Introduction to Harmony
We have already learned that melody refers to pitches played in sequence. Harmony, on the other hand, deals with pitches sounded simultaneously. To put it another way, melody is the horizontal aspect of pitch, and harmony is the vertical aspect.
Harmonies can be used to add support and depth to a melody, or sometimes harmony is simply the result of many melodies overlapping each other (as in polyphony). Harmony is also important for the form (large-scale organization) of musical works and can be used to give long pieces a sense of unity and structure.
Consonance and Dissonance
Some harmonies sound pleasing and stable, while others clash and seem unstable. The stable harmonies are called consonant, while the unstable harmonies are called dissonant. Consonant harmonies give a sense of serenity and rest to a piece, while dissonant harmonies create tension and anxiety. Each style of music has its own conventions about how consonance and dissonance are managed and therefore which harmonies are preferred.
The perfect intervals (unison, octave, perfect 4th, and perfect 5th) are considered the most consonant intervals. The most dissonant intervals are a half step away from the perfect intervals: minor 2nd, major 7th, and tritone (also called augmented 4th or diminished 5th). The other intervals fall somewhere in between, with the major 2nd and the minor 7th being somewhat dissonant, and the major and minor 3rds and 6ths being somewhat consonant.
|minor 2nd, half step|
|Major 2nd, whole step|
|tritone (augmented 4th, diminished 5th)|
Dissonant harmonies can make listeners feel unsettled and tense. This tension makes listeners wish for the release and resolution of consonant harmonies. When dissonant harmonies change to consonant ones, it is called resolution. Longing for resolution can give music a sense of forward momentum, and the way that resolutions are granted or withheld can make listeners feel either satisfied or frustrated. Just as some stories are left unresolved, so are some harmonies. For more about harmonic resolution, see Cadences.