Partbooks
The manuscript or printed books of the 15th and 16th centuries, each containing
the music for an individual voice of a polyphonic
composition. The usual number of partbooks in a set is four:
Cantus (Discantus, Superius); Altus; Tenor;
Bassus (Basis). Publication in partbooks clearly indicates
that the music thus written or published is ensemble music, either vocal,
or instrumental.