A seventh chord is one of the most frequently-used extensions of a triad, adding depth, emotion and complexity to music.
Seventh chords play an essential part in piano music of all genres and this article will explore their various types and qualities.
Definition
Seventh chords are constructed using three-note triads with an extra pitch that resonates a seventh above their root chord, adding dissonance for depth and character that can be heard in songs like Coldplay’s “A Sky Full of Stars”.
As with triads, seventh chords can be identified by their quality and inversion. We’ll discuss inversions more thoroughly in the Inversions and Figured Bass chapter; but for now let’s consider an example voicing of a seventh chord with closed spacing.
As illustrated by the following diagram, seventh chords can be divided into two distinct categories: diminished and major. Minor seventh chords consist of a minor third, a diminished fifth, and a diminished seventh above their root; on the other hand, major seventh chords utilize a major triad with an ascending dominant seventh above their root.
Origins
There are various seventh chords available to composers; however, equal-temperament tuning systems make use of only major and minor dominant sevenths most often. Other less-common sevenths include those based on augmented or diminished triads but these tend to only appear rarely outside film scores and jazz compositions like Wayne Shorter’s tune Iris.
To create a 7th chord, begin by starting from the root of a triad you wish to construct and adding any note that forms a seventh above it. These intervals are typically named according to what kind of triad and seventh they form – hence G7 or C7 respectively – though sometimes shorter nomenclature like maj-7 or min-7 is used instead.
Consonance
Addition of a seventh interval transforms a triad into an extended chord, often featuring more dissonant notes than consonant ones and necessitating stricter resolution.
Example: A dominant 7th chord with a flat seventh should resolve down by one step to its sonorous third due to the flat seventh’s ability to disrupt stability within its tonic triad and create dissonant gaps in it.
However, this does not always hold true; some extended chords contain consonant seventh or even perfect fifth tones that do not need to be resolved strictly.
Dissonance
As with triads, seventh chords are classified based on their root, quality, and inversion. A dominant seventh chord typically features a major key signature while its top can either be minor or major in nature.
Major and minor dominant seventh chords are two of the most frequently employed seventh chords because they’re straightforward to play and create lots of tension within music.
Minor diminished chords may not be common, but they can add a jazzy sound to a piece. They are formed by taking a minor triad and adding a diminished seventh nine semitones above its root; an example can be heard at the start of Latin jazz song “Sway”.
Resolution
Seventh chords add emotions and colors to regular major or minor triads by adding a seventh interval, creating tension or beauty through their dissonant qualities. There are five types of seventh chords commonly found in Western music: major, minor, diminished, augmented and half-diminished; although minor major and augmented seventh chords exist but less frequently (though still found elsewhere).
As with triads, seventh chords can be identified by their root, quality, and inversion. As inversion occurs naturally with seventh chords, their resolution usually involves falling-fifth root motion; meaning that when they resolve they move down one step until reaching sonorities with roots one fifth lower – such as Louise Farrenc’s opera La Straniera where Louise Farrenc employed an ii6/5 chord as an example.