The most dissonant chord in the major key that is rarely used is the 7-chord and in this lesson I’ll tell you why.
The term dissonant here is used to describe the unpleasantness of the 7-chord and describing the 7-chord as the most dissonant chord in the major key means that the 7-chord is the most unpleasant chord in the major key.
Before I go ahead and tell you why the 7-chord is the most dissonant chord in the major key, let’s invest the next segment into refreshing our minds on the 7-chord in the major key.
A Quick Review On The 7-chord In The Major Key
The chord of the 7th tone of the scale in any key is known as the 7-chord and this is derived from a number system where chords are associated with numbers.
In the number system, every tone of the C major scale:
…is associated with numbers, starting from C which is associated with 1:
C is 1
D is 2
E is 3
F is 4
G is 5
A is 6
B is 7
The 7-chord is the chord of the seventh tone of the C major scale (which is B):
…and can either be a triad or a seventh chord:
Triad (B diminished triad):
Seventh chord (B half-diminished seventh chord):
“How To Find The 7-chord In Any Key…”
Go a half-step below the first tone in any key you’re in and form a diminished triad or a half-diminished seventh chord and you’ll have the 7-chord.
In the key of D major:
…a half-step below D (which is the first tone in the key):
…is C#:
So, C# diminished triad and C# half-diminished seventh chord:
C# diminished triad:
C# half-diminished seventh chord:
…are 7-chord options in the key of D major.
The Dissonance Of The 7-chord — Explained
The major key is populated with common chords and they are either of a major or minor quality: the 1-chord, 2-chord, 3-chord, etc., are all common chords and they are NOT dissonant.
Let’s discuss briefly on common chords.
A Short Note On Common Chords
When the interval between the root and fifth tone of a chord is a perfect fifth, such a chord is said to be a common chord.
In the key of C major:
…where the 1-chord is the C major triad:
…the interval between the root and fifth tone (which are C and G respectively):
…is a perfect fifth interval.
The 7-chord Is Not A Common Chord
The only chord that stands out in the major key is the 7-chord and this is because every other chord is a common chord. A closer look at the B diminished triad:
…which is the 7-chord in the key of C major, you’ll notice that the interval (or distance) between its root and fifth tone (which are B and F respectively):
…is a diminished fifth.
The diminished fifth interval between the root and fifth tone of the 7-chord makes the 7-chord sound unstable, unpleasant, and dissonant.
Final Words
The primary reason why the 7-chord is the most dissonant chord in the major key is because it is NOT a common chord.
The 7-chord is rarely used in the major key and when used, it functions as an incomplete dominant chord and we’ll be looking at the relationship between the 7-chord and the dominant chord in another lesson.
All the best!
