Chord
A chord is any combination of three or more different pitches sounding simultaneous. In functional harmony, chords are interrelated through their functions.
Contents
Chord functions in the common practice
The most fundamental of all chord functions is the Tonic, Dominant, and Pre-Dominant.
Tonics
The tonic chord is the name given to a triad whose lowest tone in root position is the first degree of the scale used in any given tonality. In C major, the triad comprised of {C, E, G} is the tonic chord. Likewise, in D minor for example, the tonic would be {D, F, A}. The tonic chord is indicated by the symbol I for major chord or i for the "tonic minor" chord.
Dominant chords
Dominant chords are chords that when employed in common practice harmony will naturally be followed by the tonic.
The dominant chord is the name given to the triad whose lowest tone in root position is the 5th degree of the scale. In C major, the dominant is {G, B, D} when in the root position. In D minor however, the dominant is {A, C#, E}, the A major chord. Whether in a major or minor tonality, the dominant is always a major chord and indicated by the symbol V.
The dominant seventh chord, indicated by the symbol V7, functions just as the normal V chord does, but the construction (in C major: {G, B, D, F}) lends the chord to have a stronger "pull" or sense of resolution to the tonic. This is due to the tendency for the 7th degree of the chord to resolve stepwise and chromatically into the 3rd degree of the tonic chord.
The diminished seventh chord may also vii°7 serve the function of a dominant and often may be treated as such. In C major, the construction is {B, D, F}, essentially a V7 chord in the root position with the root of the chord omitted.
Pre-dominant chords
Pre-dominant chords are chords that when employed in common practice harmony will naturally be followed by the dominant.
The subdominant chord is the triad whose root lies on the 4th degree of the scale. In C major, the subdominant is the F major chord {F, A, C}, however in D minor the subdominant is {G, Bb, D}, or G minor. The subdominant in a major tonality is always a major chord indicated by IV, and in a minor tonality it is always a minor chord, iv.
The supertonic chord is the triad whose root lies on the 2nd dgree of the scale. In C major, the supertonic is the D minor chord {D, F, A}. However in a minor key, such as C minor, the supertonic is always a diminished chord {D, F, Ab}. The supertonic in a major tonality is indicated by ii and in a minor tonality ii°.
A secondary dominant chord or applied dominant is the dominant chord to a chord on any degree other than the tonic of the scale being used. For instance, in C major the vi chord is A minor. A minor itself has a dominant, which is E major. Therefore when the dominant of A minor is used when in the key of C major, the E major chord is a secondary dominant, called V/vi. A popular secondary dominant is the V/V chord, read as "dominant of the dominant." In C major, the dominant is G major, and the dominant of that dominant, or "secondary dominant", is D major.
Figured Bass Notation
