Introduction In many music traditions, including Western music, the list of all the notes that are expected or allowed in a particular piece of music is a scale. A long tradition of using scales in particular ways has trained listeners to expect certain things from a piece of music. If you hear a song in C major, for example, not only will your ear/brain expect to hear the notes from the C major scale, it will expect to hear them grouped into certain chords, and it will expect the chords to follow each other in certain patterns and to end in a certain way. The expectations for music in a minor key are a little different than for music in a major key. But it is important to notice that you can move that song in C major to E major, G flat major, or any other major key. It will sound basically the same, except that it will sound higher or lower. (For more on this subject, see Major Scales, Minor Scales, Scales that aren't Major or Minor, and Transposition.) This sameness is not true for musical traditions that use modes instead of scales. In these traditions, the mode, like a scale, lists the notes that are used in a piece of music. But each mode comes with a different set of expectations in how those notes will be used and arranged.

Comparison of Scale and Mode Compare the differences and similarities between the two major scales, and the differences and similarities between the two medieval church modes. The figure above shows two scales and two modes. The two major scales use different notes, but the relationship of the notes to each other is very similar. For example, the pattern of half steps and whole steps between them is the same, the interval (distance) between the tonic and the dominant is the same. Compare this to the two church modes. The pattern of whole steps and half steps within the octave is different; this would have a major effect on a chant, which would generally stay within the one octave range. Also, the interval (distance) between the finalis and the dominant is different, and they are in different places within the range of the mode. The result is that music in one mode would sound quite different than music in the other mode. You can't simply transpose music from one mode to another as you do with scales and keys; modes are too different.

The Classical Greek Modes We can only guess what music from ancient Greek and Roman times really sounded like. They didn't leave any recordings, of course, nor did they write down their music. But they did write about music, so we know that they used modes based on tetrachords. A tetrachord is a mini-scale of four notes, in descending pitch order, that are contained within a perfect fourth (five half steps) instead of an octave (twelve half steps).

Tetrachords Here are three possible Greek tetrachords, as nearly as they can be written in modern notation. The outer notes are a perfect fourth apart; we can be pretty certain of that, since the perfect fourth is a natural interval playable, for example, on many ancient wind instruments (See The Harmonic Series and Interval). The actual tuning of the inner notes can only be guessed, however, since our equal temperament is a relatively modern invention. We have very detailed descriptions of these tetrachords (for example, in Harmonics, written by Aristoxenus in the fourth century B.C.), but there is no way of knowing exactly what pitches were being used in them. The enharmonic, chromatic, and diatonic tetrachords mentioned in their descriptions are often now written as in the figure above. But references in the old texts to "shading" suggest that the reality was more complex, and that they probably did not use the same intervals we do. It is more likely that ancient Greek music sounded more like other traditional Mediterranean and Middle Eastern musics than that it sounded anything like modern Western music. One interesting aspect of Greek modes is that different modes were considered to have very different effects, not only on a person's mood, but even on character and morality.

The Medieval Church Modes Sacred music in the middle ages in Western Europe - Gregorian chant, for example - was also modal, and the medieval Church modes were also considered to have different effects on the listener. Each of these modes can easily be found by playing its one octave range, or ambitus, on the "white key" notes on a piano. (They were written this way so that medieval music didn't have to deal with sharps and flats.) But the Dorian mode, for example, didn't have to start on the pitch we call a D. The important thing was the pattern of half steps and whole steps within that octave, and their relationship to the notes that acted as the modal equivalent of tonal centers, the finalis and the dominant.

The modes came in pairs which shared the same finalis. A mode can be found by playing all the "white key" notes on a piano for one octave. From D to D, for example is Dorian; from F to F is Lydian. Notice that no modes begin on A, B, or C. This is because a B flat was allowed, and the modes beginning on D, E, and F, when they use a B flat, sound the same as the A, B, and C modes would. After medieval times, modes beginning on A, B, and C were named, but they are still not considered Church modes. Notice that the Aeolian (or the Dorian using a B flat) is the same as an A (or D) natural minor scale and the Ionian (or the Lydian using a B flat) is the same as a C (or F) major scale. Locrian, on the other hand, is considered to be a theoretically possible but mostly unused mode.

These modes are part of the same theoretical system as the church modes, but they were not used. The tuning system used in medieval Europe was also not our familiar equal temperament system. It was a just intonation system, based on a pure perfect fifth. In this system, half steps are not all equal to each other. This is another reason that different modes sounded very different from each other, although that particular difference may be absent today when chant is sung using equal temperament.

The Ragas of Classical Indian Music The ragas of classical India and other, similar traditions, are more like modes than they are like scales. Like modes, different ragas sound very different from each other, for several reasons. They may have different interval patterns between the "scale" notes, have different expectations for how each note of the raga is to be used, and may even use slightly different tunings. Like the modal musics discussed above, individual Indian ragas are associated with specific moods. In fact, in practice, ragas are even more different from each other than the medieval European modes were. The raga dictates how each note should be used, more specifically than a modal or major-minor system does. Some pitches will get more emphasis than others; some will be used one way in an ascending melody and another way in a descending melody; some will be used in certain types of ornaments. And these rules differ from one raga to the next. The result is that each raga (there are more than two hundred) is a collection of melodic scales, phrases, motifs, and ornaments, that may be used together to construct music in that raga. A good performer will be familiar with dozens of ragas and can improvise music - traditional classical music in India is improvised - using the accepted format for each raga. The raga even affects the tuning of the notes. Indian classical music is usually accompanied by a tanpura, which plays a drone background. The tanpura is usually tuned to a pure perfect fifth, so, just as in medieval European music, the tuning system is a just intonation system. As in Western just intonation, the octave is divided into twelve possible notes, only some of which are used in a particular raga (just as Westerners use only some of the twelve notes in each key). But as was true for the church modes, using the pure perfect fifth means that some "half steps" will be larger than others. (If you would like to understand why this is so, please see Harmonic Series and Tuning Systems.) Even though the variations between these different "half steps" are small, they strongly affect the sound of the music. So, the tuning of some of the notes (not the ones dictated by the tanpura) may be adjusted to better suit a particular raga. (Please see Listening to Indian Classical Music and Indian Classical Music: Tuning and Ragas for more information on this subject.)

Other Non-Western Modal Musics Medieval European chant and classical Indian music are the two modal musics most familiar to the average Western listener. But many other musical traditions around the world are based on modes rather than on scales. (Even some older European folk music is obviously modal.) In some of these traditions, the mode, like the medieval Church modes, tends to be a list of notes used with a specific finalis, which may encourage certain types of melodies. In others, like the Indian raga, is more specifically a collection of related melodies, phrases, and ornamentations. (Some other traditions even use the term raga). But all of these musics have long traditions that are very different from the familiar major-minor tonal system.