The Circle of Fifths 4

So what happens with the key of F# or Gb then? These key signatures are a special case because they are written with 6 sharps or flats, but there are only 5 sharps or flats available. There are some very good related reasons why this happens:

1. Firstly in written music each letter is used exactly once in a key signature—the thing that varies is whether a note is natural, sharp or flat.


2. So, in the F# key signature the leading tone (i.e. maj7) of F# is F, but we use E# instead of F to avoid having both F# and F natural notes present which would make the written notation more confusing than it needs to be.


3. Likewise in the key of Gb we avoid having to name the 3rd and 4th degrees as Bb and B by using Cb instead of B.

This is how they look on the staff, F# first:

And the Gb key signature: