Understanding Dissonant and Consonant Chords

Consonant chords sound harmonious and pleasing to western ears, while dissonant chords sound clashing and elicit a feeling of tension. The amount of consonance or dissonance in a chord has been proven to affect a person's mood, and there are some studies that show that even amusic people recognize dissonant chords as "sad" and consonant ones as "happy" sounding. No explicit music knowledge is needed to recognize the difference; the degree of dissonance in a piece of music has been shown to create biochemical effects in the listener associated with different pleasant and unpleasant emotional states.

History and Modern Studies

The effect of consonant and dissonant chords on the listener has been recognized in western music at least since the Greek mathematician Pythagoras in the 5th century BCE. Recent psychological research has shown that even 4-month-old infants prefer consonant to dissonant music. However, scholars are undecided as to whether the recognition is a learned or inherent trait, because studies on people from non-western cultures have varied results, and studies on non-human species such as chimpanzees and chicks are inconclusive as well.

Musical chords are made up of two or more tones sounding together, and consonance/dissonance is the result of the comparison of the sound frequencies of the notes played. That was first recognized by the 19th-century German scientist and philosopher Herman von Helmholtz. Consonant, pleasing-sounding combinations of musical tones are those with simple frequency ratios, such as the octave, in which the frequency of the lower tone is half the frequency of the higher tone (1:2); the perfect fifth with a ratio of 2:3; and the perfect fourth at 3:4. Very dissonant intervals such as the minor second (15:16) or the augmented fourth (32:45) have much more complex frequency ratios. In particular, the augmented fourth, called the tritone, is what the Middle Ages knew as the "devil in music."

Dissonant and Consonant Chords

In Western music the following intervals are considered consonant:

• Minor third—For example from C to Eb
• Major third—For example from C to E
• Perfect fourth—For example from C to F
• Perfect fifth—For example from C to G
• Minor sixth—For example from C to Ab
• Major sixth—For example from C to A
• Octave—For example from C to C

On the other hand, these intervals are considered dissonant:

• Minor second—For example from C to Db
• Major second—For example from C to D
• Minor seventh—For example from C to Bb
• Major seventh—For example from C to B
• Tritone—For example from C to F#; also known as the augmented fourth or diminished fifth, the tritone has an interval of 3 whole steps

Most often dissonance is resolved by moving to a consonant chord. This makes the initial feeling of tension created by dissonant chords to reach a resolution. The common term for this is tension and release. However, dissonance doesn't always need to be resolved, and the perception of chords as dissonant tends to be subjective.

Sources:

• Cook ND. 2009. Harmony Perception: Harmoniousness is More Than the Sum of Interval Consonance. Music Perception: An Interdisciplinary Journal 27(1):25-42.
• Cousineau M, McDermott JH, and Peretz I. 2012. The basis of musical consonance as revealed by congenital amusia. Proceedings of the National Academy of Sciences of the United States of America 109(48):19858-19863.
• Schön D, Regnault P, Ystad S, and Besson M. 2005. Sensory Consonance: An ERP Study. Music Perception: An Interdisciplinary Journal 23(2):105-118.
• Sollberger B, Rebe R, and Eckstein D. 2003. Musical Chords as Affective Priming Context in a Word-Evaluation Task. Music Perception: An Interdisciplinary Journal 20(3):263-282.