When I was a high school student, I was sure I knew what dissonance in music was. If it sounded wrong, it was dissonant, and if it sounded right, it was consonant. An interval of a 2nd, or a try tone, or a seventh was dissonant, and all the others were consonant. Then in college, I learned that a perfect 4th is dissonant, though it still sounded fine to me. But that was the first hint that something was amiss with my definition. If an interval that sounded right to me was dissonant, then I needed a new understanding of the concept. In my discussion of expectations (see “Is All Music Intended to Be Expressive?”), I mentioned Meyer’s thoughts on continuance and repose. Music that demands continuance, or “leaves us hanging” creates tension, whereas music that comes to rest harmonically, as at a full cadence, expresses repose or relaxation.

Once of the expectations Western listeners have is that tension will resolve into relaxation. We are accustomed to patterns of tension and relaxation in our music. This is the basis for traditional voice leading and harmonic progressions. Ornaments such as suspensions, appagiaturas, trills, and so forth create tension because they sound incomplete, as one who stops in the middle of a sentence. We know from our experience with grammar that there has to be more to that sentence, and we know from our experience with music that there has to be more to that musical phrase, more music that will bring us to that cadence, that musical punctuation of a comma, semi-colon, or period. It is that expectation, even necessity of the music continuing on to a more suitable pausing or stopping place that makes the present moment sound dissonant.

In framing dissonance in this way, I am essentially equating dissonance with continuance. The unresolved suspension is not dissonant because it sounds “wrong,” it sounds dissonant because it leaves us demanding more. Dissonance is unfulfilled expectation. It is a form of anxiety similar to what we experience when we worriedly await the outcome of some life event. That anxious, stressed feeling is akin to how our body reacts to dissonance in music.

Zatorre and Blood (1999) at McGill University created original melodies containing dissonant and consonant patterns of notes, and played them for ten volunteers who were  scanned at the same time. Rejecting the null hypothesis, dissonance made areas of the limbic system linked to unpleasant emotions light up in the PET scans, whereas the consonant melodies stimulated limbic structures associated with pleasure. In other words, music elicits the same emotional response in the human brain as non-musical events with the same emotional makeup. So our experience of dissonance is larger than a response limited to musical stimuli. Our perception of musical dissonance is a parallel response to other life experiences.

In The Harvard Dictionary of Music we find that dissonance represents the “element of disturbance and tension.” While tension can, as we have seen, be framed within unsatisfied or delayed expectations, disturbance is a dangerously subjective idea. Listeners are disturbed by different sounds to different degrees. We must also consider that what was once considered dissonant to musicians and audiences alike are now accepted as less so or even consonant now. There is a phrase in Walton’s Belshazzar’s Feast in which the choir sings the text “drank from the sacred vessels.” “Drank from the” is set to a minor 2nd, “sacred ves-” to a major 2nd, and “-sels” to a minor third. Though the 2nds are by some definitions dissonance, they are to my ear delectable and beautiful in the sense that the imminent resolution is so quickly realized and from the extreme “disturbance” of the minor 2nd. In this, we might consider that dissonance may be determined in part by its duration prior to its resolution. The longer the disturbance remains, the more likely it is to be perceived as dissonance. Dissononances that occupy short time spans may be less apt to be perceived as dissonant because they are more closely associated or attached to their resolutions. This is why a suspension can seem more consonant than an escape tone, wherein the resolution by skip obscures the tranquility of the resolution.

Some have attempted to define dissonance as any interval not included in the prevailing diatonic scale.  As long as diatonicism is the standard for measuring consonance or dissonance, this definition is at least serviceable. But it is rendered inappropriate for atonal works. Hindemith (1900) breached this issue by putting forth a ranking of melodic intervals from most consonant to most dissonant. This ranking was P5, P4, M6, M3, m3, m6, M2, m7, m2, M7, TT. Hindemith believed that consonance and dissonance could be perceived as a kind of floating standard, constantly defined by the current interval regardless of overall tonal center or lack there of. Still, there are vestiges of traditional harmony in his ranking, because the first 4 intervals are all diatonic and all part of the tonic, dominant, or subdominant chords. Hindemith believed that we shifted our perception of tonal center according to intervallic relationships when interval roots were non-diatonic.

This theory allowed for writing in the 12-tone style without abandoning tonality. Tones that are lowest, highest, and longest are given greatest importance in a melodic progression. These tones then are constructed to form step-wise motion, no matter their separation from one another by intervening tones. The interval of the fifth, being the most consonant, is also the strongest harmonically. It’s occurrence over changing roots can thus alter the perceived tonal center, whereas intervals gradually loose their ability to establish tonal centers according to their increased property of dissonance. To state it in terms of our overall discussion, the perfect 5th has the least power of continuance and the highest degree of repose, and so functions as a tonic in traditional harmony. As intervals become more dissonant, they gain greater power of continuance and lessening degrees of repose, and so add tension as well as distance from a perceived tonal center. Listen to this example from Hindemith, and see how much of our discussion you can take away.

Blood, A. J., Zatorre, R. J., Bermudez, P., & Evans, A. C. (January 01, 1999). Emotional responses to pleasant and unpleasant music correlate with activity in paralimbic brain regions. Nature Neuroscience, 2, 4, 382-7.

Hindemith, P. (1900). The craft of musical composition. Mainz: Schott.