Added tone chord
An added tone chord, or added note chord, is a non-tertian chord composed of a triad and an extra "added" note. Any tone that is not a seventh factor is commonly categorized as an added tone. It can be outside the tertian sequence of ascending thirds from the root, such as the added sixth or fourth, or it can be in a chord that doesn't consist of a continuous stack of thirds, such as the added thirteenth (six thirds from the root, but the chord doesn't have the previous tertian notes – the seventh, ninth or eleventh). The concept of added tones is convenient in that all notes may be related to familiar chords.
Inversions of added tone chords where the added tone is the bass note are usually simply notated as slash chords instead of added-tone chords. For example, instead of Cadd2/D, just C/D is used.
An added tone such as fourth voiced below the root may suggest polytonality. The practice of adding tones may have led to superimposing chords and tonalities, though added tone chords have most often been used as more intense substitutes for traditional chords. For instance a minor chord that includes a major second factor holds a great deal more dramatic tension due to the very close interval between the major second and minor third. Igor Stravinsky's polytonal Symphony of Psalms contains many added tone chords.