Diatonic Theory - Understanding Keys



When dealing with a Major Scale, it's Modes, and it's Chords you end up creating a "Key". The "Key" is used to explain the tonalities of a Major Scale, the sequence of Intervals of a Major Scale, and the Harmonies within the Major Scale as it relates to the chords the harmonies create within the Major Scale...or the Key.

Most of the examples and concepts will be based in the Key of C Major...or derived from the C Major Scale.

But they could be moved/transposed or created from any Major Scale you wish. In other words...the most 
common, and simplest, piece of a Key are the Intervals of a Major scale.

The Major Scale is series or sequence of Intervals. The Major Scale's Intervals will NEVER change on you. You can get an in-depth understanding of Intervals from my Intervals Series.

The Interval structure, and Interval Names for a Major Scale are:

Root <whole-step> 2/9 <whole-step> M3 <half-step> 4/11 <whole-step> 5 <whole-step> 6/13 <whole-step> M7 
<half-step> Root.

Once you get back to the Root, the sequence has started over. So, a Major Scale only has seven notes in it. Then those notes start over again.

This is a sequence or cycle of Intervals that is constant, and never changes regardless of the Root note of 
the Major Scale. The note names change between different Major scales, but the Interval structure never 
does. The Interval structure is static.

The Intervals of a Major Scale are commonly written out from Root to Root in Whole-steps and Half-steps 
like this:


So, let's look at a couple of Major Scales, or Keys, and see this common Interval sequence in ALL of them.

The Key of C Major:

C w D w E h F w G w A w B h C

The Key of G Major:

G w A w B h C w D w E w F# h G

The Key of D Major:

D w E w F# h G w A w B w C# h D

The Key of F# Major:

F# w G# w A# h B w C# w D# w E# h F#

Hopefully you can see that ANY of the Major Scales, or Keys, ALL have the same WWHWWWH Interval sequence.

This is a basic but is a very powerful, and necessary, concept that is needed to fully understand the 
functions of music in general and especially Modes and the Major Scale, or Key, they relate to.

To reiterate, if you play any Note and then play the Interval sequence of W-W-H-W-W-W-H, you will have the Major Scale with the Name of your starting note:

Root is G + the W-W-H-W-W-W-H sequence from G = the G Major Scale
Root is F + the W-W-H-W-W-W-H sequence from F = the F Major Scale
Root is C + the W-W-H-W-W-W-H sequence from C = the C Major Scale

Now you know the Interval sequence of a Major Scale/Key and how to create the scale/Key from a Root using the sequence.