Piano Diagram of Bbm7b5 in Root Position
The Bbm7b5 chord, also known as a half-diminished chord, is a minor dominant seventh chord with a flat 5th built on the Bb major scale. This chord consists of the root note Bb, the minor third Db, the diminished fifth Fb, and the minor seventh Ab.
Structure of Bbm7b5
Notes |
|---|
| Bb, Db, Fb, Ab |
Intervals |
|---|
| R, m3, d5, m7 |
Bbm7b5 Chord Inversions
The Bbm7b5 chord has a total of 3 inversions:
| Root Position: | Bb | Db | Fb | Ab |
| 1st Inversion: | Db | Fb | Ab | Bb |
| 2nd Inversion: | Fb | Ab | Bb | Db |
| 3rd Inversion: | Ab | Bb | Db | Fb |
Piano Keyboard Diagrams
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- Bbm7b5 Chord – 1st Inversion
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- Bbm7b5 Chord – 2nd Inversion
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- Bbm7b5 Chord – 3rd Inversion
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- Bbm7b5 Chord – Root Position
Bbm7b5 Chord Equivalencies
When you invert a half-diminished chord to its first inversion, it becomes equivalent to a minor 6th chord built on its minor 3rd.
Let’s take the Bbm7b5 chord which consists of the notes Bb, Db, Fb, Ab: its first inversion is Db, Fb, Ab, Bb, which is actually a Dbm6 chord.
1st Inversion of Bbm7b5 = Dbm6
Understanding the equivalencies of chords can be beneficial when playing or composing music. It can also help in analyzing and understanding the harmonic structure of a piece of music.
Music Theory and Harmony of Bbm7b5
Bbm7b5 is considered a half-diminished chord, which means it has a diminished fifth and a minor seventh interval. This chord can be used as a substitute for other chords, such as a dominant seventh chord or a minor chord.
In jazz and other styles of music, Bbm7b5 is often used as a passing chord or as part of a ii-V-I progression. It can add tension and interest to a musical passage, and can also be used as a starting point for improvisation.
Before examining the most common use of this chord, let’s learn how to build it.
Building the Bbm7b5 Chord: Different Approaches
Starting from the Bb Major Scale:
To form a minor 7b5 chord, you would typically include the root note, minor third, diminished fifth, and minor seventh from a minor scale.
However, when teaching this concept, it can be more effective to demonstrate its construction using a major scale. This is because a major scale better illustrates the relationship between intervals and their respective qualities.
So let’s take the Bb major scale:
Bb Major Scale
Bb Major scale – Keyless Notation
To create a Bbm7b5 chord, apply the formula R, m3, d5, m7 in the following manner:
- Begin with the Root note, Bb.
- Select the third interval, which is D. Then, subtract a half step to obtain the minor 3rd, Db.
- Select the 5th interval, which is F then lower it by half step to get the diminished 5th, Fb (E).
- Pick the 7th interval A, then lower it by a half step to get the minor 7th, Ab.
By following this simple formula, you can create a minor 7b5 chord from any major scale.
by Combining Intervals:
One method to create a Bbm7b5 chord is by combining specific intervals – a minor 3rd, another minor 3rd, and a major 3rd.
m3 + m3 + 3 = m7b5 Chords
For example, to build a Bbm7b5 chord:
- we start with the root note Bb.
- We then add a minor 3rd interval, which is three half-steps up from the root, to get Db.
- Next, we add another minor 3rd interval, which is three half-steps up from Db, to get E.
- Finally, we add a major 3rd interval, which is four half-steps up from E, to get Ab.
Together, these intervals form the Bbm7b5 chord.
How to Use Bbm7b5 in a Chord Progression
The Bbm7b5 chord is frequently used in ii-V-I progressions, where it functions as the ii chord. However, due to its versatile nature, it can also be used in various other musical contexts, such as:
- on natural minor and Major keys
- as a substitute for dominant 7th chords
- as a substitute for minor chords
Most common uses of Bbm7b5
The Bbm7b5 chord is found on the second scale degree (II) in the Ab natural minor scale and on the seventh scale degree (VII) in the Cb major scale. However, both of these keys are considered theoretical due to the high number of accidentals they involve. For this reason, it is more practical to use their enharmonic equivalent keys. The enharmonic equivalent of Bbm7b5, which is A#m7b5, is often preferred in this context.
| Minor Scales | i | ii | III | iv | v | VI | VII |
|---|---|---|---|---|---|---|---|
| Ab | Ab min7 | Bbm7b5 | Cb Maj7 | Db min7 | Eb min7 | Fb Maj7 | Gb7 |
- Supertonic chord in Ab minor
| Major Scales | I | ii | iii | IV | V | vi | vii |
|---|---|---|---|---|---|---|---|
| Cb | Cb Maj7 | Db min7 | Eb min7 | Fb Maj7 | Gb7 | Ab min7 | Bbm7b5 |
- Leading tone chord in B Major
Bbm7b5 as a Substitute for Dominant 7th Chords
Minor 7th flat 5th chords can replace dominant 7th chords when they share some of the same notes. A general rule of thumb when it comes to chord substitutions is that if the substitute chord contains at least the 3rd and 7th notes of the original chord, it’s often a viable option for substitution.
