Parallel tonic chords on C.
In music, parallel keys are the major and minor scales that have the same tonic. A major and minor scale sharing the same tonic are said to be in a parallel relationship. The parallel minor or tonic minor of a particular major key is the minor key based on the same tonic; similarly the parallel major has the same tonic as the minor key, as opposed to relative minor (or major, where appropriate) which shares the same key signature. For example, G major and G minor have different modes but both have the same tonic, G; so we say that G minor is the parallel minor of G major.
In the early nineteenth century, composers began to experiment with freely borrowing chords from the parallel key.
To the Western ear, the switch from a major key to its parallel minor sounds like a fairly simplistic "saddening" of the mood (while the opposite sounds like a "brightening"). This change is quite distinct from a switch to the relative minor.
Calculating the key signature of the parallel major or minor key
Flats always appear in the order B-E-A-D-G-C-F. Sharps always appear in the opposite order F-C-G-D-A-E-B.
For example, if there are three flats in the key signature, those flats would be B, E, and A. If there are two sharps in the key signature, they would be F and C.
- To find the parallel minor of a major key, add three flats to the key signature (or remove three sharps).
- For example, the key of F major has 1 flat (B♭). Adding 3 flats would yield 4 flats, meaning F minor consists of B♭, E♭, A♭, and D♭.
- B major has 5 sharps (F♯, C♯, G♯, D♯, A♯). To find B minor's key signature, add 3 flats. Since flats cancel out sharps, one is left with only 2 sharps (F♯ and C♯).
- To find the parallel major of a minor key, add three sharps (or remove three flats).
- E minor to E major: E minor has 1 sharp (F♯). Add 3 to get 4 sharps (F♯, C♯, G♯, D♯).
- F minor to F major: F minor has 4 flats (B♭, E♭, A♭, D♭). Add 3 sharps to get F major's key signature. Since sharps cancel out flats, one is left with only 1 flat (B♭).
In practice, sometimes the enharmonic parallel major or minor is used instead. For example, Chopin's Fantaisie-Impromptu switches from C♯ minor to its parallel major. This could be notated as C♯ major with 7 sharps, but is written as D♭ major, with 5 flats, instead.
An example of switching from minor to major key is at the 20:06 marker of Keith Jarrett's Koln Part 1. The first portion of the song is exclusively a vamp in A minor and then an abrupt switch to A major for the remaining 5:52.