C#7b5 Piano Chord

Piano Diagram of C#7b5 in Root Position

C#7b5 is a dominant seventh chord with a flat 5th built on the C# major scale. This chord consists of the root note C#, the major third E#, the diminished fifth G, and the minor seventh B. The flat fifth creates a distinct dissonance so it can be used as a substitute for dominant chords only in specific musical contexts. If you keep reading, you will learn more about the music theory that underpins this chord.

 

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Structure of C#7b5

 

Fingers Position

 

How to play a C#7b5

Play the root note C# with your left hand. Then, with your right hand, play the notes B (minor 7th), E# (equivalent to a natural F, major 3rd), and G (diminished 5th).

C# + B, E#, G

Omitting the root on your right hand, you can play also one of the three inversions of the chord.

 

C#7b5 Chord Inversions

 

The C#7b5 chord has a total of 3 inversions:

 Piano Keyboard Diagrams

 

C#7b5 Chord Equivalencies

If you take a 7b5 chord, you can find another 7b5 chord that has the same notes in it by either going up three steps from the root note or going down three steps from the root note.

For example, C# is the root note of C#7b5 (C#, E#, G, B), so if you go up three steps from C#, you get to F_x. Therefore, F_x7b5 (F_x, A_x, C#, E#) has the same notes as C#7b5. The same thing happens going down three steps: you get to a G, which is the enharmonic equivalent of F_x.

C#7b5 = F_x7b5 = G7b5

The reason why going up three steps or going down three steps leads you to a chord with the same notes is because the interval between the root note and the diminished fifth is called a tritone. This interval is halfway between the octave and divides it into two equal parts. Therefore, going up three steps or going down three steps takes you to the same note that is a tritone away from the starting note.

So, the C#7b5 chord is equivalent to F_x7b5 and G7b5 because they all have the same notes in them, even though they have different names.

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Music Theory and Harmony of C#7b5

 

Dominant 7b5 chords are often used as transitional chords to add an extra layer of tension to a dominant 7th chord and prepare for the resolution to the tonic. The C#7b5 chord can substitute or enhance the C#7 chord, commonly on the V degree in a minor key, but also on the III degree, and occasionally on other degrees as a secondary dominant chord.

Before examining the most common use of this chord, let’s learn how to build it.

 

Building the C#7b5 Chord: Different Approaches

 

Starting from the C# Major Scale:

To form a 7b5 chord, you combine the root, the major 3rd, the diminished 5th, and the minor 7th from a major scale.

 

 

 

To create a C#7b5 chord, apply the formula R, 3, d5, m7 in the following manner:

1. Begin with the Root note, C#.
2. Select the major 3rd interval, which is E#.
3. Add the 5th interval, which is G# then lower it by half step to get the diminished 5th, G.
4. Add the minor 7th interval, B.

By following this simple formula, you can create a 7b5 chord from any major scale.

 

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by Combining Intervals:

One method to create a 7b5 chord is by combining specific intervals – a major 3rd, a major 2nd, and a major 3rd.

3 + 2 + 3 = 7b5 Chords

For example, to build a C#7b5 chord:

• we start with the root note C#.
• We then add a major 3rd interval, which is four half-steps up from the root, to get E#.
• Next, we add a major 2nd interval, which is two half-steps (a whole tone) up from E#, to get G.
• Finally, we add a major 3rd interval, which is four half-steps up from G, to get B.

Together, these intervals form the C#7b5 chord.

 

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How to Use C#7b5 in a Chord Progression

 

The C#7b5 can work as a substitute or as a passing chord to a C#7 that can be found in major and natural minor scales. However, note that it’s a non-diatonic chord due to the presence of the diminished 5th.

These tables show the harmonized major and natural minor scales where you can find a C#7 or use it in place of other chords.

 

Most common uses of C#7b5

 

C#7b5 in F# Major and F# minor

The C#7b5 chord is commonly used as a dominant chord. In the key of F# major, the C#7b5 chord can be used as the V7 chord, which leads back to the I chord (F# major).

• Substitute or Passing Chord to the Dominant chord in F# Major.

