Octave species various available intervals could be combined in any order, even restricting species to just the diatonic genus would result in twelve ways of dividing the octave (and his 17th-century editor, Marcus Meibom, pointed out that the actual number is 21), but "only seven species or forms are melodic and symphonic" . Those octave species that cannot be mapped onto the system are therefore rejected . In chant theory beginning in the 9th century, the "New Exposition" of the composite treatise called "Alia musica" developed an eightfold modal system from the seven diatonic octave species of ancient Greek theory, transmitted to
Steps and skips step will always be a movement of 1 or 2 semitones, and a skip a movement of 3 or more semitones. In other scales an augmented second—an incomposite step equivalent to 3 semitones—and/or a diminished third—a skip of 2 semitones—may be possible. Melody may be characterized by its degree and type of conjunct and disjunct motion. For example, Medieval plainchant melodies are generally characterized by conjunct motion with occasional thirds, fourths, and generally ascending fifths while larger intervals are quite rare though octave leaps may occur between two separate phrases. Renaissance melodies are generally characterized by conjunct motion, with only