In Jerry's post above about improvisation, where he talks about stock phrases dropped into various songs, these come from the "floating" verses found in negro spirituals. As an antiphon, a verse, or a response, these were the items used to flesh out a song for singing in the fields at work, to keep a rhythm going and pass the time in an uplifting way... they were frequently made up of Bible images, whether they had anything to do with the theme of the song as first tossed out by the song leader or not. (This need for rhythm, by which to do repetitive, exhausting work as painlessly and efficiently as possible, is not unlike the way sea chanteys came to be. You can still hear this in later black gospel where even a long, improvised testifyin' carries a strong relationship to the beat.)

Other spirituals were done not at work, but as a "shout" where the singers would march together in the grip of the spirit, chant/singing in time to the movement, often very repetitively and often with floating verses contributed as leadership of the shout moved around among participants.

Sometimes the floaters would present a contrasting theme to the main theme which would occur in a refrain that would open as well as punctuate the piece, and sometimes they would be a couplet sung back to the leader as the leader took the song through a story or a topic, in the call/response pattern. You hear these in black gospel, too, throughout all its many styles over the decades, as well as in current black gospel sung in church worship.

~Susan