A tonary is a liturgical book in the Western Christian Church which lists by incipit various items of Gregorian chant according to the Gregorian mode (tonus) of their melodies within the eight-mode system. Tonaries often include Office antiphons, the mode of which determines the recitation formula for the accompanying text (the psalm tone if the antiphon is sung with a psalm, or canticle tone if the antiphon is sung with a canticle), but a tonary may also or instead list responsories or Mass chants not associated with formulaic recitation. Although some tonaries are stand-alone works, they were frequently used as an appendix to other liturgical books such as antiphonaries, graduals, tropers, and prosers, and are often included in collections of musical treatises.