The Single Line
During the sixteenth century a number of treatises dealing with counterpoint were written. Several authors, among them Gioseffo Zarlino and Thomas Morley, used an approach in which the simplest steps were presented first, then modifications and difficulties were gradually introduced one by one. Characteristic of this approach was the presentation to the student of a given unchangeable melody, called the cantus firmus (“fixed song”), against which the student wrote counterpoints. At first only one note was placed against each note of the cantus firmus-note against note, or in Latin, punctus contra punctum. After this step was mastered, two notes were placed against one, and so forth in various combinations called species.