2.23 Dissonance

In tonal music, a dissonance is a tone that requires resolution . Dissonances cannot be goals of motion: Instead, they demand continuation .

For this reason, dissonances promote flow : They keep the music moving forward. For instance, listen to this excerpt from Joseph Haydn’s The Creation . Haydn’s goal in this passage was to musically depict the first sunrise of Genesis. Stripped of its dissonances , the harmony lurches from one chord to the next.

Now listen to how the dissonances , by connecting one chord to the next, contribute to the sense of the sun’s steady ascent and brightening.

Dissonance has other important functions. Polyphony refers to voices moving independently. Dissonance promotes polyphony by enabling voices to reach chord tones at different times. In this excerpt from the slow movement of Felix Mendelssohn’s Italian Symphony, the strings play the melody.

In the return of the theme, Mendelssohn offsets the winds, creating a string of dissonances .

In this excerpt from Anton Bruckner’s Symphony No. 8, ,the oboe delays its motion, creating a string of dissonances with the rest of the instruments.

Dissonances also promote independence by enabling musical lines to move at different speeds within the same harmony . In this excerpt from Peter Ilyich Tchaikovsky’s ballet The Nutcracker , the melody is initially presented with a crisp, homophonic accompaniment. When the melody is repeated, dissonance enables the violas to add a fast-moving line within the same harmonic progression.

Dissonance is also used to heighten the expressivity and tension . Arnold Schoenberg’s instrumental tone poem Transfigured Night tells the story of a woman who reveals to her lover that she is carrying the child of another man. As she unburdens herself, Schoenberg heightens the pathos with dissonance .

In the Academy Award winning film On the Waterfront , the mobster lawyer Charley Malloy must decide whether to kill his brother Terry to keep him from testifying against his bosses. As he heads towards a fateful meeting with his brother, Leonard Bernstein underscores Charley’s predicament with two highly dissonant chords .

Consonant chords are perceptually “transparent:” It is easy to “hear into” the chord and analyze its components.

Here is a Major chord:

Which of these pitches doesn’t belong?

Here is a minor chord:

Which of these pitches doesn’t belong?

In both cases, you probably found it easy to pick out the “wrong” note.

Dissonance creates harmonic opacity . It makes chord identification more difficult: It is harder to distinguish the constituent sounds.

Here is a dissonant chord from Olivier Messiaen’s Vision de l’Amen.

Which of these pitches doesn’t belong?:

This time, you were probably less confident of your answer!

Charles Ives humorously illustrates the difference between perceptual transparency and opacity in his short piano work Bad Resolutions and Good.

As when Romeo and Juliet first meet while masked or a murderer hides among the guests in a whodunnit, dissonance can enable musical content to be artfully concealed, obstructed or rendered out-of-focus. Dissonance and chromaticism combined together ratchet up the opacity . Here is the main subject from Contrapunktus IX from J.S. Bach’s Art of the Fugue presented alone:

In this excerpt, the subject is in a lower register, with other lines added above it. Thanks to the largely diatonic harmony and limited role of dissonance , the subject is easy to hear.

In this excerpt, the subject is presented in a new key surrounded by increased dissonance and chromaticism : This time, the added voices “block” or “interfere” with the familiar subject, rendering it harder to follow.

At the opening of the Finale of Frederic Chopin’s Sonata No. 2 in b-flat minor , dissonance and chromaticism is so pervasive that the tonality is not discernible. Only at the end of this excerpt is there a “glimmer “of diatonicism .

Thus, the primary functions of dissonance are to direct the music forward, highlight the independence between musical lines, heighten the expressivity and make the music more perceptually challenging.

By adding ambiguity and tension , postponed closure , chromaticism and dissonance can help shake the foundations of a key. If the cadences still remain within the key, the music has not moved yet. However, if the cadences begin to roam, the music has embarked on a harmonic voyage. We will now study what happens when music leaves a key.