One of the fascinating things about music history is how people have gradually over the centuries changed in how dissonance is regarded. From the position that all dissonance was bad and even evil, to the twentieth century view that dissonance can be beautiful, we have accepted and embraced more and more dissonance in our art music. One of my favorite dissonance passages is in William Walton’s oratorio, Belshazzar’s Feast. The choir sings the text “drank from the sacred vessels.” All in quarter notes, “drank from the sa-” is set to minor seconds, “cred ves-“ is set to major seconds, and “sels” is the resolution to a minor third. It is a stunning moment, and sets up a dramatic pause and breath taking phrase. This occurs at 15:02 in the video I’ve included with this post. Listen from 14:14 to 15:52 to get the full effect.
The passage illustrates an important point about music and dissonance. Music is not simply dissonant or consonant. It is not enough that we decide that a sonority is one or another. There are degrees of dissonance, and they contribute degrees of tension. A greater dissonance may be followed by a lesser dissonance, reducing but not eliminating the tension. We hear this in the excerpt from Belshazzar’s Feast as the music progresses from minor seconds to major seconds. The tension and dissonance resolves further when the major seconds are resolved to the minor third. Even with the consonant interval of the minor third, the tension is not completely gone; there are more consonant intervals than a minor third: the perfect fifth and octave. We do not get either of these at this point in the music, so some dissonance remains, even in an interval considered consonant. Just as there are degrees of dissonance, there are also degrees of consonance. Thirds and sixths have some dissonance mixed into them as a result of how the overtones of each interact with each other. A perfect octave has no dissonance, because all overtones are shared by both notes. An untempered perfect fifth also is pure consonance.
Because there are degrees of dissonances and consonances, all must be carefully tuned. If we only tune the consonances, then the dissonances create the intended degree of dissonance, which will usually result in dissonances being too dissonant. Minor seconds and major ninths should have rapid beats audible, whereas major seconds and minor should have slow, pulsating beats audible. Major and minor thirds will both have slow pulsating beats, but minor thirds will also have fast beats at the same time. It is these beats that give the intervals their proper mix of dissonance and consonants. The faster the beats, the more dissonance is involved. The fast beats are sometimes described a roughness.
With training and practice, listeners can develop sensitivity to degrees of dissonance. Starting with highly contrasting dissonances, such as the tritone, which is highly dissonant, and the minor 7th, which is much less so, students can become used to hearing differences in dissonances. Once this sensitivity has been developed, or even has begun to be developed, listening to atonal art music can become much more fun than it was when the student though all dissonances are unpleasant and the same. Listen to “Deserts” by Varese, and focus on the different qualities that various dissonances have throughout the piece. Some of them are quite relaxing, while others make you feel like the bottom just dropped out of your stomach. Being aware of the ebb and flow of the degrees of dissonance will allow you to perceive patterns of stressing and relaxing that make the piece sound less random and noisy, and much more expressive.