Arpeggio
An arpeggio is a chord whose notes are played one after another instead of all at once, usually rising from the lowest note to the highest or falling back down.
What does an arpeggio look like?
Take the C major chord, C–E–G, and play its notes in turn: C–E–G–C, then back down. That is a C major arpeggio. A minor gives A–C–E–A; G7 gives G–B–D–F.
The name comes from the Italian arpeggiare, “to play like a harp”, because a harp sounds a chord by plucking its strings in turn.
Two pieces built almost entirely on arpeggios: the Prelude in C major that opens Book 1 of Bach’s Well-Tempered Clavier, and the first movement of Beethoven’s “Moonlight” Sonata, where the right hand rolls through each chord in steady groups of three. On guitar, fingerpicking a chord shape one string at a time is arpeggiating it.
How do you recognise one?
The line leaps instead of stepping, and every note it lands on belongs to the same chord. If you could stack the notes of a passage into one chord without a clash, you are probably hearing an arpeggio. With the sustain pedal down or the strings ringing, you hear the chord build up note by note.
What is it confused with?
A scale. A scale steps through every note of a key in order: C–D–E–F–G. An arpeggio skips straight to the chord’s notes: C–E–G. Practising both is common because they train different things, the key and the chord.
A broken chord is the wider term for any chord played note by note, in any pattern. The Alberti bass, C–G–E–G repeated, is a broken chord that does not run straight up or down. Many people use the two words interchangeably.
Try it: Building chords has you find each triad on your instrument; play its notes one at a time and you have its arpeggio. The harmonic field lesson shows the seven chords of a key you can arpeggiate in turn.