In music theory, a chromatic fourth, or passus duriusculus, is a melody or melodic fragment spanning a perfect fourth with all or almost all chromatic intervals filled in (chromatic line). The quintessential example is in D minor with the tonic and dominant notes as boundaries:
The chromatic fourth was first used in the madrigals of the 16th century. The Latin term itself—"harsh" or "difficult" (duriusculus) "step" or "passage" (passus)—originates in Christoph Bernhard's 17th-century Tractatus compositionis augmentatus (1648–49), where it appears to refer to repeated melodic motion by semitone creating consecutive semitones. The term may also relate to the pianto associated with weeping. In the Baroque, Johann Sebastian Bach used it in his choral as well as his instrumental music, in the Well-Tempered Clavier, for example (the chromatic fourth is indicated by the red notes):
