Relative and parallel keys – free music theory course

Every major key has two particularly close minor "cousins". It is essential not to confuse them.

Relative keys: same signature

C major and A minor use the same notes and the same key signature: they are relative keys. The tonic of the relative minor lies a minor third below the major tonic (it is degree VI).

G major ↔ E minor (1♯)
F major ↔ D minor (1♭)
E♭ major ↔ C minor (3♭)

Conversely, the relative major of a minor key is a minor third above. Moving to the relative key is the gentlest modulation of all: no note changes, only the centre of gravity shifts.

Parallel keys: same tonic

C major and C minor start on the same note but don't share a signature (none / 3 flats): they are parallel keys (in French, tons homonymes). Switching between them changes the lighting abruptly, like a cloud passing in front of the sun.

Listen to Frère Jacques in major, then turned into minor. That is exactly what Gustav Mahler does in the third movement of his Symphony No. 1: the nursery round becomes a strange, ironic funeral march.

M:4/4
L:1/4
Q:1/4=90
K:C
C D E C | C D E C | E F G2 | E F G2 |]

M:4/4
L:1/4
Q:1/4=70
K:Cm
C D E C | C D E C | E F G2 | E F G2 |]

Quick way to find the relative: on the keyboard, go down three half steps from the major tonic (C → B → B♭ → A). Or count three letter names down (C, B, A) and check that it spans 3 half steps.

Common mistake: thinking C minor is the relative of C major. No: it is the parallel minor. Relative = same signature; parallel = same tonic.

Romantic composers love major/minor parallel switching: Schubert in particular often "tips" a melody from major to minor (or the reverse) for a poignant effect. This is sometimes called modal mixture or borrowing.