It is essential to be clear exactly what is meant by ‘polychoral’. The following definition is suggested as being consistent with sixteenth-century theory and practice: a polychoral work or passage is one in which the ensemble is consistently split in to two or more groups, each retaining its own identity, which sing separately and together within a through-composed framework in which antiphony is a fundamental compositional resource; in tutti passages all voiceparts should normally remain independent, with the possible exception of the bass parts. Thus most Anglican cantoris-decani practice does not come within the definition, being more of a kind of antiphonal divisi technique. Polychoralism usually lies within the realm of technique or style rather than genre, though there are exceptions to this where the liturgical format of, for example, psalms or canticles is strictly adhered to. My approach to the phenomenon is primarily as a compositional technique; the question of performing locations and spatial separation will be treated mainly in terms of its refiection in the technique of individual pieces.
CARVER, Anthony F.. Cori Spezzati – Volume 1 – The development of sacred polychoral music to the time of Schütz. Cambridge: Cambridge University Press, 1988, p. xv.