How do you change keys? This topic is large enough for its own book, but the title The Everything® Harmonic Modulation Book just didn't seem to flow, so it will get a section here. Modulation is simply the art of shifting the tonal center to another key and staying there. What do you know about tonal centers? Essentially, they involve chords and melodies that define certain keys. Most importantly, dominant V chords and tonic I chords are the basic ingredients.
Secondary chords provide a temporary tonal shift. But if you simply held on to secondary chords for long enough, you could shift the tonal center to another key. You could finally modulate.
The simplest way to change keys is to go to a key that is spelled very closely to the key you are in. The rule of thumb is simple: The fewer notes you have to shift, the easier your job is. Start to look at the related keys.
Related keys share notes in common with one another. The more notes they share, the more closely related they are. Review the key circle in FIGURE 12.13 for a second.
FIGURE 12.13 The Circle of Keys
You are in C (an old favorite). The closest related key would be one key to the right or one key to the left, so G and F are keys that you can move into easily. As you start to lose notes in common, it becomes more difficult to slip into a new key. Nothing's impossible, but typically, movements are by fifths, either up to G or down to F, if you start in C.
When you throw in a secondary dominant, you alter a key's landscape by adding a chromatic tone. In these situations, that chromatic tone always goes away. What if you stuck with it? What if you had a section of music that you kept analyzing V/V, V and it never really came back to I? You may have just stumbled onto a modulation.
Here's an example shown in FIGURE 12.14. Start out in C and end up in G. This will be a fairly long progression because you want to set up the idea of the key change and establish the new tonic/dominant relationship so that it sticks.
FIGURE 12.14 Simple Harmonic Modulation
As you can see and hear, you started in one key and ended up in another. You achieved this with two devices. The first is a secondary dominant to the new key. Your goal was to move to the key of V (G major). To do so, V needs to be in the new key (V of G is D7), so you made sure to do that. The minute the V/V showed up, you had an F# in the key. The trick is not to let it go back to F so you did the progression again to solidify the sound of the new key. The other way that this is accomplished is with common chords. For example, to change keys, you need to think in the new key for a second. A I–IV–V progression in any key is pretty strong. You can pull off that progression by using common chords. I–IV–V in the key of G is G–C–D. In the key of C, you have C and G chords already. The only addition is the D, which you get via the secondary dominant chord (V/V). The real trick is not making the G chord a G7. G7 would pull back to C; in FIGURE 12.14, it's kept a triad. Common chords can go further in helping you establish a new key. I–IV–V is not the only progression, as you already know. Look at other common chords. (Notice how you can analyze FIGURE 12.14 in both keys? The analysis is provided for you in C and G. It makes much more sense to look at the second line in G.)
Whenever you are thinking about modulating to a new key, it's nice to know what chords the two keys share; these chords are easy to use effectively. Use the key of C and F this time and look at how you might modulate. The V/V is never a common chord; you always have to change the key, but you have a bunch of other chords that do work. The diatonic triads of C and F major are shown in FIGURE 12.15.
FIGURE 12.15 Chords in C and F
You see a bunch of chords in both keys—C, Dm, F, and Am. In the key of F, those chords are V, vi, I, and iii respectively. So, you do have a V/V chord in this case (it's just not a C7 chord), which you need to fix with a chromatic note. In the key of F, the vi chord is important. What you are missing is a predominant chord, either ii or IV. Neither of those chords is common, but once you've done the whole secondary dominant (or diminished) thing, the next progression after the cadence can continue on as if it's in the new key. The G minor chord you're going to add won't sound odd, because you've already introduced the chromatic tone (B) to the key; it will actually sound as if it belongs to the key of F (see figure 12.16).
FIGURE 12.16 Common Chord Modulation
The way to make a secondary dominant not feel secondary is to not turn back to the old key at all, keep going in the key of F and use typical, diatonic progressions for that key. As you keep writing in the new key, the listener will forget about the key of C since you have tonic-sized the F chord so many times it sounds as though you have modulated, and you have.
Modulation is a big topic with some very simple rules. You know how harmony works, and you know that to move you have to shift the harmony to the new key. The trick is to analyze some music, especially classical music (because of the common modulations), to get used to seeing exactly how it's done.
Just a word of warning: Sometimes the hardest part about modulation is simply knowing a modulation when you see it. As soon as you see chords that don't make sense in the original key, that is a clear sign that you may not be in that key anymore. Look for patterns in other keys. If you can fit the mystery progression into another key, chances are that's exactly where you are. One last thing: You can't modulate without a chromatic note. On the other hand, chromatic notes do not always signal movement into other keys. They could be slight diversions and resolve. Either way, look for the signposts, and most of all, listen. If a chord sounds like a I, it probably is.
ETUDE 12.1 Etude One
Realize the secondary dominant chords from the key and Roman numerals below
ETUDE 12.2 Etude Two
Realize the secondary diminished chords from the key and Roman numerals below
ETUDE 12.3 Etude Three
Realize the borrowed chords from the key and Roman numerals below
ETUDE 12.4 Etude Four
The following example modulates. Indicate the start and ending keys and circle the first chord in the new key.
ETUDE 12.5 Etude Five
Using the space provided, write down the chords that are shared in the key of A and E major