The plot thickens:
http://www.ubieta.com/bimodalism/'Pietro Raimondi’s Esempio No.4, from Due Fughe In Una (1849) for two mixed choruses and organ, cannot be considered a case of early Bimodalism in history, as the composer consciously eludes the simultaneity of both thirds on the modal degrees of the work in question.
As Raimondi admitted, "Molto difficile mi è riuscito questo esempio, per causa delle terze ora maggiori, ed ora minori, secondo le circostanze, onde non guastare il canto." [This example has been quite challenging for me, first in handling the major third, then the minor, such that the singing would not be impaired in any case.]
His procedure was ingenious: As one chorus sings in D major, the other sings in D minor, neither chorus coinciding harmonically in the modal thirds throughout the piece.'
