Seventh chords are one of the most frequently encountered extensions of triads, and there are five primary varieties with their own distinctive sounds.
To identify a seventh chord, it is necessary to understand its root note as well as the quality of its triads and sevenths. Chords are typically written out with their root note indicated and key signature written next to it (in case any accidentals appear – see Inversion and Figured Bass chapter for more on this topic), as well as an additional symbol indicating its position within music.
Triads
If you want to add variety and depth to your harmonic palette, seventh chords are an excellent way to do just that. They represent an extension of basic triads you learn and offer an array of unique sounds you can work with.
As with triads, seventh chords can be identified based on their root, quality, and inversion. We will explore this process in more depth in our Inversion and Figured Bass chapter; for now let’s use an example where the lowest note forms part of a major triad chord as an illustration.
The quality of a triad is determined by its building block; in this instance, C major is chosen. Because a sharp seventh would sound harsh in C# key, its sound has been softened slightly so as to achieve diminished or minor seventh qualities (C#o). This characteristic sound typifies minor seventh chords.
Major
Seventh chords add one additional note above the triad, creating four-note chords. Western music typically employs five major types of seventh chord (tertian) commonly: major, minor, dominant, half-diminished and diminished chords.
Many seventh chords are labeled using the Roman numeral system, such as major and minor thirds; thus they will feature open noteheads next to their letters (ie: I7 = major chord and II7 = minor chord). But there can also be exceptions;
Seventh chords can be daunting to the uninitiated, but once you understand their purpose in music they become much less complex and intimidating. Try this easy progression on an acoustic guitar to practice chord shapes and fingerpicking technique – plus use this as an excuse for an awesome thumb workout! – i7 maj7 ii7 bmin7.
Minor
Seventh chords can add a whole new depth and dimension to your playing, opening up many genres of music for you. They’re easy to create too – just think of an underlying triad and then add one extra chord on top – no complicated formula needed here!
Seventh chords offer more rich harmonic textures than their triad counterparts due to the presence of dissonant sevenths, thus necessitating more complex voice-leading rules than those for triads.
There are five basic seventh chord qualities used in tonal music: minor seven, major-minor seventh, half diminished seventh and fully diminished seven chord qualities. Let’s start with minor sevenths: these can be created from taking a diminished triad and adding one half step below its octave as in this example.
Diminished
A diminished seventh chord can act like four chords in one and is an ideal way to connect chord progressions that usually wouldn’t work together.
Like any seventh chord, the diminished is composed of two equally spaced tritones that can be resolved using contrary motion – such as expanding fourths out to sixths or contracting diminished fifths down to thirds.
To form a diminished seventh chord, simply lower the two lowest notes by half steps and play them as normal – this process of spelling seventh chords is similar to how we use them for triads; they share similar chord qualities too! Here’s how it’s done:
Inverted
Inversions can be an excellent way to practice the intervals that comprise a seventh chord. Start by playing a root position seventh chord with your left hand, identifying each interval individually with your right. When this becomes easy for you, switch gears and move onto practicing first inversions followed by second inversions.
An inversion of a seventh chord determines its resolution. For instance, a V7 chord in second inversion (7) typically resolves down by way of a falling fifth; on the other hand, 6/7 in second inversion (6/5) doesn’t resolve this way.
Just like triads, seventh chords can be inherently dissonant and should be handled carefully; however, their unique sound lends itself to various musical purposes that will be discussed further in Chapter 19. In the meantime, let us look at a couple of common seventh chord progressions.