Acolouthia

Acolouthia (, "a following"; ) 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.