Music Theory Music Theory

Published on June 2nd, 2014 | by Sam


Key Signatures and the Circle of Fourths

Each scale (aka key) has its own unique set of sharps and flats.  This is called its “key signature.” The only way to figure these out from scratch is to build each scale individually from the intervals listed above.  If you ALREADY know the key signatures though it is easy to apply these to each note in order to get a scale.

If we wrote out all of the major scales we would end up with:

All Major scales

Notice that some scales have 1 sharp, then 2, then 3.  Did you see that the key with 1 sharp (G) has an F#, then the key that has 2 sharps (D) has both the F# and a C#.  The same pattern holds with the flats.  So each key will add a sharp, or add a flat.  Now, put the keys in order of the number of sharps.  Start with C in the middle because it doesn’t have any sharps or flats.

Major scales Keys 1

Towards the left we will add flats.  The first key with flats will be F, so it should go to the left of C.  Then keep going until you have all of the flat keys.

major scales key 2

Now let’s add sharp keys toward the right.

Major Scales all

The order that we have come up with is called the Circle of Fifths.  Right now it’s the Straight Line of Fifths (not a real term FYI!), but if it’s presented in a circle, we get the Circle of Fifths.  As you move around the circle clockwise, the keys go up by a perfect fifth (7 half steps).  Moving around the circle counter clockwise the keys move by fourth (5 half steps).  Most common chord progressions move this way – by fourth.  So it is very important to have a good understanding of the cycle in both directions.

Cycle of fifth circle of fifths

The order of sharps and flats also moves around the cycle.  Let’s look at flats first.  The key with 1 flat (F) has a Bb.  The next key (Bb) has Bb and Eb.  The key with 3 (Eb) has Bb, Eb, and Ab.  This is also the same order that they appear counter-clockwise on the cycle!  The sharps are added the same way, just clockwise through the circle.

So now, if you know the Cycle of Fifths you can easily figure out the key signatures of each major scale.   You can also figure out the spellings of all the scales using the key signatures.  All you have to do is apply the key signature that you have figured out to the notes in the key.

You have are trying to figure out the spelling of the key of Eb, you first find that Eb has 3 flats (Bb, Eb, and Ab).  Start by writing out E to E without any sharps or flats.


Then put your flats in:

Eb F G Ab Bb C D Eb – that’s it!  That’s not so bad right?

Part 1    Part 3    Part 4

 (Photo Credit: Surat Lozowick)

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