 

C#7b5 as Substitute for C#m7

The C#7 chord derived from the harmonic minor scale is commonly used to replace a C#m7 chord in the key of F# minor. In some cases, the C#7b5 chord can also be used instead of the C#7 chord.

• Substitute or Passing Chord to the Dominant chord in F# minor.

 

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C#7b5 in a I – III⁷ Progression

The C#7b5 chord can serve as a substitute for the III chord in a I-III⁷ chord progression that typically features a C# minor chord. In the chord progression represented by the chords A Maj7 and C#7, the C#7b5 chord can replace the expected C# minor chord.

• Substitute or Passing Chord to the Mediant chord in A Major.

 

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C#7b5 in D# minor

The C#7b5 chord in the D# minor scale could function as a leading tone chord, resolving to the D# minor chord.

• Substitute or Passing Chord to the Leading Tone chord in D# minor.

 

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C#7b5 as Substitute for a Secondary Dominant 7th chord

A secondary dominant is a chord that doesn’t belong to the main key of a song. Instead, it’s used to create a strong pull or tension toward a different chord that does belong to the main key. In Western music, the fifth note of the scale is known for its dominant function, creating tension that typically resolves to the first note of the scale. A secondary dominant serves a similar purpose but directs that tension towards a different chord, briefly taking the music away from the main key.

As an example, in the key of B major, the F#7 chord (which is the V chord) naturally leads back to B Maj7. Now, if you insert an additional chord between B Maj7 and F#7, and this new chord strongly pulls toward F#7, it becomes a secondary dominant chord. For instance, if you introduce a C#7 chord in this sequence, it creates that pull toward F#7 because C#7 is the V chord in the key of F#.

| B Maj7 | F#7 | B Maj7 |

⇒

| B Maj7 | C#7 | F#7 | B Maj7 |

To spice up a harmonic progression, you can switch out or combine the standard C#7 chord with the C#7b5 chord. This alteration or inclusion can bring in more tension and complexity to the progression.

| B Maj7 | F#7 | B Maj7 |

⇒

| B Maj7 | C#7/C#7b5 | F#7 | B Maj7 |

 

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C#7b5 Chord in Major and minor Keys

 

C#7b5 as Dominant Chord in F# Major

In the key of F# major, the C#7 chord serves as the dominant chord. However, you can opt to use the C#7b5 chord instead of or in combination with the C#7 chord. Here’s how you can approach it:

 

C#7b5 Chord Progressions as V degree

To get a better understanding of how C#7b5 works alongside the dominant chord, try playing these chord progressions. Start by playing a C#7b5 chord for half a measure, followed by a C#7 chord. This descending tension creates a pleasing sound, especially in the context of the F# Major key.

ii V I

 

I IV V

 

 I V vi IV

 

I IV vi V

 

 I IV ii V iii vi ii V

 

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C#7b5 as Dominant Chord in F# minor

C#7 can be found also on the V degree of the F# harmonic and melodic minor scales. It’s very common to use this chord in combination with chords built on the natural minor scale or to substitute it for the C#m7 chord that is present in the natural minor scale. In some contexts, we could use a C#7b5 instead of a C#7 in this position.

C#7b5 as V degree on minor Scale – Chord Progressions

Try playing these chord progressions to get an idea of how C#7b5 functions as the subdominant (V degree) in the key of F# minor. I recommend playing a C#7 chord within the same measure as the C#7b5 chord, as it adds a sense of harmonic movement to the progression.

 

ii V⁷ i

 

i iv V⁷

 

i iv VI V⁷

 

i VI V⁷ iv

 

Circle Progression

 

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C#7b5 as III⁷ Degree in A Major

This is a very common substitution of dominant chords in place of minor chords. In the case of C#7, we are in A major since the minor chord we are going to substitute is on the iii degree of the scale:

 

C#7b5 as III7 degree – Chord Progressions

Try playing these chord progressions to get an idea of how C#7b5 functions in this position. To understand why this substitution is possible, I suggest checking out some of the posts related to dominant 7th chords. There are different interpretations of this substitution, so it can be helpful to explore them to fully understand its potential use.

 

I III⁷ vi

 

I III⁷ VI⁷ ii

 

I III⁷ IV VI⁷ ii V iii/biii^ø ii/V

 

“All of me” Progression