C7 ⇔ Bbm7b5
Gb7 ⇔ Bbm7b5
In this case, the Bbm7b5 chord (Bb, Db, Fb, Ab) can serve as a substitute for C7 (C, E, G, Bb) and Gb7 (Gb, Bb, Db, Fb) due to their shared notes. Specifically, Bbm7b5 shares the 7th and 3rd notes of C7 (which are Bb and E, respectively), as well as the 3rd and 7th notes of Gb7 (which are Bb and Fb).
Rootless dominant 9th Chord Substitution
It’s worth noting that the substitution of Gb7 with Bbm7b5 can also be viewed as a rootless dominant 9th chord substitution. This is because Bbm7b5 contains the same essential notes as the Gb9 chord except the root note.
Gb9 = Gb (Bb, Db, Fb, Ab)
Bbm7b5 = Bb, Db, Fb, Ab
Bbm7b5 as a Substitute for minor Chords
To replace a minor chord with an m7b5, build the m7b5 by taking the note three semitones lower than the original minor chord. So, in the case of a Db minor chord, the m7b5 chord would be built three half-steps lower than the root note Db.
On the ii Degree
| ii | V | I |
| Db min7 | Gb7 | Cb Maj7 |
| Become | ||
| Bbm7b5 | Gb7 | Cb Maj7 |
You can apply this substitution to a ii V I progression that has a Db minor chord on the ii degree by replacing it with a Bbm7b5 chord.
On the IV Degree
I IV iv I
| I | IV | iv | I |
| Ab Maj7 | Db Maj7 | Db min7 | Ab Maj7 |
| Become | |||
| Ab Maj7 | Db Maj7 | Bbm7b5 | Ab Maj7 |
Bbm7b5 Chord Function in Major and Minor Keys
Understanding Scale Degrees
When we form chords from a scale, each note in the scale is given a specific degree that reflects its position within the scale. The degree of a note in a scale determines its function and the role it plays in the overall harmony of the music.
- Starting with the first degree of the scale, we have the Tonic chord. This chord serves as the foundation of the scale, providing a stable tonal center for the music. It’s like the “home base” of the music, and all melodies and harmonies are anchored to this chord.
- Moving on to the second degree, we have the Supertonic. This degree acts as a transitional note between the tonic and other notes in the scale, creating a sense of movement and flow in the melody or harmony.
- The third degree is the Mediant, which is located halfway between the tonic and dominant notes. This degree helps to establish whether the scale is major or minor and plays a critical role in determining the mood and emotional impact of the music.
- The fourth degree is the Subdominant, which complements the dominant and adds tension and resolution to the music. It creates a push-pull effect that keeps the listener engaged and interested.
- The fifth degree is the Dominant, which generates tension and a sense of expectation. It often acts as the climax of a musical phrase or section and is resolved by returning to the tonic.
- The sixth degree is the Submediant, which provides a sense of stability and restfulness to the music. It’s often used as a transition between the dominant and tonic, creating a feeling of calm and relaxation.
- Finally, we have the seventh degree, the Leading tone. This degree produces a strong sense of tension and a desire to resolve to the tonic. It’s often used to create a sense of resolution and completion in the melody or harmony.
Bbm7b5 as Supertonic Chord in Ab Minor
In Ab minor, the Bb half-diminished chord functions as the supertonic on the second scale degree. It commonly serves as a passing chord to create movement within a progression. It could be easier to refer to the enharmonic equivalent key of Ab minor which is G# minor and use the A#m7b5 chord instead of Bbm7b5.
| i | ii | III | iv | v | VI | VII |
| Ab min7 | Bbm7b5 | Cb Maj7 | Db min7 | Eb min7 | Fb Maj7 | Gb7 |
Bbm7b5 Chord Progressions as ii degree
Here are some examples of chord progressions that feature the Bb half-diminished as the supertonic chord.
