The latter lead to group 2, which includes the organ chorales (chorale preludes) of Buxtehude, Pachelbel, Bach, Brahms, et al., as well as the chorale choruses in cantatas and Passions.
Group 3 includes some motets
of the 13th and 14th centuries and many Masses
of the 15th century.
The cantus firmus appears most frequently in the tenor, usually in long notes that contrast with the more florid design of the other parts. In the 13th century, its rhythmic structure was determined by the system of the rhythmic modes, in the 14th by the principle of isorhythm. In the 15th century and later the cantus firmus often occurred in long notes of equal value.