Root (chord)

Root, in red, of a C major chord (Playⓘ). The root is doubled at the octave.
Root notes (blue) and bass notes (red, both=purple) from an 18th-century Chorale Playⓘ

In the music theory of harmony, the root is a specific note that names and typifies a given chord. Chords are often spoken about in terms of their root, their quality, and their extensions. When a chord is named without reference to quality, it is assumed to be major—for example, a "C chord" refers to a C major triad, containing the notes C, E, and G. In a given harmonic context, the root of a chord need not be in the bass position, as chords may be inverted while retaining the same name, and therefore the same root.

In tertian harmonic theory, wherein chords can be considered stacks of third intervals (e.g. in common practice tonality), the root of a chord is the note on which the subsequent thirds are stacked. For instance, the root of a triad such as E Minor is E, independently of the vertical order in which the three notes (E, G and B) are presented. A triad can be in three possible positions, a "root position" with the root in the bass (i.e., with the root as the lowest note, thus E, G, B or E, B, G from lowest to highest notes), a first inversion, e.g. G, B, E or G, E, B (i.e., with the note which is a third interval above the root, G, as the lowest note) and a second inversion, e.g. B, E, G or B, G, E, in which the note that is a fifth interval above the root (B) is the lowest note.

Regardless of whether a chord is in root position or in an inversion, the root remains the same in all three cases. Four-note seventh chords have four possible positions. That is, the chord can be played with the root as the bass note, the note a third above the root as the bass note (first inversion), the note a fifth above the root as the bass note (second inversion), or the note a seventh above the root as the bass note (third inversion). Five-note ninth chords know five positions, six-note eleventh chords know six positions, etc., but the root position always is that of the stack of thirds, and the root is the lowest note of this stack (see also Factor (chord)).

Root position, first inversion, and second inversion C major chords Play root position C major chordⓘ, Play first inversion C major chordⓘ, or Play second inversion C major chordⓘ. Chord roots (all the same) in red.
Root position, first inversion, and second inversion chords over C bass Play root position C major chordⓘ, Play first inversion A minor chordⓘ, or Play second inversion F major chordⓘ. Chord roots in red.