Note: This article is designed for intermediate or advanced musicians who have basic knowledge in music composition and theory. If you find the terminology hard to understand, I recommend studying some basic chord theory first.

 

The correct musical term for changing key is modulation. Changing key is a great way to create contrasts in your music. If done well, a good key change will be the difference between a boring and exciting composition. There are many ways to change key, and this article explains one of them using secondary dominant chords. A chord that contains notes that do not belong to the key that you are working in is called a borrowed chord. A secondary dominant is a type of borrowed chord, and it is always either a fifth or seventh degree chord.

 

For example, D7 is a secondary dominant in C-major. It contains F#, which does not belong to the C-major scale, so therefore D7 is a borrowed chord. In this case the D7 chord is borrowed from the key of G-major, and it is marked V7/V in C-major, because D7 is the dominant chord degree (V7) of G-major, and G is the fifth degree (V) of C-major. In C-major, the other secondary dominant of the fifth degree (G) is F♯-diminished, because it is the seventh degree in G-major. This is marked VII/V.


Secondary dominants in C-major:

 

V7/II = A7                                                 VII/II = C♯-diminished

V7/III = B7                                               VII/III = D♯-diminished

V7/IV = C7                                               VII/IV = E-diminished

V7/V = D7                                                VII/V = F♯-diminished

V7/VI = E7                                               VII/VI = G♯-diminished

V7/VII = F♯7                                          VII/VII = A♯-diminished

 

Using secondary dominants moves you away from the key that you are working in temporarily. For example, we might have a song in C-major that starts with these chords:

 

C | F G | C | C | D7 | G

 

D7 is the secondary dominant that leads to G. However, just using D7 once is not powerful enough to make us feel as though we have changed key. At G, we still feel like it is the dominant of C-major. At this point, we need to add more chords in G-major, so that the key change becomes clear.

 

Let’s start by adding A-minor, the subdominant of G-major. Then adding another G-major chord with D in the bass:

 

C | F G | C | C | D7 | G | Am G/D

 

These two chords are a powerful indicator that we are on our way to G-major.

 

Finally, we can use a cadence to verify the key change. A cadence is a harmonic configuration that creates the sense of resolution. It is a progression of at least two chords that concludes a section of a piece. In this case, it concludes our modulation to G-major. After the chords A-minor and G/D, we can simply add a perfect authentic cadence, which consists of the V7-degree and I-degree chords. The perfect authentic cadence is the strongest type of cadence and often found at structurally defining moments in music. In this case, the perfect authentic cadence consists of D7 and G:

 

C | F G | C | C | D7 | G | Am G/D | D7 G

 

We have now arrived at G-major and our key change is complete. Try playing the chord structure on your instrument, and listen carefully to what the key change sounds like.

 

The example method presented above can be applied using any secondary dominants. Here is a simple formula you can use as a basis for changing key using secondary dominants:

 

Music in original key —> Tonic degree of original key —> Secondary dominant —> Tonic chord of the new key —> Subdominant of new key —> Dominant of new key —> Arrive at new key

 

© Matti Carter 2018

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