Saint Gregory the Great was born in about 540 in Rome and was Pope from 590 to his death in 604. He was an intelligent man and effective leader, galvanising the reinforcement of Roman authority in both civil and spiritual matters. He was active in national and international politics, and developed a welfare system including hospitals, charities and more efficient systems of taxation and other branches of the law. Alongside this practical nature, Gregory was a prolific author on the subject of faith and doctrine, recognising the need to present different aspects of Christian belief in as clear and unambiguous a manner as possible. This in turn enabled Christian missionaries to travel the world with a consistent message.

Gregory consolidated the Church of Rome by instituting more uniform worship, absorbing different Latin liturgies (Gallican, Mozarabic or Old Hispanic, Ambrosian, Celtic) into the Roman liturgy. The musical tradition was still primarily aural (learned by ear) and not generally written down, but when notation, in the form of neumes, began to be more widely used in about the 10th century, there was widespread agreement as to the shape of that worship. Even so, Gregory’s involvement with music has been exaggerated thanks to a legend that developed in the 9th century concerning his supposed authorship of the chant; this would lead to the adoption of the term ‘Gregorian chant’. The main source of this myth seems to have been Johannes Hymonides, known as John the Deacon of Rome, who in 875 wrote a biography of Gregory crediting the pope with compiling the antiphoner (volume of chants). In reality, although Gregory founded a Schola Cantorum or music school in Rome, his contribution to the nature of the chant was limited only to his liturgical reforms, which helped to consolidate musical practices within the Roman liturgy.

During the Carolingian dynasty, Charlemagne (748-814) sought to unify the Frankish church according to Roman practices. This unification of different liturgies was politically expedient, but was also driven by Charlemagne’s faith and reverence for Rome. Prior to this, the Roman rite was just one of many liturgies. Charlemagne explicitly called for the marriage of different chant traditions, especially Gallican chant and Roman chant. This hybrid of Gallican and Roman forms was called Carolingian chant: essentially Old Roman, but with traces of Gallican chant remaining. This in turn came to be known as Gregorian chant, thanks to the enduring legend of Gregory’s authorship.

Gregorian chants were notated using neumes, the precursor to today’s staffed notation. The earliest neumes were roughly sketched markers to indicate the overall shape of a melody rather than a specific set of notes. This system was refined to become a more precise representation of pitch.

Gregorian chants are organised into different modes, the precursor to the modern concept of key. Today, Western music is often divided into two main modes: major and minor, with an array of keys falling into those two categories. Gregorian chant is generally divided into eight modes. All modes are characterised by their intervals; by how big a musical ‘distance’ is between each note, usually a whole tone (such as C to D) or the closer, smaller interval of the semitone (such as B to C, or C to C-sharp.) The eight modes were widely used between the 8th and 16th centuries. Gregorian modes are divided into authentic and plagal modes:

Protus
Dorian

Deuterus
Phrygian

Tritus
Lydian

Tetrardus
Mixolydian

The final or principal pitch of the authentic modes is the tonic. The tenor or dominant is usually the interval of a fifth above the final.