A seventh chord is a type of chord used in music theory that is created by adding a note of a seventh above the root of a chord. It is made up of four notes and consists of a triad (three notes) and a note that is a seventh interval above the root note of the chord.
The most common type of seventh chord is a dominant seventh chord, which is made up of a major triad (consisting of a root note, a major third, and a perfect fifth) and a minor seventh interval above the root note.
However, it is possible to add different types of sevenths to different types of triads, resulting in many different types of seventh chords.
Originally, the seventh was introduced as a nonchord tone used to embellish the chord and create movement in a specific direction. Over time, the seventh became a more integral part of the chord itself, especially in modern music genres like jazz.
As the Western ear became more accustomed to dissonance, the acceptance of equal temperament during the 19th century also reduced the dissonance of some earlier forms of seventh.
Seventh chords and their inversions are often indicated using additional numbers alongside Roman numerals. These chords can be found in root position or any one of the three inversions. Below, you will find a breakdown of each inversion and its corresponding notation:
- Root Position – A “7” after the Roman numeral denotes a seventh chord in root position. This means that the notes a third, a fifth, and a seventh are located above the bass note.
- First Inversion (Third in the Bass) – A “6” and a “5” following the Roman numeral indicates a seventh chord in the first inversion. In this case, the notes a sixth, a fifth, and a third are located above the bass note.
- Second Inversion (Fifth in the Bass) – A “4” and a “3” after the Roman numeral represents a seventh chord in the second inversion. The notes a third, a fourth, and a sixth are located above the bass note in this inversion.
- Third Inversion (Seventh in the Bass) – A “4” and a “2” following the Roman numeral indicates a seventh chord in the third inversion. In this case, the notes a fourth, a second, and a sixth are located above the bass note.
The numbers after the Roman numerals represent intervals found above the bass note, and the notes can be played in any octave above the bass note.
Here are some examples of compositions that use seventh chords and Roman numerals to indicate their inversions:
- “Ständchen” by Schubert – In this piece, the supertonic chord (iio) occurs twice: once in the first inversion (65) and once in the second inversion (43). The “o” with a slash through it signifies a half-diminished seventh chord.
- “Go Down Moses” – This example employs the supertonic seventh chord in third inversion (42) and the dominant seventh chord in second inversion (43).
- Piano Sonata, Op. 2, No. 1 by Beethoven – This piece also features the use of seventh chords and their inversions.
- Song without Words, Op. 38, No. 4 by Mendelssohn – Another example of a composition using seventh chords and Roman numeral notation.
Understanding how seventh chords and their inversions are represented using Roman numerals and additional numbers can provide valuable insight into harmonic analysis and composition.
If we take the C major triad, which consists of the notes C, E, and G, and add a seventh interval above the root note (C), we get a C dominant seventh chord. The seventh interval above C is B-flat, so the C dominant seventh chord is made up of the notes C, E, G, and B-flat.
Another example could be the A minor seventh chord, which consists of the A minor triad (A, C, and E) and the seventh interval above the root note (A), which is G. So the A minor seventh chord is made up of the notes A, C, E, and G.