4. Scales & modes

In our musical system an octave is divided in 12 equal intervals, so we have 12 notes per octave. And in the most used scales, including major and minor, there are 7 of those notes.
The name of these scales will depend on 2 things: the fundamental, the first note of the scale. And the way the notes are spaced throughout the octave.

Let's take the scale of C major as an example. It's easy, it's only the white keys of a piano keyboard.


C is the root key of the scale, the note that feels like "home". And "major" is defined by the sequence of intervals from the root key.

So in this scale of C major, the first interval is from C to D, that's 2 semi - tones,  so 1 tone.

The next interval between D and E is also 2 semi - tones,  so 1 tone.
Then 1 semi - tone between E and F.
1 tone between F and G,
1 tone between G and A 
And 1 tone between A and B.
And there is 1 last semi - tone to go back on C


So the "major" scale is defined by se sequence of intervals: 1 - 1 - 1/2 - 1 - 1 - 1 - 1/2.

And this is something we can transpose to any tonality to have any major scale.

So if I want the major scale of G for instance.
It goes G  -one tone - A - 1 tone - B - 1 semi tone - C - 1 tone - D - 1 tone - E - 1 tone - F# - 1 semi tone - back to G

Which is the scale we ended up with in the video on consonances and dissonances.



The C major scale works because we defined C as our home note. 
But every major scale have a relative minor scale. This is other scale, that will be minor, but will use exactly the same notes. So the only difference between a major scale and its relative minor is the fundamental note that we call "home", that feels like "home.

The relative minor scale of a major scale is the one that take its 6th note as fundamental.
So for the C major scale for example, the relative minor scale is A minor. 
Taking the exact same notes from the C major scales that makes : A - B - C - D - E - F - G
That's the A minor scale.

Once again this "minor" scale is defined by the sequence of intervals that builds it.
Let's have a look at it.
So A to B is 1 tone
B to C is 1 semi tone
C to D is 1 tone
D to E is 1 tone
E to F is 1 semi tone
F to G is 1 tone
And G to A is 1 tone

So the sequence that define a minor scale is:
1 - 1/2 - 1 - 1 - 1/2 - 1 - 1


We can also transpose that to any tonality, to have any minor scale.
As an example, let's make the minor scale of E.
It goes: E - 1 tone F# - 1 semi tone G - 1 tone A - 1 tone B - 1 semi tone C - 1 tone D - 1 tone back to E
That is the relative minor of G major. They use exactly the same notes.



In the same fashion, from a major scale, we can take any note as a fundamental, as our home note. And then we start building a whole bunch of new scales.

This is what we called modes.

Starting with the C major scale, the C major scale is actually called the Ionian mode, or mode of C.
The scale that use de same notes but starting from D is called the Dorian mode, or mode of D
The scale that use de same notes but starting from E is called the Phrygian mode, or mode of E
Then the mode of F is called the Lydian mode
The mode of G is called the Mixolydian mode
The mode of A is called the Aeolian mode - that's the minor scale.
And the mode of B is called the Locrian mode


As any scales, these modes are defined by the suite of intervals that build them, so they can be built from any root note.

For example if I want the Lydian scale of G, we'll start with a G, then we'll follow the sequence of the Lydian scale.
which is 1 - 1 - 1 - 1/2 - 1 - 1 - 1/2.
That makes the scale G - A - B - C# - D - E - F# - G
That's the Lydian G scale.