A seventh chord is defined as a chord composed of a triad, plus a fourth note that forms the interval of a seventh (diminished, minor, or major) above the root of the chord.
In the classical music theory classroom, students are usually called upon to be able to notate and identify five types of seventh chords:
The fully diminished seventh chord (solfege: ti re fa le), a chord composed of stacked minor thirds that functions most commonly as chord viio7 in minor keys.
The half-diminished seventh chord (solfege: ti re fa la or re fa le do), a chord composed of a diminished triad stacked under a major third, that functions most commonly as chord viiø7 in major keys or chord iiø7 in minor keys.
The minor-minor seventh chord (solfege: re fa la do or la do mi sol), a chord composed of a minor triad stacked under a minor third, that functions most commonly as chord ii7 or chord vi7 in major keys.
The major-minor seventh chord (solfege: sol ti re fa), a chord composed of a major triad stacked under a minor third, that functions as chord V7 in both major and minor keys.
The major-major seventh chord (solfege: do mi sol ti), a chord composed of a major triad stacked under a major third, relatively uncommon in classical music but still common enough to make it a good idea to study and recognize.
In one of the appendices to Cello Practice, Cello Performance, I wrote an exercise in arpeggios in which I supplied fingerings for these five types of seventh chords, beginning each one on D for the sake of intervallic comparison.
My views on how best to learn these chords continue to evolve, and these days I think it’s even more helpful to learn about seventh chords using their harmonic function as a context. Chords don’t exist in a vacuum — they are always part of something bigger than themselves — so I composed some (I hope) fun melodies that do just that.
In them, I placed the seventh chords in the kind of context that you might find them in when you come across them in repertoire. For example, I place the fully diminished seventh chord in D minor, beginning on ti in D minor (C-sharp) and resolving it, just as the fully diminished chord resolves in diatonic harmony.
Some of the seventh chords have more than one common function in diatonic music, such as the minor-minor seventh chord. I put a little musical “in-joke” into my exercise here — a quote from Debussy’s Girl With the Flaxen Hair that is one of the most famous melodic uses of this type of chord.
Click here to download a free, high-resolution PDF of the whole etude.