Toonsoort

Toonsoort is a term in music theory that denotes the key or tonal center of a piece. It specifies the scale and harmonic system used for melodies and chords and is usually identified by a key signature and, when stated, by the name of the key (for example, C major or A minor).

Most Western tonal music uses two primary modalities: majeur (major) and mineur (minor). The major key is typically described as bright, while the minor key has a darker character. Each major key has a corresponding relative minor key that shares the same set of pitches, located a minor third below (for example, C major and A minor). Parallel keys share the same tonic but a different mode (C major vs C minor).

Keys are related through the circle of fifths, which shows smooth transitions by adding sharps or flats to gradually move from one key to another. In composition, modulation is the process of changing to a new toonsoort within a piece; in performance, transposition shifts all notes to another toonsoort to suit an instrument or voice range.

Notation uses key signatures: C major and A minor have no sharps or flats; G major and E minor have one sharp; F major and D minor have one flat. The choice of toonsoort influences chord functions, scale degrees, and melodic tendencies, but many works use several toonsoorten through modulation or modal mixture.