Lesson 15: Major and Minor Keys

When a piece of music is "in the key of G major", it means the notes of the G major scale are its home territory: melodies are built from those notes, chords are built on them, and the music keeps returning to G as its resting point. The key of a piece is its tonal centre — the note and scale that everything else relates to. Understanding keys is understanding how music is organised.

Every key has a key signature: the sharps or flats written at the start of each staff, just after the clef, that apply to every note of that name throughout the piece. C major and A minor have no sharps or flats. G major has one sharp (F sharp); D major has two (F sharp, C sharp); F major has one flat (B flat); B flat major has two (B flat, E flat). The key signature saves the composer from writing a sharp or flat sign before every single affected note. A musician who reads the key signature at a glance knows immediately which notes to raise or lower.

Relative and Parallel Keys

Every major key has a relative minor that shares its key signature: the relative minor starts on the sixth note of the major scale. C major's relative minor is A minor (no sharps or flats); G major's is E minor (one sharp); F major's is D minor (one flat). Relative keys share the same notes but have different home notes, so they sound quite different. There is also a parallel relationship: C major and C minor share the same tonic note, C, but C minor has three flats in its key signature (B flat, E flat, A flat). Parallel keys sound like two moods of the same home; relative keys sound like two different homes that happen to share the same notes.

Changing Key: Modulation

Pieces do not always stay in one key. Modulation is the move from one key to another within a piece, and it is one of the most powerful tools a composer has. A song might start in C major, move to G major for its middle section — a closely related key, only one sharp different — and return to C for the end. The move creates a feeling of journey and fresh energy. Composers usually modulate to a related key (one nearby on the circle of fifths, which the next lesson explains) so the move feels smooth, and they often use a shared chord — a chord that belongs to both keys — as a bridge between them.

Finding Keys Quickly

There are two quick tricks for working with keys. First, to find the relative minor of any major key, go down three semitones (a minor third) from the tonic: from C down three semitones is A, so A minor is the relative minor of C major; from G down three is E, so E minor is the relative minor of G major. To find the relative major of a minor key, go up three semitones instead. Second, the key signature tells you the key at a glance if you know the last sharp or flat. The last sharp in a key signature is the leading note of the major key — one semitone below the tonic — so a signature ending in F sharp is G major. The last flat in a key signature is the subdominant, one step below the tonic in the alphabet of flats: a signature ending in E flat is B flat major, because B flat is the next flat in the order after E flat. These tricks mean you never have to memorise a table of twenty-four keys: the pattern of sharps and flats, and the circle of fifths from the next lesson, will generate any key you need.