Circle Theory
Copyright © 2008–2013 by Josef W. Wankerl, All rights reserved.

Circle Theory is a Circle Of Fifths (sometimes known as a Circle Of Fourths). The Circle Of Fifths is a tool for musicians to assist them in seeing the relationship between notes, provide key signatures for both major and minor scales, assists in transposing between keys, and it also has a helpful guide to figure out note intervals per musical mode. An iPad VGA adapter can be used to view the circle on an external screen or projector.

Installation [ $4.99 USD ]

There are far too many uses for a Circle Of Fifths to describe them all here. Many better resources exist for such purposes. (You might want to start looking at the Wikipedia Circle Of Fifths page.) This guide describes how to change various circle settings, not how to best use the circle.

There are a number of shortcuts for manipulating the circle:

The Rings
The largest outer ring always shows the current tonic note / key signature. The inner ring is configurable to show a number of different convenience metrics: the number of sharps or flats in a key signature, the notes in the major triad for the key signature, the relative minor for a major key signature, a musical mode indicator, and a transposition assistant.

The most basic Circle Of Fifths has no inner ring. The center of the ring shows the key signature on a musical staff. The clef may be changed at any time to be the treble, bass, alto, or tenor clef.

The first inner ring display simply shows the number of sharps and flats in a particular key signature. (The number can also be obtained by simply counting the number of sharps and flats on the musical staff for the selected key.)

The second inner ring display shows the notes contained in the triad for a particular major key signature. (The notes can also be determined by using the musical mode inner ring display, selecting the key, and finding the notes that occur on the I, III, and V position next to the inner ring.)

The third inner ring display shows the relative minor key signature corresponding to its major key signature on the outer ring. The relative minor is always three positions clockwise on the circle from its relative major.

The fourth and most versatile ring display shows the note intervals per musical mode. All of the other convenience inner circle displays can be determined using the musical mode inner circle. For each mode, the interval is described by roman numerals. Roman numeral I is always at the tonic position. In the example below, the key of C# is selected in the dorian mode. The triad for C# is found by finding the notes next to the I, III, and V roman numerals (in the case of C# dorian, i-III-v). When the triad starts on an uppercase roman numeral, the triad is a major chord. When the triad starts on a lowercase roman numeral (as in the case of C# dorian), the triad is a minor chord. When the triad starts on a note with the raised circle, the triad is said to be diminished. The notes in the scale for C# dorian are all found along the inner mode ring, so you can construct the entire scale by starting at the root I position and observing the note names in sequence (I, II, III...). In the case of C# dorian, the notes are C# - D# - E - IV - G# - A# - B - C# (or i - ii - III - IV - v - vi┬║ - VII - i).

The final ring display shows a transposition assistant. The inside ring is the starting note or key and the outside ring is the transposed note or key. The example below is set to transpose from the key of F to the key of C. The note sequence of F-G-D-E in the key of F correlates to the sequence C-D-A-B in the key of C. Chords can also be similarly transposed. All chord qualities stay the same, only the root changes. For example, F major becomes C major. B minor seventh (Bm7) becomes F# minor seventh (F#m7).

Modes Everywhere
The inner rings, by default and to promote simplicity, operate exclusively in the Ionian (Major) musical mode. The exception, of course, is the musical mode inner ring. Often times it is useful to be able to allow the selected musical mode to affect the inner rings. To allow using musical modes for all inner rings, turn the Modes Everywhere setting on (Allow Modes Everywhere). To only allow the Ionian (Major) musical mode for inner rings, turn the Modes Everywhere setting off (Modes Only For Inner Modes), meaning that musical modes are only allowed when the inner ring is showing musical modes.