There’s something hauntingly beautiful about a Gregorian chant. Despite the limited knowledge in medieval times of essential musical concepts such as harmony, tonality and rhythm, somehow the Gregorian chant manages to transport the listener to another world, a different time, not merely by its ancient sound but also by its ability to create the sense of approaching something special.
Music has come a long way since then, but not without the cumulative advances of countless musicians over the course of history. How exciting it must have been to discover new musical concepts or techniques that we take for granted today!
Something as simple as oblique motion, where one voice repeats a note while another voice simultaneously moves in melodic motion, was revolutionary! We see one of the earliest surviving examples of oblique motion in Rex caeli domine maris, an anonymous Gregorian chant found in a 10th-century music handbook, Musica enchiriadis.
This video begins with the chant as it appears in the handbook, with its primitive form of music notation, and also transcribes sections into more modern-looking notation.
At 01:36 in the video you come across more modern notation of the oblique motion, but listen to the whole chant from the beginning in order to better hear the impact of the oblique motion in its surrounding contexts.
What really strikes me about the function of the oblique motion here is not so much that it provides a basic harmonic accompaniment, but rather that its presence heightens the ascent of the other voice.
Note that the top voice begins by ascending from middle C to G, in a C major-like pentascale, while the other voice briefly repeats middle C below it, giving the sense of the melody pulling away, thus intensifying our auditory perception of the ascending motion.
It’s like the difference between watching an airplane’s ascent in the middle of the sky and watching it pull up off the tarmac. The latter intensifies the airplane’s ascent by giving us a visual of it pulling away. Oblique motion can do the same thing in music with an ascending melodic line, particularly when starting from the same pitch or the same note. Conversely, in a descending line, it can heighten the sense of closing the gap.
Next time you come across oblique motion in a piece of music, play the lines separately, then together, to experience the impact on your auditory perception of the other musical voice!