says that what God was, God remains, the word permansit is stretched out for an “eternity.” And where
the text says that what man was not a man shall assume, the word assumpsit is “painted” according to its
etymological meaning, by strange rising intervals—an octave in the soprano, a minor sixth in the tenor,
and a weird augmented second (normally forbidden by “nature”) in the bass.
EX. 18-9A Jacobus Gallus, Mirabile mysterium, mm. 1–11But the most esoteric musical effect is reserved for the moment of mystery: the preternatural passing
of the one substance into the other “without mixture” calls forth a possibly unprecedented triple chromatic
inflection, disguised by false relations (Ex. 18-9c). On passus the bass’s B is inflected to B both by
direct progression and by transfer to the soprano; The alto’s D# is inflected to D-natural by transfer to the
tenor; and the soprano’s F# is inflected to F-natural by transfer to the alto. In the process both soprano and
alto sing intervals (diminished fourth and diminished third respectively) that do not exist at all within the
rules of the ars perfecta. More “innovations of nature.” Simply “side-slipping” from a B major to a B
major triad would not have conveyed the “marvelous mystery.” What makes it marvelous and uncanny is
the way in which the voices all exchange their positions in passing between those two mutually exclusive
harmonies. That exchange, to quote another mystical Christmas antiphon, is truly an admirabile
commercium: a dazzling interchange. To account for the musical effect takes a musician; to discuss the
mystery takes a theologian; but the uncanny experience is available to all through sheer sensory
perception.