Key signature: The circle of fifths

The circle of fifths

The circle of fifths is an illustration that has been used in music theory pedagogy for hundreds of years. It conveniently summarizes the key signature needed for any key with up to seven flats or sharps. As you might have noticed, the circle of fifths is so named because each note in the circle is a perfect fifth away from its neighboring notes.

The most common usage for the circle of fifths is to help determine key signatures. Starting at the top of the circle with the key of C and moving clockwise tells you how many sharps there are in the major key of that note. For example, moving on space to the right on the circle brings you to G, so you know that G major has one sharp. Figuring out which notes are sharped is also made easy by the circle of fifths, by moving clockwise starting at F.

Similarly, reading the circle in the counterclockwise direction will help with flat keys (F has one flat, Eb has three flats, etc.). To figure out which notes are flatted, start from B and move counterclockwise.

Beyond simply making key signatures easier to memorize, the circle of fifths has many useful applications across music theory. In Western harmony, the circle of fifths is useful for identifying common chord progressions. For example, dominant 7th chords generate tension because of the tritone interval between the 3 and the flat-7 of the chord, and this tension naturally wants to resolve to the tonic chord a fifth down, which is why the V chord of any key is usually written as a V7 in Western functional harmony. Additionally, the IV-V-I chord progression is very common in Western music, and these three notes are all located very close to each other on the circle of fifths.

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