A polychord is a chord that consists of two or more triads stacked on top of each other. The triads can be major, minor, augmented, or diminished.

The most common type of polychord is a major-minor seventh chord. This chord is created by stacking a major triad on top of a minor seventh chord.

Polychords can be used to create tension and release, to add color and richness to a chord progression, and to create a sense of movement. They are a powerful tool that can be used to create a variety of musical effects.

Polychords are notated by writing the two chords together, with a slash between them. For example, a C major triad over a G minor seventh chord would be notated as C/Gm.

The opening chord of the Beatles' song "A Day in the Life" is a C major triad over a G minor seventh chord. This polychord creates a sense of tension and release that is characteristic of the song.

The opening chord of the Miles Davis song "So What" is a D minor triad over a G minor seventh chord. This polychord creates a sense of ambiguity and uncertainty that is characteristic of the song.

The opening chord of the Bach's "Toccata and Fugue in D Minor" is a D minor triad over a G minor seventh chord. This polychord creates a sense of power and majesty that is characteristic of the piece.

Polychords can be challenging to use because they can be difficult to voice, difficult to resolve, and difficult to use in a melodic context. However, when used effectively, polychords can create a variety of musical effects that can be very powerful.

Polychords can be used to create tension and release, to add color and richness to a chord progression, and to create a sense of movement. They are a powerful tool that can be used to create a variety of musical effects.

The best way to learn more about polychords is to read books and articles about them, listen to music that uses them, and experiment with them in your own music.