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
Octave standard 88-key piano keyboard, while the C an octave higher is C. The notation "8" or "8" is sometimes seen in sheet music, meaning "play this an octave higher than written" ("all' ottava": "at the octave" or "all' 8"). "8" or "8" stands for "ottava", the Italian word for octave (or "eighth"); the octave above may be specified as "ottava alta" or "ottava sopra"). Sometimes "8" is used to tell the musician to play a passage an octave "lower" (when placed under rather than over the staff), though the similar notation "8" ("ottava bassa" or "ottava sotto") is also used.