Really skillful British extemporizers, going all the way back to the time of Giraldus Cambrensis,
could come up with much more impressive harmonizations, not only in three parts but in four or even
more. Desiderius Erasmus (Erasmus of Rotterdam), the great humanist scholar and a great Anglophile,
reported in amazement, following one of his many visits to England toward the end of the fifteenth century,
that in English churches “many sing together, but none of the singers produce those sounds which the notes
on the page indicate.” (This sounds a lot like Giraldus, in fact, except that the Welsh singers he described
did not use books at all.)
We can share in Erasmus’s amazement if we travel forward in time a bit for a quick look at the latest
and most advanced treatise on supra librum singing from the British Isles. A manual copied in Scotland
around 1580, but summing up two or three hundred years’ worth of singers’ lore, ends with a final chapter
on “countering” in which twelve rules are given that, when mastered over considerable time, enabled a
quartet of singers to take a simple line of plainchant (like Ex. 11-22a) and from it work up on the spot a
polyphonic realization like the one shown in the treatise’s final didactic example. The tenor sings a highly
embellished version of the cantus firmus at the original pitch (each measure beginning and ending with the
notated pitch, but with the middle filled most fancifully), and the other parts carol away even more
ornately, albeit according to strict—and, no doubt, well-kept—secret formulas (Ex. 11-22b).
EX. 11-22A Heir beginnis countering, presumed cantus firmusEX. 11-22B Heir beginnis countering, final example, mm. 1–6