Seventh chords can add emotion, tension and complexity to any composition. They feature four notes – the root note, third, fifth and seventh above it.
The initial three notes form a diminished triad and its seventh note is played half-diminished below its octave for an exciting sound.
Major
Major seventh chords consist of three consecutive triads with an extra note that resonates a seventh up from their root note, creating dissonant notes within the chord itself and adding dissonance; as with all seventh chords, these must be treated carefully.
The Maj7 chord can be found across a range of musical genres and adds an elegant, soothing quality to a song’s progression. Common examples include jazz, bossa nova and ballads where this chord’s presence adds sophistication.
Chords built with scale degrees 1 and 2 do not typically include sevenths as this would compromise the stability of their tonic triad. Still, tonal music frequently uses these chords due to their natural harmonic properties.
Minor
Seventh chords expand upon the interval qualities of triads by adding an additional pitch which sounds one seventh above their root note. As such, their sound can be dissonant, and requires careful voice leading in order to avoid tension or unpleasantness in performance.
Minor seventh chords, like their major and minor counterparts, consist of three elements – root, minor third and perfect fifth – with minor sevenths differing by having their root a half step lower than it would in major triads.
To identify the quality of a seventh chord, just look at its key signature for its root triad and compare it with interval qualities in other intervals in that particular seventh chord. Most textbooks label these chords by their type (triad type and seventh type). Roman numeral notation indicates this with terms like “i7” for scale degree 1 triads and “ii7” referring to two other types (for instance i7 for 1st degree triads and “ii7” referring to scale degree 2 built triads). Therefore a seventh chord that contains both major and minor parts is sometimes simply called “major/minor 7th chord”.
Dominant
The dominant seventh chord features a leading tone which the human ear wants to resolve into the tonic; this makes it one of the strongest functions of this type of chord and is why it is often called the V-I resolution chord.
Musicians frequently turn to dominant seventh chords because they add tension that major and minor chords alone can’t create. A great example is Jimi Hendrix’s iconic guitar solo “Purple Haze”, where Jimi used his dominant seventh to add attitude and tension into the piece.
Hank Williams’ country classic “Hey Good Lookin'” uses a C dominant seventh chord as its foundation to give it that classic country feel. Dominant seventh chords can also be extended further with flat-9’s, sharp-9’s or even flat-13’s for jazz musicians to add extra dimension – or reduced into half-diminished sevenths which create tension but have more of a minor feel to them.
Half-Diminished
The half-diminished (also referred to as an m7b5) chord can be an invaluable way of creating smooth tension relief. This chord contains three of its four notes in common with a minor 7th chord; however, unlike fully diminished chords its seventh is only diminished once. Spelling of this chord should read as 1b3,b5,bb7 for easy reference in terms of scale intervals.
Diminished chords can be used as passing chords in progressions, to add variety to standard progressions, and create tension that needs to be resolved by chords with greater ties to your song’s key. They are commonly found on minor mode II chords and often lead to dominant V chords; you could also try using modal mixture to get this same effect using major mode; the result can create some pretty cool sounds!