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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, major and minor. That's a dominant chord, it works also in minor tonalities because that emphasis the tension From V to I. And we can emphasis this tension by making this Vth degree chord a dominant 7th chord, with a major third and a minor 7th.

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

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 neighbour tones. It's because between CM and Cm there are more notes that are différents, so the change would be a bit more drastic.

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 my chord progression in Dm: Dm BM Gm.
I can make the transition smoother by adding a A7 chord just before the Dm, A being the fifth of D.
Or in thé same way I could use a C7 if i want to go to FM or a D7 if I want to go to GM

The authentic cadence and the tension a dominant chord creates is really handy to announce where you are going with you 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 instance

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.

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 do our modulations.
Step 1: create a pattern, or a chord, I'll take CM
Step 2: chose a direction and an interval. The most used in the descending fifth, so I'll take this one as an example. But ascending G 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
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, neighbour tone to neigh tone, each chord being the dominant chord of the following chord.
So this is kind of the same technique than using dominant chords, but extended to several steps to reech a further tonality. This is like a series of authentic cadences.

In the same way, a sequence of ascending fifth would be like a series of plagal cadences, each chord being the IVth degree of the next one.

You can also make another kind of modulation, that is chromatic. That means by going up or down a semi tone. This is often used to add interest to a melody. This type of modulation is rather drastic as moving a tonality 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. 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, and that's what we'll talk in the next video that will be about borrowings and other ways you can use external notes to the tonality you're in. If you liked this video consider giving it a like and subscribe and hit the bell button if you don't want to miss the next videos of this series. In the meantime, thanks for watching, and I'll se you next time!

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