Modes
The term modal is generally used when describing music written before the major and minor scales became pre-eminent, that is, music from approximately 300 AD to 1600 AD. The modes have a different arrangement of tones and semitones to the major and minor scales, but there is a great deal more to modal music than this superficial difference. For well over a millenium the modal system provided the foundation from which plainsong (also known as chant) and much folksong was created. Plainsong is unaccompanied melody, seemingly simple because of the limited choice of notes available in a mode, yet complex because of the huge variety of melodic and rhythmic patterns which were created with that limited pallette. The early composers of plainsong were typically monks who believed that music should bring the faithful closer to God, and was therefore to be used for ceremonial and ritualistic purposes (for example, around 750 AD St. John Damascene of Damascus was composing groups of hymns which were used in an eight-week cycle for church services. Each group was written in one of the modes; a group would be sung for a week, the following week a group in the next mode would be used, and so on, so that after eight weeks the modal cycle would begin again with a fresh set of hymns).
The ecclesiastical modes (also called traditional or church modes) differ from the modern major and minor scales not only in their disposition of tones and semitones, but also in the way that certain melodic patterns or formulae tend to be associated with a particular mode (in medieval Russian chant the first mode has approximately 90 of these patterns). The patterns are somewhat subtle, but are important. The same principle is apparent in blues and jazz, in which there are many idiomatic figurations (usually called riffs) that are used by experienced musicians to give the 'authentic' sound to the music. (This is why virtuoso 'classical' players who may be familiar with the basic structure and harmonic materials of blues often play this style unconvincingly - they don't know the 'riffs' and how to combine or develop them stylistically.)
The following tables show the basic structure of the modes. The range column refers to the 'white' notes on the piano which encompass one octave of the mode. For example, the range of the Dorian mode is specified as d to d' (from d to the octave above), therefore the notes of the Dorian would be as in figure 1. Of course the mode can be transposed to any pitch, so the Dorian mode can be based at C as in figure 2.
| figure 1 | figure 2 |
|---|
 |  |
The T/S grouping column shows the disposition of tones and semitones in the same way as was explained for the major scale on the Scales page.
| mode | range | T/S grouping |
|---|
| Dorian | d - d' | T S T T T S T |
| Phyrgian | e - e' | S T T T S T T |
| Lydian | f - f' | T T T S T T S |
| Mixolydian | g - g' | T T S T T S T |
| Aeolian | a - a' | T S T T S T T |
| Ionian | c - c' | T T S T T T S |
The Aeolian and Ionian modes were later additions to the theory of the modes. The Aeolian is identical to the 'natural' minor (the descending harmonic minor) and the Ionian is the same as the major scale.
The following table shows the system of eight modes as given in the oldest theoretical references (beginning around the ninth century AD). This includes the 'plagal' forms of the modes, which have the prefix Hypo. The plagal version of a mode starts a 4th below the 'authentic' version. The 'final' is the note on which the plainsong typically ends, the 'dominant' is a note which is next in importance to the 'final'.
| mode | Latin name | final | range | dominant |
|---|
| Dorian | Protus authenticus | d | d - d' | a |
| Hypodorian | Protus plagalis | d | A - a | f |
| Phrygian | Deuterus authenticus | e | e - e' | c' |
| Hypophrygian | Deuterus plagalis | e | B - b | a |
| Lydian | Tritus authenticus | f | f - f' | c' |
| Hypolydian | Tritus plagalis | f | c - c' | a |
| Mixolydian | Tertrardus authenticus | g | g - g' | d' |
| Hypomixolydian | Tertrardus plagalis | g | d - d' | c' |