It’s a common practice to substitute the minor 7th chord found on the fifth degree of the natural minor scale with a dominant chord built on the harmonic minor scale. This is why you may see an Eb7 chord used instead of an Eb min7 chord in some of these progressions.
ii iv V7 i
| ii | iv | V7 | i |
| Bbm7b5 | Db min7 | Eb7 | Ab min7 |
iv ii i
| iv | ii | i |
| Db min7 | Bbm7b5 | Ab min7 |
VII ii i
| VII | ii | i |
| Gb7 | Bbm7b5 | Ab min7 |
ii V7 i
| ii | V7 | i |
| Bbm7b5 | Eb7 | Ab min7 |
Circle Progression
| i | iv | VII | III | VI | ii | V7 | i |
| Ab min7 | Db min7 | Gb7 | Cb Maj7 | Fb Maj7 | Bbm7b5 | Eb7 | Ab min7 |
Bbm7b5 as Leading Tone Chord in Cb Major
In Cb major, the Bbm7b5 chord is the leading tone chord built on the seventh degree of the scale. However, Cb major is a theoretical key and it’s more practical to refer to its enharmonic equivalent key, B major where is present the A#m7b5 chord.
| I | ii | iii | IV | V | vi | vii |
| Cb Maj7 | Db min7 | Eb min7 | Fb Maj7 | Gb7 | Ab min7 | Bbm7b5 |
Bbm7b5 Chord Progressions as vii degree
The following chord progressions feature the Bbm7b5 chord as the leading tone:
V vii I
| V | vii | I |
| Gb7 | Bbm7b5 | Cb Maj7 |
I IV vii iii vi ii V I
| I | IV | vii | iii | vi | ii | V | I |
| Cb Maj7 | Fb Maj7 | Bbm7b5 | Eb min7 | Ab min7 | Db min7 | Gb7 | Cb Maj7 |
Bbm7b5 as Substitute for C7
Bbm7b5 shares the 7th and 3rd notes of C7 so it’s possible to use a Bbm7b5 in place of a C7 on the V degree. This is a common substitution used in jazz music and can add some interesting harmonic color to a progression.
| I | ii | iii | IV | V | vi | vii |
| F Maj7 | G min7 | A min7 | Bb Maj7 | C7 ⇒ Bbm7b5 | D min7 | Em7b5 |
ii V I
| ii | V | I |
| G min7 | Bbm7b5 | C7 | F Maj7 |
I IV ii V iii vi ii V
| I | IV | ii | V | iii | vi | ii | V |
| F Maj7 | Bb Maj7 | G min7 | C7 | Bbm7b5 | A min7 | Dmin7 | G min7 | C7 |
You can play the Bbm7b5 chord by itself, or use it in combination with a C7 chord, either before or after the Bbm7b5. This will allow you to explore the different tonal colors and tensions that each progression creates, and help you develop a stronger sense of how these chords can be used effectively in your musical compositions or improvisations.
Bbm7b5 as Substitute for Gb7
Bbm7b5 shares the 3rd and 7th notes of Gb7 (which are Bb and Fb). This means that it is possible to use Bbm7b5 as a substitute for Gb7. As before, it is more convenient to refer to the key of B major instead of the theoretical key of Cb major.
| I | ii | iii | IV | V | vi | vii |
| Cb Maj7 | Db min7 | Eb min7 | Fb Maj7 | Gb7 ⇒ Bbm7b5 | Ab min7 | Bbm7b5 |
ii V I
| ii | V | I |
| Db min7 | Bbm7b5 | Gb7 | Cb Maj7 |
I IV V
| I | IV | V |
| Cb Maj7 | Fb Maj7 | Bbm7b5 | Gb7 |
I V vi IV
| I | V | vi | IV |
| Cb Maj7 | Gb7 | Bbm7b5 | Ab min7 | Fb Maj7 |
Using the Bbm7b5 chord by itself or in combination with a Gb7 chord can create different tonal colors and tensions. Experimenting with these progressions can help develop a stronger understanding of how to use these chords effectively in your musical compositions or improvisations.
Alternative Bbm7b5 Nomenclature
- Bbø
- Bb∅
- Sibø
- Bbm7b5
- Bbm7°5
- Bbm7b5
- Bbm7/b5
- Bbm7(-5)
- Bbm7(b5)
- Bb 1/2dim
- Bb 1/2dim7
- Bbm7 Flat 5
- Bb minor 7th b5
- Bb half-diminished
- Bb minor seventh flat fifth
Conclusion
The chord progressions and examples presented in this post provide a comprehensive overview of the most common uses of the Bbm7b5 chord. It’s important to note, however, that many advanced harmony-related topics could not be included due to space constraints. These topics include chord progressions built on harmonic and melodic scales, modal scales, hidden tonality, secondary dominants and other chord substitutions, non-functional harmony and atonal music, modal interchange and borrowed chords, voice leading and counterpoint, chromatisms, jazz harmony…I mean, music theory is a huge topic!
Although I couldn’t cover all of these topics in my post, I encourage readers to continue exploring these areas in their own study and research. By expanding your knowledge in these advanced areas of music theory, you can gain a deeper understanding of the harmonic possibilities that exist beyond the basics presented here.