The Circle of Fifths is a musical scale circle made up of intervals of fifths. Specifically, starting from any note and moving up or down by a fifth, the next note is reached, and this process continues until returning to the starting note. For example, starting from C, moving up a fifth (to G), and then up another fifth (to D), and so on, until returning to C, produces the Circle of Fifths for the key of C major.
The Circle of Fifths is widely used, especially for analyzing and understanding chord progressions and modulations. On the Circle of Fifths, each note is separated from its adjacent notes by intervals of fifths, so the chords formed by adjacent notes often have similar sound effects and tonal relationships. For example, the G major chord (G, B, D) and the C major chord (C, E, G) formed by the interval of a fifth between C and G on the Circle of Fifths have similar sound effects and tonal relationships. Therefore, in music in the key of C major, these two chords are often used as substitute chords for each other.
Aside from analyzing chord progressions, the Circle of Fifths can also be utilized to anticipate the next chord progression or modulation. For instance, when working in the key of C major, one can start with the G major chord and proceed down a fifth to reach the D major chord (D, F#, A), then move on to the A major chord (A, C#, E), before finally returning to the E major chord (E, G#, B). These chords can then be employed to predict the upcoming chord progression or modulation.