Circle of Fifths

The Circle of Fifths is a chart representing the twelve most common key signatures, each separated by an interval of a perfect fifth going clockwise around the circle. It can be used to display both Major and minor key signatures.

The Circle
This is a homemade diagram of the circle of fifths. Going clockwise around the circle results in key signatures a perfect fifth apart; going counterclockwise results in key signatures a perfect fourth apart. (The keys shown are the actual keys that result from the intervals--meaning, the supposed G♯ that comes after C♯ is actually A♭ due to enharmonics.) Each successive key going one direction gains a sharp or flat, depending on the direction; C/a has no sharps or flats. (This means that G/e has one sharp, then D/b has two, A/f♯ has three, etc.; and F/d has one flat, B♭/g has two, etc.) This circle shows both Major keys and their relative minor keys, represented by uppercase and lowercase letters, respectively. The dotted line between f and b♭ and between c♯ and g♯ mean that the minor part of the circle continues along those lines (meaning, it tells you f goes on to b♭ instead of to a♯).

The circle is primarily used as a reference device for composers and musicians. There is a different kind of circle of fifths used by composers that uses chords instead of keys, though it goes in fifths when going backwards through it, and instead goes in fourths going forwards. (This may be because a perfect fourth is made of five semitones.) Going forwards through it--in a progression of I-IV-vii°-iii-vi-ii-V-I--is a valid progression when abiding by normative rules. However, as Pachabel's Canon proved, going backwards through the circle can result in a satisfying progression, as well.