It is a short piece of plain-song introduced before a psalm or canticle, to the tune of which it corresponds, while the words are selected so as specially to illustrate and enforce the evangelical or prophetic meaning of the text.
The connection of the music of the antiphon with that of the psalm is explained by Durandus from the etymology of the term – ‘because antiphons are as keys and indices according to the modulation and sound of which the following canticle or psalm is sung alternately. For the tone of the whole psalm is taken from the tone of the antiphon.’
Antiphonal or alternate singing, as in the chanting of psalms verse by verse – or by half verse, as head by Mendelssohn in Rome during the Holy Week – is of very high antiquity.
It was characteristic of the Hebrew and early Christian worship, and is mentioned by Philo in the middle of the first century, describing the Tuerapeutae, and has always been more or less practiced in the Church.
The French term ‘antienne’ and the English ‘anthem’ are derived from antiphon, probably in reference to each of the meanings given above, as an independent piece of music sung from side to side of the choir.