Music Theory/Plainsong

Plainsong is a form of music that originated in Christian churches early in the church's history. Christians wanted to praise God in a special way, and so chose to sing the entire liturgy when they held services. At first, with archaic and variant practices, such early plainsong was linked to specific communities and based on folk melody. However, as specific forms of liturgies were cemented, particularly the Liturgy of St. John Chrysostom, the Liturgy of St. Basil, and the Liturgy of Pope Gregory I (the Mass), plainsong grew to be a formalised and integral part of christian worship.

Notable Features

Plainsong is characterised by a number of key features:

Sonority and Instrumentation

It is usually unaccompanied. The phrase "a capella" literally means "from the chapel/church", and implies an unaccompanied texture. In a modern context, sometimes instruments such as the organ can provide basic harmonic support, but this is minimal and very rare.
It has a reasonable range. As it is designed to be sung by anyone and everyone in a church congregation, the range of notes for a particular piece of plainsong rarely exceeds one octave, and it is not very virtuosic.

Melody

It is melody-driven. At its root nearly all plainsong is a single monophonic line.
It is scalic. Where there are leaps, they are at most a perfect 5th. Most plainsong is dependent on scalic motions.
It can be very ornate. Melismas on particular words are very common.

Harmony

As plainsong is typically unaccompanied, harmony does not apply. Where harmony is used by certain traditions, it is block homophony, and quite simple.
Pedal notes and drones are sometimes used to underpin the melody.

Tonality

Plainsong used all modes available, with 8 identified for primary use, and 4 others used archaically.

Texture

Monophonic. A single solo melodic line is ubiquitous.
Homophonic. In certain traditions, harmony (or pedals and drones) are used as a basic accompaniment. The melody drives this.

Structure

Strophic. The earliest plainsong hymns (as an example, Tantum Ergo by Thomas Aquinas) are based on repeated verses.
Through-composed. Most plainsong is simply designed to match the words, so melodies are not repeated.

Tempo, Rhythm, and Metre

Tempo is at natural speech rhythms. In a modern context, plainsong is often sung quite slowly, but it can be sung at a very fast pace.
Metres were non-existent when plainsong was written. This was in favour of natural speech rhythms.
Rhythms are simple, mainly to do with lengthening certain syllables with longer notes for emphasis.

Composers

It is often difficult to pin down exactly who wrote each piece of plainsong. Certain authors of texts, such as St. Thomas Aquinas, are well recognised. Ironically, even though plainsong is often all painted under the brush "Gregorian chant" it is difficult to categorically say whether Pope Gregory I wrote any plainsong at all. Other composers are know. Hildegard of Bingen is known for her developments based on plainsong. Many composers have been known to use plainsong in their liturgical works.