Before there were named modes and modal harmony, there was music. The concept of modes developed to provide a way to systematize, classify and describe music that already existed, and to regularize the composition of new music. There are seven modes. Each of them uses the eight notes in a diatonic octave, but each has a different tonic, or starting note. Two historical traditions came together to create the modes that are recognized and used today.
The ancient Greeks were among the first to think about the possible arrangements of the pitches in an octave, which they called "tonos." They named these arrangements after people of various regions in the ancient Mediterranean world: Ionian, Dorian, Aeolian, Locrian, Lydian and Phrygian. Greek philosophers Plato and Aristotle recognized that music in different modes varied in feeling, promoting emotions such as sadness, even temper and enthusiasm.
The sixth-century Roman philosopher Boethius wrote about ways of tuning a stringed instrument called a cithara and continued thinking about Greek "tonos," for which he used the Latin word "modus." From this comes the English word "mode."
Ambrose, Bishop of Milan, Italy in the late fourth century, also identified four modes, based on the notes D, E, F and G. The number of modes was increased to eight in the late sixth century. These eight modes were based on the white keys of the piano; there were no sharps and flats. Useful in the composition of Gregorian chant, which had only one melodic line, they became problematic when polyphony -- more than one melody line -- was introduced during the Middle Ages.
By the time of the Renaissance, in the 15th and 16th centuries, the old Greek names were again associated with modes based on the seven diatonic pitches: The Ionian mode beginning on middle C, the Dorian mode on D, the Phrygian mode on E, the Lydian mode on F, the Mixolydian mode on G, the Aeolian mode on A and the Locrian mode on B. With the introduction of sharps and flats, each mode could be started on the pitch of C and have a different key signature. The Lydian, Ionian and Mixolydian modes are called major modes, because they each have a major third from the first degree of the scale to the third. The other modes are called minor, because they have a minor third from the first scale degree to the third.
During the Baroque period, between 1600 and 1750, use of modal harmony in composition was restricted to the Ionian (major) and Aeolian (minor) modes. The minor mode, however, was often modified by the use of a raised seventh degree leading tone, or accidental, to produce a more pleasing minor sound. By this period, modes had become the rules, rather than the descriptors, of the harmonies to which they related. Composers like Bach were strict followers of the rules of modal harmony.
Since the Baroque, use of the seven modes and their associated harmonies has again proliferated. International folk music is typified by mode: Irish traditional music uses the Ionian, Dorian, Aeolian and Mixolydian modes; flamenco, Central European and some Arab music use the Phrygian mode; Latin and Laotian music use the Dorian mode; jazz and much popular music use the Mixolydian mode; soundtrack and video game music often use the Lydian mode. Nineteenth and 20th-century classical composers also routinely used a variety of modal harmonies. Combining diatonic tones by means of modal harmony helps composers and musicians add color and mood to their music -- just as Plato and Aristotle said it would.