Chords and keys

How notes group into harmony, and how a piece establishes its home note.

What it is

A chord is three or more notes sounded together; a triad is the basic three-note chord. A key is the home tonality, defined by its key signature and its tonic. Cadences are the standard chord pairs that end phrases — perfect, plagal, imperfect and interrupted.

Where it applies

GCSE and A Level music.

How it works

Roman numerals label chords by their position in the key: I, IV and V are the primary chords and carry most popular music.

Modulation is moving to a new key, most commonly to the dominant or the relative minor.

How to use it in your work

Learn the four cadences by sound as well as by name — listening questions ask you to identify them.

In composition, use functional harmony rather than random chords, and cadence properly at the end of phrases. Examiners notice.

Where to get help

Your teacher and your board's assessment criteria — these subjects are marked against four or five stated objectives, and reading them is the single most useful hour you can spend.