AGGREGATES - According to the Slavonic Typicon, the different Canonical Hours (including Midnight Office and Typica) may be grouped together into aggregates so that there are three major times of prayer a day: Evening, Morning and Midday. This is to conform with Psalm 55:17, "Evening, morning, and noonday will I tell of it and will declare it, and He will hear my voice." While the aggregations will vary depending upon the liturgical season, the most common groupings are as follows:

• Evening—Ninth Hour, Vespers

• Morning—Midnight Office, Matins, First Hour

• Noonday—Third Hour, Sixth Hour, Divine Liturgy (or Typica )

On the eves before Great Feasts and Sundays in some traditions, Vespers, Matins, and the First Hour are served together in an aggregation called the All-Night Vigil. In other traditions it is more common for the Ninth Hour and Vespers to be served separately the evening before, and for Matins to be served in the morning before the Liturgy. Some Great Feasts prescribe a Vesperal Divine Liturgy to be served on the afternoon before; in these cases, Great Compline is substituted for Vespers during the All-night Vigil.