08. Natural, harmonic and melodic minor scales

Last time, we talked a bit about cadences and we said that we could replace the V chord by a dominant 7th chord to add a little bit of tension.
And another reason why this Vth degree creates a tension with the Ist degree, is because of how the chord itself is built.

In the scale of C major, the Vth degree chord, which is G, is built with the root note G, the major third B and the perfect fifth D.
This note B is very close, just a semi tone away from the tonic C of our scale. And this fundamental have such as strong role in this scale, that this B wants to climb up this little semi tone to go to the tonic. That's why it's called the leading tone. Because it creates this friction that generally leads to the tonic.

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If we look at a minor scale, like A minor, the Vth degree is supposed to be a minor chord. Right?
But when you use this chord to make a cadence, (so V - I in A minor would be Em to Am).
When you make a cadence, you can make it major to have this leading tone a half step below the tonic and add friction to you chord progression. So the E chord would lead more easily to this A chord, using this leading tone.

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In fact any dominant chord (chord of Vth degree) that is preparing a cadence can be made major, in any tonality.

So in A minor it allows you to use the note G# that is normally not in the scale (to build our E major chord on the degree V).

MINOR MELODIC AND MINOR HARMONIC 

The minor scale as we've seen it so far, is actually only one kind of minor scale, that we call the natural minor scale.

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This possibility to play a major chord on a fifth degree of a minor scale adds an altered note, and that actually creates an alternative minor scale that is called harmonic minor scale.

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Harmony is the combination of several tones played simultaneously, thus chords.
This harmonic minor scale allows us to have a major chord of the Vth degree, and therefore create better authentic cadences in a minor tonality.

In the same way we did the video about scales, we can transpose this scale to any tonality, as long as we sequence of intervals that build it.

So the sequence of intervals that build it is:
1 - 1/2 - 1 - 1 - 1/2 - 1,5 - 1/2

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This scale is great harmonically, but melodically this 1,5 tone between the 6th and the 7th note is quite a big gap. As to make a great melody, smaller intervals are often preferred.

This bothered composers enough for them to create a third minor scale, by raising this 6th note by a semi tone. The gap between the 6th and the 7th note being now reduced to only 1 tone. This is what we call the melodic minor scale. And the sequence of intervals that defines it is 1 - 1/2 - 1 - 1 - 1 - 1 - 1/2

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In fact this melodic minor scale is just like the major scale, except that the 3rd is minor.

The handy thing is that when you are using a minor tonality, you can rather freely use the natural, harmonic and melodic minor scales at the same time, depending on the context.

Mainly using the natural scale, then using the harmonic scale for cadences and the melodic scale for certain melodic movements.

Which can make minor tonalities very rich in possibilities.

DOMINANT 7TH

So when we play a chord of Vth degree, its third will create a tension. And we can emphasis this tension by making the chord a 7th chord.
For a G chord it will become G B D F.
The interval between the B and the F here is a diminished fifth, and this is very dissonant.

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This dissonance adds to the friction created by the leading note, making it even more powerful. 
This configuration - a major third, with a perfect fifth and a minor 7th - is called dominant 7th chord because that's the chord often used on the dominant to resolve on the tonic. (Like a G7 resolving to a C, the G7 being the V and the C being the I)

Using the same logic, you can also use this dominant 7th chord on any Vth degree of any scale if it's preparing a cadence.

So I can resolve this G7 chord by going to C minor instead of C major. 
Or I can use a E7 chord to resolve on either a AM or a Am.
Or use a D7 to go to either a GM or a Gm

 These dominant chords and dominant 7th chords are very useful in many situations, but before we get there, in the next video I'll explain what's the cycle of fifths, which is one of the most powerful tool a composer can have. this is the figure I've been using, and I'll explain all the info you can get from it. It's a very useful tool.

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