Related introduction:
These modes have one thing in common: their scales are composed of seven notes, all of which are natural and have no inflections, just as people only play on the white keys of the piano, so people also call these modes "natural mode system".
First of all, there are four tones that can be used as tonic: re, mi, fa and sol. Based on them, four positive styles can be formed: doria, Phrygia, Lydia and Mixed Lydia. These names came from ancient Greece, but they were rarely used in the Middle Ages.
Extended data
Aristotle (Aristotle) and cleo (Cleonides) pointed out that the four-tone scale is the foundation of the whole music system, which is arranged from top to bottom. The two tones at both ends form a fixed quartic interval, and the two tones in the middle can be changed, thus forming three different quartic scales: natural tone, tone sandhi and quarter tone.
Two quartets can be connected into an octave through "cohesion" or "separation", four quartets can be connected into a "big complete system" and three quartets can be connected into a "small complete system".