**ARs NOVA.** – This term designates the movement of renewal in sacred composition that animated polyphonic music from the early years of the 14th century to the early 15th century. While it advanced the progress of notation (v.) by introducing binary time in place of ternary time and creating small note values—minim, semibreve, crotchet, and quaver—originating from the instrumental practice of dance pieces and the technical virtuosity of vocal pieces, it also marked the beginning of the secularization of church music. This secularization, expressed in the growing detachment from Gregorian chant, culminated in the rich Flemish contrapuntal architecture of the 15th century, built on popular themes, and was only curbed two centuries later by the Council of Trent, which advocated a return to Gregorian chant, either as direct performance or as inspiration for polyphony.
Of the two major groups of sources—treatises and monuments of practical music—the first is notably sacred in comparison to the second, especially when considering the vast corpus of treatises from the preceding period, i.e., ars antiqua (v.). The first decisive step toward the ars nova is found in the writings of Marchetto da Padova, who, after the *Lucidarium in arte musicae planae* (1274), composed around 1300 the *Pomerium artis musicae mensurabilis*, in which he illustrates, among other things, the new Italian notation. Shortly thereafter, around 1325, we encounter the famous treatise by Philippe de Vitry, titled *Ars nova*, a term also used in the writings of his friend Joannes de Muris: *Ars novae musicae*, which gave its name to the entire movement. Aside from other minor treatises still unpublished by some masters of musical practice (including Jacopo, Paolo, and Zaccharias), we may finally cite the great fellow citizen of Marchetto, Prosdocimus de Beldemandis, who in his *Tractatus practicae de musica mensurabili ad modum Italicorum*, written about a century later (c. 1410), provides a retrospective view of the 14th-century Italian notation foreshadowed by Marchetto. The two Paduan theorists may therefore be considered, in a broad sense, as the boundary points between which the musical world of the Italian ars nova moved and operated.
From a practical standpoint, sacred music in this period lacks the great liturgical cycles that, in the ars antiqua, accompanied the unfolding of the ecclesiastical year. The mere five or six parts of the Ordinary of the Mass that are now set to music appear to be composed under the direct influence of the five prevailing forms: the motet, the French *ballade*, the *conductus*, the madrigal, and the *caccia*. Thus, we have three important cycles of the *Ordinarium*: the Tournai Mass, in three voices, still very close to the 13th century in its modal rhythm and notation; the Mass of G. Machaut, in four voices, one of the earliest examples of the genre, both composed in the style of the *conductus*; and finally, a collection of authors from northern and central Italy (Paris, ital. 568), which, together with another smaller collection of Romagna origin (Vat. Urb. 1419), provides some significant examples of 14th-century Italian art. Of the surviving French ars nova repertoire, two famous manuscripts from Avignon (first half of the 14th century), now in Ivrea and Apt, contain motets and masses in the style of the secular motet, the *conductus*, the French ballade, and, among other works (in Ivrea), a Credo in that isorhythmic form which the great poet-musician Machaut favored to realize, in his motets, the principles of Ph. de Vitry. Although ecclesiastical music of this period was present and rich in various countries to accompany liturgical ceremonies, it was nonetheless so pervaded by secular elements that invaded the field of music as to compel Pope John XXII (1324–25) to raise his voice against the abuses that diverted sacred song from its true liturgical office of reverence and invitation to prayer.