Theory & harmony
Relative minor
The relative minor of a major key is the minor key that shares its key signature, found three semitones below the major tonic, A minor is the relative minor of C major.
Two keys share a key signature because they use the same seven notes; what differs is which note behaves as home. C major and A minor both have no sharps or flats, but a piece in A minor gravitates to A and treats G sharp as a raised leading note added by hand.
For a player, the practical value is that a key signature alone never tells you the key. Two sharps could be D major or B minor, and the difference shows in the first and last notes, in the accidentals that keep appearing, and in the harmony. Looking at the final bass note is the quickest test.
The reverse relationship is the relative major, three semitones above a minor tonic. The pairing is why scale practice is normally organised in relative pairs rather than in two separate lists.
Related terms
Every term in this glossary is taught in context somewhere in Arco's curricula, on the staff, on the keyboard, and on your own fingerboard at the same time.