The circle of fifths diagram reveals several important musical relationships and is one of the most important tools available to a musician. The circle of fifths diagram shows the relationship between major and natural minor keys as well as the most frequently used intervals for chordal harmonic movement.
The letters on the black ring refer to major key names and chord roots. The letters on the inside ring refer to minor keys and chord roots. The rings are arranged so that the major keys are adjacent to their relative minor counterparts. For example, A minor (in the inner ring) is the relative minor of C major (on the outer ring).
At the bottom of the circle of fifths diagram are some key names arcing around the inner and outer ring. These are enharmonic keys sharing the identical tone. For instance, the key of Cb has seven flats while the key of B has five sharps. Yet, since they refer to the same note, they are tonally equivalent.
When we think of the letters on the circle of fifths as representing chord roots, we see notes separated by intervals that create strong tonal movement. Moving clockwise on the wheel, we go from C to G to D, etc. This movement can be interpreted in two ways. First, if we are going up the scale, the interval from C to G is a fifth. Second, if we are going down the scale, the interval from C to G is a fourth.
On the other hand, if we move counter-clockwise around the circle of fifths from C to F to Bb, this movement can be interpreted in two ways. First, if we are going up the scale, the interval from C to F is a fourth. Second, if we are going down the scale, the interval from C to F is a fifth.
In the circle of fifths diagram you might have noticed that the relative minor of F is D. In the chord substitution section of the Harmonizer, we can see that the chord of Dm can substitute for F major. When we make the change, our I, IV, V, I progression turns into a I, IIm, V, I progression: C, Dm, G and C.
You might now notice that on the outer ring of the circle of fifths diagram we can read (going counterclockwise) the same root notes of the IIm, V progression finishing with the I chord (G, D, C). In fact, it goes beyond that. You can see that the very popular IIIm, VIm, IIm, V7, I progression is derived from the circle of fifths as well. In C major that progression would be Em, Am, Dm, Gdom7, C.
The IIm-V7 (often called two-five) combination of chords is called a turnaround and is frequently used in jazz. Any two consecutive roots on the wheel moving counter-clockwise produce a IIm-V7 turnaround combination.
The combination is often played the end of a musical phrase because it Òturns aroundÓ the chord progression and starts it over again. A turnaround usually leads to the tonic chord. In the key of C major, the turnaround would be Dm (IIm), Gdom7 (V7), C (I). You will notice that if we begin on the D on the outer ring of the circle and move counter-clockwise, we encounter the G and the C in the same order as played to create a turnaround.
Finding the Tonal Center
Another use for the circle of fifths is analyzing tonal centers of a piece of music. Often a piece of music will change keys. (You canÕt always tell the tonal center just by looking at the key signature.) However, since the presence of a dominant chord often determines the tonal center, the wheel can suggest a possible center. To find the center, identify the root of the dominant chord on the outer ring and move along counter-clockwise one note. This note will probably be the center. For instance, if a Ddom7 appears in a piece of music, find the D, then move counter-clockwise one note. The result is G, the tonal center.