Understanding harmonies makes it possible to gain a greater appreciation for all types of music. Harmonies create context and a foundation for melodies by providing additional movement and color to support the melodic ideas. Several ways to create harmony exist, and each kind of harmony has its own purpose within music. Learning about the kinds of harmonies will make it possible for you to identify harmony in context.
One of the most basic types of harmonies involves two independent lines sounding at the same. Also known as counterpoint, this type of harmony makes it possible to create harmony by juxtaposing two melodies. As an example, Gregorian chant often consists of simple, two-note harmonies. This type of harmonization must be used cautiously to avoid parallel motion between the lines. When both lines move at the same interval, it gives the impression that both lines are actually just one line. To prevent this, composers will make each line move in an opposite direction (oblique motion) or contrary to each other (contrary motion.)
Triads can be any series of three notes played simultaneously; however, it is most common for triads to consist of a bass note called the root, an interval of a third above that and a fifth above the root. Triads create harmony when they are performed and create chord progressions when they are linked in a logical way. For instance, when a series of chords changes from one triad to another, if at least one note stays the same, the piece is considered to be a chord progression. If the triads move randomly without a logical pattern, they are considered to be chord successions. The basic types of triads are major, minor, augmented and diminished.
Seventh chords are triads that consist of a root, third and fifth and that have a seventh added to the top of the chord. These chords typically help create resolutions in harmonies since the seventh typically "wants" to resolve. This resolution creates a strong pull between chords and helps to create a sense of finality in a composition. Seventh chords include major-minor sevenths, major sevenths, fully diminished sevenths, half-diminished sevenths and minor sevenths. The type of seventh chord is determined based on the triad quality and the interval of the seventh in relationship to the bass.
In addition to traditional harmonies, there are also several extended harmonies. Harmonies created by stacking fourths such as in much of Aaron Copland's music, or harmonies created by fifths are commonly found in modern music. Tone clusters also exist in which several notes that may not have a relationship to each other are pieced together. Additional methods include using uncommon scales such as the whole-tone scale and octatonic scale for the basis of chords are commonly found in modern music.