Chant is known in modern times as "Gregorian Chant" or "plainchant." It is one of the oldest forms of Catholic music and has long been the preferred companion of the Church's public services. Chant encompasses a wide variety of styles and interpretations; nonetheless, chant is usually easy to recognize by its slow, nonrhythmic lyrics that are sung in unison by all members of the choir. Chant can be sung a cappella or with organ accompaniment. The standard book of chants for the Western Church is the Liber Usualis, which includes an introduction explaining the theory and practice of plainchant according to the Solesmes method.
Sacred polyphony is closely associated with the Italian Renaissance of the 15th and 16th centuries, but its origins can be traced back to the ninth century or even earlier. The term "polyphony" means "many voices," and this is indeed the defining characteristic of sacred polyphony. Polyphonic compositions assign different notes to different members of the choir, introducing harmonies and complex melodies that are absent in chant. Though similar to hymnody, polyphony is distinguished by more intricate patterns of interwoven voices. Also, in polyphony, a single syllable may be held over several notes, or even over an extended melody, whereas hymns usually assign only one note to each syllable.
Hymnody is the technical name for the songs that most people would identify as hymns. Catholic hymnody is extremely diverse and is therefore difficult to characterize. The Catholic Encyclopedia describes hymnody as the "poetry of the people." This description emphasizes that hymns are typically intended to be sung by the average person. Accordingly, hymns tend to contain simpler music and memorable lyrics; this contrasts with the complexity of sacred polyphony, which is performed by skilled choirs. As hymns are the "poetry of the people," it is natural that they are often written in the vernacular. This is a defining characteristic of hymnody, because polyphony and chant are sung almost exclusively in Latin.