A ladder of thirds (van der Merwe 1989, adapted from Curt Sachs) is similar to the circle of fifths, though ladders of thirds differ in being composed of thirds, major or minor, and may or may not circle back to its starting note and thus may or may not be an interval cycle.

Triadic chords may be considered as part of a ladder of thirds.

It is a modal frame found in Blues and British folk music . Though a pentatonic type the melodies come "into being through piling up thirds below and/or above a tonic or central note." (Middleton 1990, p.205)

Examples include The Beatles' "A Hard Day's Night" and are "commonplace in post-rock 'n' roll popular music - and also appear in earlier tunes" such as Buddy Holly's "Peggy Sue" and The Who's "My Generation", Ben Harney's "You've Been A Good Old Wagon" (1895) and Ben Bernie et al's "Sweet Georgia Brown" (1925).

Source

• Middleton, Richard (1990). Studying Popular Music. ISBN 0335152759.