Musical Keys and the Circle of Fifths
There’s a method to the madness of key signatures that makes your piano playing easier. The Circle of Fifths is an order that starts with no sharps and flats and cycles the ring of keys to all twelve keys. As you travel around the circle, you find each of the 12 keys in the tonal system. The numbers inside the circle tell you the number of sharps or flats in each key signature:
Note the following important points about the Circle of Fifths:
Each key is a fifth up from the previous key, circling clockwise.
The key of C, at the top, has no sharps or flats.
The keys on the right half of the Circle are all sharp keys, gaining one sharp at each position traveling clockwise from the top.
The keys on the left half of the Circle are all flat keys, gaining one flat at each position traveling counterclockwise from the top.
The three keys at the bottom of the circle can be either sharp or flat keys; the composer gets to decide.
The Circle shows the relationship of the keys to each other. Neighboring keys have a lot in common, like seven of eight scale tones. Very often a song travels smoothly to a neighboring key during its musical journey. The keys farthest away from each other have little in common, and a musical journey from one side of the Circle directly to the opposite side sounds quite abrupt.
The order of sharps and flats as they’re written on the grand staff follows the Circle of Fifths, adding a sharp or flat in the same order as the Circle.
Key signatures with sharps
Suppose you want to play a song on the piano that has two sharps in the key signature. If you look at the Circle of Fifths, you can quickly see that the key with two sharps is in the key of D. Eventually you want to be able to know what key a song is in without glancing at the Circle. Here’s how:
To read a key signature that contains sharps:
Locate the last sharp (the one farthest to the right) on either the treble or bass clef.
Move up one half-step from the sharp to find the name of the key.
For example, if you have two sharps, F-sharp and C-sharp, the last one is C-sharp. Up a half-step from C-sharp is D. The song is in the key of D.
Key signatures with flats
To read a key signature that contains flats:
Locate the next-to-the-last flat (the one that’s second from the right) in the key signature.
The name of that flat is the name of the key.
For example, if you have three flats in a key signature — B-flat, E-flat, and A-flat — the next to the last one is E-flat, and the song is in the key of E-flat.