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Summary: Completing the circle of fourths and keys with double flats

Double Flats

Having reached the key of Cb with all seven note flatted you could be forgiven for thinking that you have come to the end of the circle. But if that was the case it wouldn’t be called a circle as, by definition, circles don’t have ends!

So let’s continue applying the rules:

From Cb we go up four steps:

Cb Db Eb Fb

So the next key in the circle of fifths is Fb major.

Fb Gb Ab Bb Cb Db Eb Fb

The rules say we should now add a flat to the 4th note and we can see that this is necessary to maintain the major scale formula:

Fb [T] Gb [T] Ab [S] Bbb [T] Cb [T] Db [T] Eb [S] Fb

Bbb sounds the same as A but we can’t call that note A in a key where we already have an Ab.

Now you might complain that you have never seen a piece of music written in a key with double flats (they do exist, but are exceedingly rare). Later on we’ll discover exactly why this is.

However, even if you never play in these keys, it is important to understand the concept because, if you go on to study harmonizing (which is probably the most interesting and useful section of music theory for guitar players), you will need to be able to carry out theory work in all keys, including those with double flats.

So onwards:

The next key in the circle is:

Fb Gb Ab Bbb

The key of Bbb major.

It has 9 bs :

Bbb Cb Db Ebb Fb Gb Ab Bbb

Then up four to Ebb major with its 10 bs:

Ebb Fb Gb Abb Bbb Cb Db Ebb

And up another five steps to Abb major with 11 bs:

Abb Bbb Cb Dbb Ebb Fb Gb Abb

And finally we might imagine that the next key would be Dbb with 12bs:

Dbb Ebb Fb Gbb Abb Bbb Cb Dbb

But if we look closely we can see that:

Dbb =C, Ebb =D, Fb = E, Gbb =F, Abb =G, Bbb =A, Cb =B, and Dbb =C

So we are now truly back at the start of the circle in the key of C major which has no flats.


So that’s the circle of fourths, but, for every key with flats in the key signature there is one that sounds the same, but uses sharps instead of flats. You can read all about sharp keys in the circle of fifths.

If you have already sorted the circle of fifths out then take a look at the second part of the Key signatures page where we bring all this magical stuff together so that it (hopefully) makes sense!

Related pages
 Key Signatures
 Circle of Fourths
 Circle of Fifths
 Double Sharps
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 Nick Minnion