“Lining out” is a style of psalm-singing in which one singer (the precentor) chants a line of the psalm, and then the congregation comes in and sings the same line. Every singer in the congregation adds grace notes or varies the timing on an individual basis, so instead of a simple melody line it sounds like a swelling wave of sounds. Then, before the first line is done, the precentor starts chanting the second line.

“Lining out” is used in churches that derive from early Calvinism. When much of the congregation was illiterate, it was the only way they could all know what to sing next. This unusual style of psalm-singing survives mostly in two places today- among “Primitive Baptist” churches in the American South, and in the Presbyterian communities of the Scottish Hebrides.

The Gaelic version of lining out has been described as sounding “middle eastern,” with the chanting of the precentor reminiscent of the Moslem call to prayer. It is probably the most unusual-sounding type of music in the entire Western folk tradition. In spiritual terms, the ability to vary the grace notes and the timing gives the worshipers a unique opportunity to express highly personal emotions and religious experiences through the medium of song. Highlanders who grew up with this type of church service have sometimes described the communal singing of the psalms as an ecstatic and transformative experience. The tradition seems to be on the decline along with the Gaelic language itself, but as of this writing it still endures.