Seventh chords, similar to triads, are built using intervals in the scale. However, unlike their triadic counterparts, seventh chords do not always fall under one of three categories according to their intervallic content.
For an easier approach, think of seventh chords as triads with one extra note added on top. This will make understanding their qualities much simpler.
Major
Since seventh chords appear so frequently in tonal music, to save space on music notation pages it’s often more efficient for their symbols to omit information such as whether or not the chord is major or minor.
A seventh chord built around C will typically feature a B-flat instead of C-natural as the latter would harmonize with tonic harmony and create dissonance. On the contrary, major sevenths form harmonic fifths with their tonic trios, making them less vulnerable.
Cmaj7 chord is an extremely common tonic seventh chord used as the foundational chord in classical compositions. Dominant seventh chords can also be written with just their tonic note followed by 7. This gives you all of the information that you need in order to play the chord correctly.
Minor
Music notation often omits details about chord quality, such as whether a seventh chord is major or minor, to save space on the page and rely on musicians to identify these characteristics based on their context in key signature of root note.
To identify a minor seventh chord, musicians use an uppercase M followed by a lowercase 7 (m). An optional bass note may also be added.
Roman numeral labels for seventh chords depend on their quality: uppercase for major, minor and diminished triads and lowercase for minor/diminished triads. A “-o” may be added after lower-case Roman numerals to indicate fully diminished seventh chords or half-diminished seventh chords used commonly in jazz music.
Dominant
Dominant seventh chords are built by adding a 4th note that is a minor 7th interval above the root note of the chord, typically used in jazz music and particularly modal jazz contexts.
Voiced without using a third note as this creates a tritone interval and may sound dissonant, they typically contain suspended 4ths (G7sus4) instead to avoid this problem.
Dominant 7th chords can add tension and urgency to a progression by including a leading note that can guide listeners toward resolution of the tonic chord. They’re frequently found near the end of pieces of music; these chords can even be found in blues and pop music!
Half-diminished
A half-diminished chord is composed of diatonic II chord in minor mode and usually resolves into dominant V chord, often ending on its root note (usually Bm7b5 or Dim7). It’s often used as the vii chord for major modes; although its exact voicing may differ (eg Bm7b5 or Dim7).
Building a half diminished chord above any note requires following an established pattern of intervals. You can locate this using the Triad Chord Quality Table and searching for notes between root and desired note that make up that interval.
The chord can be played in various ways and makes an effective passing chord, whether solo or combined with other chords. Its presence offers contrast against major and minor chord progressions while creating drama and tension within your progressions.
Flatted
Seventh chords represent an intermediate step beyond triads in terms of complexity, and their recognition can open up new genres for musicians. A seventh chord consists of an underlying triad plus an additional note – usually either major (M7), minor (m7) or diminished (7th) is present above the root note. These types are commonly found.
As with triads, seventh chords can be written out on music staffs with names and symbols to identify them. Chord extensions are frequently notated using “sus” notation; for instance Csus2 or C7sus may be noted. Furthermore, their parenthetical notation can indicate either Cmaj or Cm.