The Circle of Fifths

As you probably know, "keys," in music, involve different root notes, and different notes on each scale degree as a result of that. To determine the notes in a key, we refer to the circle of fifths, which tells us the number of sharps or flats in a particular key signature.

The order of sharps is this:

F-C-G-D-A-E-B

and the order of flats is simply the reverse:

B-E-A-D-G-C-F

But what the heck does that mean!? Well, it means that if the key has, for example, only one sharp in its diatonic form, that sharp will be F. If it has TWO sharps, it will be F and C. Three: F, C, and G. Etc etc.

For flats, we do the same thing. Now to determine how many sharps or flats are in a given key, we use the circle of fifths:



Now we can see which key signature has a particular number of sharps or flats. Starting from Cmajor/Aminor, which have zero sharps and flats, we travel up a fifth, and find that Gmajor/Eminor have ONE sharp, hence the name "circle of fifths."

A quick example of the importance of knowing the sharps or flats of a key: C minor has three flats, and, thanks to the order of flats, we now know they are B, E, and A. Because we don't mix sharps and flats in a key signature, AND we know all the flats of this key, we can infer that all the other notes are naturals. Therefore, the notes in Cminor MUST be C, D, Eb, F, G, Ab, Bb, C.