10. Modulations

In the last episodes we talked about cadences and dominant chords.
Basically saying that a chord a Vth degree naturally creates a tension that wants to be resolved by a chord of the Ist degree.

Also saying that this chord of Vth degree can be major in all tonalities, and we can emphasise this tension even more by making this Vth degree chord a dominant 7th chord, with a major third and a minor 7th.

For example, G7, which is a G major chord with a minor 7th, is a great chord to go on either C Major or C minor, because G is the fifth of C.

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And we can use that to make smooth transition between 2 tonalities. Using a G7 to switch between CM and Cm for instance.

Switching from a tonality to another is called a modulation.
But remember that the closer two tonalities are on the circle of fifth, the smoother the transition.

So a transition between CM and Cm, while still very possible, would not be as smooth as a transition between CM and one of its adjacent scales. It's because between CM and Cm there are a lot more notes that are different, a lot more alterations that would make the change more drastic.

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So say I'm in CM and I have this chord progression: CM Am FM.
And then I want to modulate to Dm to have this chord progression: Dm BbM Gm.
We can make the transition smoother by adding a A7 chord just before the Dm, A being the fifth of D.

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And in the same way you could use a C7 chord if you want to go to FM or a D7 if you want to go to GM, for example.

The authentic cadence and the tension a dominant chord creates is really handy to announce where we are going with our chord progression, and therefore, to do modulations.

Of course in music, you don't have to always follow all these rules strictly. In music if it feels right, then it is right, it's your music. Instead of using the authentic cadence to do a modulation you could take advantage of other cadences, like the plagal IV to I for example

But there are other ways to make a smooth transition between two tonalities.

One of them is the harmonic sequence.
A sequence is a pattern that repeats itself, with each iteration offset by a certain interval, usually in only one direction.
The pattern can be melodic, which makes a melodic sequence.
Or the pattern can be a chord, which make a harmonic sequence.

These sequences can be tonal sequences, which means that they are bound to one tonality. In this case some intervals will move a bit, so all the notes used are the notes from the scale of that tonality.

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Or these sequence can be real. Which means that each pattern is an exact transposition of the first one. In this case, the sequence will use notes that are not in the scale we started with.
So we can use that to make our modulations.

So let's make one of those real sequences, in three steps.
Step 1: create a pattern, or a chord, I'll take CM
Step 2: chose an interval and a direction. The most used is probably the descending fifth, so I'll take this one for the example. But ascending fifth and descending third are also rather common.
Step 3: copy your pattern following the direction and the intervals of your choice.

So here that would make CM FM BbM EbM

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So there I moved from CM to EbM.

This particular example works particularly well because by going down from fifth to fifth, we follow the circle of fifth, adjacent scale to adjacent scale, each chord being the dominant chord of the following.

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So this is kind of the same technique than using dominant chords, but extended to several steps to reach a further tonality. This is like a series of authentic cadences.

In the same way, if we chose to make a sequence with ascending fifths, it would be like a series of plagal cadences, because each chord would then be the IVth degree of the next one.

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You can also make another kind of modulation, that is chromatic. That means by going up or down one semi tone. This is often used to add interest to a melody. This type of modulation is rather drastic as moving a up or down a semitone would be quite a long jump on the cycle of fifth, and this type of modulation don't always use a transition chord.

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And because this change of tonality can be so drastic, it is often definitive. 
If you move your whole tonality up or down a semi tone, this is not to go back to the original tonality right after.

Though doing a momentary modulation is something possible. But I think this should have its own video, so that's what we'll se in the next one.

The next video will be about borrowings and other ways you can use external notes to the tonality you're in.

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