Akolouthia

Acolouthia (Greek: ἀκολουθία, "a following"; Slavonic: posledovanie) in the Eastern Orthodox and Eastern Catholic churches, signifies the arrangement of the Divine Services (Canonical Hours or Divine Office), perhaps because the parts are closely connected and follow in order. In a more restricted sense, the term "acolouth" refers to the fixed portion of the Office (which does not change daily). The portions of the Office that are variable are called the Sequences. While the structure and history of the various forms of the Divine Office in the numerous ancient Christian rites is exceedingly rich, the following article will restrict itself to the practice as it evolved in the Eastern Roman (Byzantine) Empire.

The Office is composed of both musical and rhetorical elements, the first usually given in the musical mode or tone (echos), according to which the liturgical compositions are chanted. There are eight musical modes: four primary and four secondary (plagal). The rhetorical elements are seldom given in a normal speaking voice, but are "read" in a simple recitative.

As the early chanters rarely used texts set to musical notation, they learned by heart the words and music of some standard hymn, and this served as a model for other hymns of the same rhythm or meter. For example, in a Canon, the strophe or stanza of a standard hymn which indicates the melody of a composition is known as an irmos (eirmos, hirmos). An irmos is placed at the beginning of an Ode to introduce the melody to which it should be chanted, and to tie the theme of the Biblical Canticle on which it is based to the hymns of the Ode that follow (see Canon). A katabasia is the irmos that is sung at the end of an Ode by the choir (which descend from their seats (kathismata) and stand on the floor of the church to sing it). The katabasia winds down the Ode and returns it again to the theme of the Biblical Canticle.

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