The Pope has called for a revival of the sacred music of the church's past. After folk and rock 'n' roll Masses, what will the faithful make of polyphony, asks Aengus Collins

Earlier this summer a concert in the Pope's honour was held in the Sistine Chapel. Presented by Domenico Bartolucci, a former director of the Chapel's choir, it was an evening of polyphony featuring compositions by Palestrina and by Bartolucci himself. For centuries, polyphony has been at the core of the church's musical traditions, but in recent decades its standing has suffered and pallid alternatives have taken its place at the heart of Catholic worship.

Bartolucci's return to the Sistine Chapel was significant in its own right. He had been appointed perpetual director of the choir in 1956, but this lifetime appointment was cut short in 1997 when he was replaced by Giuseppe Liberto. A favourite of John Paul II, Liberto had a reputation for trying to make sacred music more accessible.

Within the Vatican, the most prominent dissenter from the decision to remove Bartolucci was Cardinal Ratzinger, now Pope Benedict XVI. So it is perhaps fitting that the pontiff chose Bartolucci's concert in his honour as the moment to make a call for a revival of the music of the church's past.

Speaking after the concert, he said: "All the passages we have heard - and especially the performance as a whole in which the 16th and 20th centuries run parallel - together confirm the conviction that sacred polyphony, particularly that of the so-called 'Roman School', is a legacy to preserve with care, to keep alive and to make known . . . An authentic renewal of sacred music can only happen in the wake of the great tradition of the past, of Gregorian chant and sacred polyphony."

The golden age of sacred polyphony was during the Renaissance, but the music has its roots many centuries earlier in Gregorian chant and its earliest harmonising variant, organum. As early as the ninth century, the Irish theologian and philosopher John Scotus Erigena was writing of polyphony's unique capacity to give musical form to the beauty of cosmic harmony.

One of the key characteristics of sacred music is its use of melisma, which involves the elongation of individual syllables of sung text to accommodate numerous changes of pitch. It's what gives the music its fluid feel. Gregorian chant is melismatic, but only one melody is sung. The story of the evolution of sacred polyphony is one of increasingly sophisticated innovations being layered above the monophonic chant line.

Initially, in the eighth and ninth centuries, the changes introduced were modest. A second voice was added above the tenor chant, but carefully so as to ensure that any harmonising occurred at perfect intervals - to have done otherwise would have been to worship God by imperfect means.

Over the centuries, however, the musical additions and embellishments became more adventurous. Increasing numbers of vocal parts were interwoven above the chant line. More controversially, secular elements were introduced - secular texts were sung above the chant, and the liturgical texts were set to secular melodies. Gradually the liturgical basis of the music became less and less prominent.

Polyphony has unavoidable religious connotations for us today. It sounds like church music. But in the early 14th century, as the form was starting to mature, it was seen by some as shockingly irreligious. Pope John XXII prohibited the liturgical use of polyphony, and spoke out against it in the 1324 bull Docta Sanctorum Patrum: "[ T]he mere number of the notes, in these compositions, conceal from us the plain-chant melody, with its simple, well-regulated rises and falls . . . These musicians run without pausing, they intoxicate the ear without satisfying it, they dramatise the text with gestures and, instead of promoting devotion, they prevent it."

But John was fighting a losing battle, and 40 years later Guillaume de Machaut became the first person to compose a polyphonic setting of the full Mass. Sacred polyphony went from strength to strength in the years that followed, and the work of composers such as Josquin, Palestrina and Lassus made it one of the crowning artistic achievements of the Renaissance era.

Lingering doubts about its liturgical appropriateness remained, however. In the mid-16th century, the Council of Trent said that musical developments had gone too far, and called for a return to music that would preserve the clear intelligibility of liturgical texts. Palestrina is credited with overcoming the Council's reservations by developing a smooth, refined polyphonic style that has remained the model of musical perfection in the Catholic Church.

In subsequent centuries sacred music has become an increasingly secular activity. The religious works of the great classical composers - such as the Masses of Mozart, Haydn and Beethoven - are more at home in concert halls than churches. In 1903, Pope Pius X issued detailed instructions about the proper liturgical uses of music. He called for a return to chant and polyphony, and singled out the 19th century's "theatrical" styles of composition as being unfit for use in church.

In more recent years compositions of sacred music have become less dramatic, less ornate. One thinks of composers such as Górecki, Pärt and Taverner - the so-called holy minimalists - who have been hugely successful with works that sound much more traditionally sacred than do many of their classical predecessors. It is something of a paradox that atheist Europe seems to feel quite comfortable with the traditional textures of sacred music.

This is not what Benedict is concerned with, however. His problem isn't with the development of sacred music outside the church but with its decline inside the church.

As with many current disputes in the Catholic Church, debates over the role of music stem from the reforms of Vatican II. On paper the council was uncontroversial on musical matters, giving chant and polyphony their customary pride of place. But Vatican II was a reforming council, and it was perhaps inevitable that its reforms would spread to music. As the language of the Mass shifted to the vernacular, so too did the music. Congregational involvement was increasingly encouraged, and chant and polyphony gave way to music that was supposed to be easier to relate to. The results have frequently been mawkish and banal, though, and recent innovations have included folk and rock Masses.

The question Benedict was addressing with his recent comments in the Sistine Chapel was whether too much has been sacrificed by the changes that followed Vatican II. In purely musical terms, the answer is surely yes. Palestrina's pre-eminence hasn't been challenged by the music of the past four decades, to say the very least. But of course this is not a purely musical question. It's a matter of church politics and of attitudes to tradition and reform. While sacred music flourishes free of baggage in the concert hall, within the church it seems now to have become a lightning rod for responses to decline.

This is highlighted by reactions to the Pope's comments. Cardinal Ersilio Tonini lined up behind Benedict saying: "Mass is the presence of Christ and the music adds so much more when the harmony allows the mind to transcend the concrete to the divine." But Cardinal Carlo Furno took a different line, suggesting that "it is better to have guitars on the altar and rock'n'roll Masses than empty churches".

Seen in these terms, the question of sacred music is one on which Benedict was always going to take a traditionalist line. His vision of a "mustard seed" church - small in size but uncorrupted - suggests that he is reconciled to significant decline within the Church, and unconvinced by the wisdom of compromising in an effort to boost numbers. Polyphonic music is part of the core tradition of Catholic worship, he seems to be saying, and if reviving it entails driving away a proportion of the congregation, then so be it.