Organum

ORGANUM. - The term, which denoted a special compositional technique of at least 2 voices, lies at the origins of polyphony (9th century) and soon came to mean an independent musical form.

Its principal characteristic was parallel or direct motion, in which the voices move while always maintaining the same distance between them (the intervals admitted as consonant were the 4th, 5th and 8th), and it began to decline in the 11th century, when contrary motion (in which the voices draw nearer and move farther apart as they proceed together) was introduced into primitive polyphony and the organum had to give way to the new form of discant (v.). The technical structure of the organum consisted first of all of a pre-existing chant, taken from the liturgical repertory, which was called tenor because it "held" the Gregorian melody (chosen generally from among Graduals, Responsories and Alleluias), and then of other voices that were added above or below the first, at established and regular intervals. In an initial phase the added voice ("vox organalis" or "duplum") was placed below the tenor (or "vox principalis") at a distance of a 4th or a 5th. This form, the simplest, consisted of only 2 voices, was called parallel organum, and lasted throughout the first period in which direct motion is generally practiced; in the 11th century, with the spread of that contrary motion which was already latent in the first phase, in which even the parallel organum began and ended on the unison, there arose free organum, which is already practically a discant, where the voices often come to cross one another. In the 12th century the "vox organalis" passed above the "vox principalis" and no longer follows it note against note, but develops broad melismas, that is, florid groups of several notes, against one note of the tenor. This type of organum, called "purum" or "duplum", widely cultivated especially at St-Martial de Limoges, had as its principal characteristic a great rhythmic freedom in the added voice, while in the following period the rhythmic modes influenced the school of Notre-Dame in Paris (Leoninus and, even more, Perotinus) and set the organum on the path to a clear mensuralism. This was also required by the increased number of added parts which, in Perotinus, reached 3 in the "organa quadrupla". The principal writers who speak of this form are: G. Scotus Eriugena, in the treatise De divisione naturae (c. 877); the author of the Musica enchiriadis (9th century); Regino of Prüm (915); Hucbald in the De harmonica institutione (840-930); Guido d'Arezzo in the Micrologus; the author of the treatise Ad organum faciendum of the Biblioteca Ambrosiana in Milan (11th-12th century); Johannes called Cotton in the De diaphonia (11th-12th century); Elias Salomonis in his Scientia artis musicae, also at the Ambrosiana (13th century). These treatises also offer, in demonstration of the theories set forth, the first examples of organum (v. ARS ANTIQUA; DIAFONIA).

Luisa Cervelli