitutions.

Conclusion

I hope this article has cast the diminished chord in a favourable light and will encourage you to explore its intriguing qualities further.