Modulation Using Diminished Chord
Using the dominant 7 chord to change keys is one way to do it, but another way is with the diminished chord. An interesting difference between these two methods is the dominant 7 chord is an obvious key change, because if you are playing in the key of D major, then Adom7 is the only dominant chord in that key.... So if you play a Gdom7 to lead to the key of C major, the Gdom7 is an obvious key change because Gdom7 is not in the key of D major. When compared to using the diminished chord, you can actually start off in the key of C major, play a Bdim chord in the key of C major and change keys right into the key of Eb major or Gb major. This is because the diminished 7 chord is actually
four different diminished chords in one. This is explained
here.
Lets take a look at how this can be used for modulation.
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Theoretical Explanation
B diminished chord contains the following notes:
B D and F
You may already know that the B diminished wants to resolve to C major. This is because of the B and F notes, these two notes form a diminished 5th, which is a very unstable interval. The diminished 5th causes “tension” in the diminished chord that wants to be resolved. The rule of thumb is that altered tones want to resolve in the same direction that they were altered, so a diminished interval wants to resolve “downward” and an augmented interval wants to resolve “upwards”.
Let’s see an example:
A perfect 5th interval starting on B consists of B and F#. In a diminished 5th the F# is lowered (flatted) to F, then to resolve it the note must again be lowered to E.... However this doesn’t complete the resolution, the B note also has to be moved up to C (because the
leading tone wants to move up to the tonic). In other words,
the diminished 5th interval leads to the tonic and anytime you have this diminished 5th interval in a chord it will pull towards the tonic. If you were to play these two intervals on a keyboard your hand would be moving “inward” to resolve the diminished 5th.
(For those that don’t have a keyboard, use the picture below for better visualization of the movement in these interval changes.
Virtual Keyboard)
Now play this on the keyboard (or the virtual keyboard) to see the movement and then for those that don’t have a keyboard, play it on the guitar and hear the resolution of these intervals:
B F# to C E
That is the key to the diminished chord’s “tension”.
So how does this allow you to change keys? Well, that’s the fun part the diminished chord just happens to be a rather odd chord in that it can also be used as the diminished chord in other keys because they all contain basically the same notes!
B° = B D F
D° = D F Ab
F° = F Ab B
(The ° symbol stands for “diminished”)
But wait, there is no Ab in the B° chord... So why does this chord work in place of the other diminished chords? This is because if you add the Ab to the B° chord you get a B°7 chord (B full-diminished), so when you use a B° in place of the other chords, it looks like this:
B° = B D F (1, b3, b5)
D°7 = D F B (1, b3, bb7)
F°7 = F B D (1, b5, bb7)
Therefore, the B° will be the same as a D°7 but without the b5, and it will also be the same as the F°7 but without the b3. This is why this chord works in place of these other chords... Which of course leads us up to the B°7 chord, which as you have probably guessed will now contain the exact same notes as the D°7 and F°7 chords.
B°7 = B D F Ab
D°7 = D F Ab B
F°7 = F Ab B D
But now we get to add another chord with the addition of the Ab note... Yep, you guessed it, the Ab°7 chord... But due to the key it is in, we actually have to call this a G#°7 chord (remember that Ab and G# are the same note), you’ll see why in a moment.
G#°7 = G# B D F
So if you are playing in the key of C major, this gives you 3 different keys you can change to by using this one B°7 chord:
Eb major
Gb major
A major
In case you were wondering how the full-diminished 7 chord can be “4 diminished chords in one”, it is because the distance between each note in the chord is a minor 3rd:
B --> D = minor 3rd
D --> F = minor 3rd
F --> G# = minor 3rd
G# --> B = minor 3rd
B --> D = minor 3rd... (etc...)
So to clarify a little more....
Just like the B diminished chord leads to the C chord (tonic), each of the other diminished chords will lead to their respective tonic chords.
B diminished --> C
D diminished --> Eb
F diminished --> Gb
G# diminished --> A
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This btw, is why the G# diminished couldn’t be an Ab diminished chord, because that chord is leading to an A major chord and you have to use all of the letters in any key. But using the Ab instead of G#, there wouldn’t have been any G chords in that key and there would have been two A chords. Even though they are both the same chords (G# and Ab) using the G# is the “correct” way to spell out the chords in the key.
So by looking at this diagram, you can (hopefully) see how each of those chords could resolve to their tonic chord... And you also understand that the B°, D°, F°, and G#° all contain the exact same notes and thus are the exact same chord (just in a different inversion – And for those who don’t know inversions, then that may be a topic for another time
)... If you get both of these concepts then you will have mastered a new technique for changing keys in your songs.
One more thing to notice before we stop is that the Gdom7 and the B° look an awful lot alike...
Gdom7 = G B D F
B° = B D F
No wonder they both have the same pull towards the “tonic”, they contain most of the same notes... Oh and what’s this? They both contain that diminished 5th interval as well... Remember from earlier that the diminished 5th wants to resolve to the tonic? Well, that’s why both the V and the vii° chord have a “pull” towards the tonic. Therefore, these chords can both be used in substitution for the other. Wherever you wanted to play a V chord, you can place a vii° and vice versa to create a little different sound but still keep the same
tendency to resolve to the tonic. Pretty cool huh?
* End Of This Series Back To Main Forum
Also be sure to check out the other misc music theory lessons that are not part of this series and the music theory Q&A thread.