Relative Major and Relative Minor

Two scales can use the same seven notes and still sound totally different, because what makes a key sound the way it does isn't just which notes are available, it's which note feels like home. That home note, the tonic, is where melodies land and where the ear expects rest. C major and A minor use the identical seven white keys, but a tune built to rest on C feels bright and settled in a major way, while a tune built to rest on A feels darker and unsettled, even though every single pitch involved is shared between them.

The relationship is fixed and easy to find: the relative minor's tonic always sits three half steps below the relative major's tonic. Start on the major tonic, count down three half steps, and you land on the relative minor's tonic. Those two keys then share one key signature, because the notes themselves never changed, only the starting point and the pattern of whole and half steps built from that new starting point. Go the other direction, up three half steps from a minor tonic, and you find its relative major.

This matters because every key signature you memorize does double duty: one signature names a major key and its relative minor at once, so learning key signatures really means learning fifteen pairs, not thirty separate keys. It also sets up natural, harmonic, and melodic minor, since all three forms of a given minor key still share that same relative major and that same signature, only the minor scale itself gets altered note by note.