Chords Part 2: Dominant Seventh Chords
In part one of this series we discussed major and minor triads. In todays posting, we will look at Dominant Seventh chords. These chords are much like major triads, except they have one additional note not found in your basic major chord or triad. In order to understand dominant seventh chords and their various roles fully, there are a few things to keep in mind.
Construction of Dominant Seventh Chords
At first, it is simplest to think of dominant seventh chords as coming from major triads. What does that mean? It’s actually pretty simple: to construct a dominant seventh chord you simply take a major triad and add a minor seventh on top of the 5th. Let’s look at a C dominant seventh chord (side note: we notate these chords by writing the name of the major chord followed by the number 7—so in this case, we’re looking at C7).
We first take a C major triad. As discussed in part one of this series, this consists of C as the root, E as the major third, and G as the fifth. From there, we simply add one more note, the interval of a minor seventh.
The minor seventh is the interval that is one whole step below the octave of the root. If our root is C, our octave will also be C; one whole step down is B-flat (Bb). As a result, the notes found in a C7 chord are C-E-G-Bb.
Wait a minute. Am I really saying that we combine a major triad with a note most commonly found in a minor scale to make a dominant seventh chord? It may seem so, but that’s not quite right. In order to make sense of this chord, we have to place it in its proper context, which is as the chord based off of the 5th scale degree in a major key. Time for an example:
Let’s say we are in the key of F-major. The notes in an F-major scale are F-G-A-Bb-C-D-E-F. If we then do a little thing called major scale harmonization (this will be discussed in more detail in another post), we can construct chords with roots on each of the notes present in the above scale.
As I previously mentioned, the dominant seventh chord will appear when a chord is constructed with the 5th scale degree as its root, so in this case that root will be C (F is 1, G is 2, and so on until we reach C in the 5th spot). If we start on C (in other words if we briefly pretend that C is our root, not F) and then take the 3rd, 5th and 7th notes after it, we should have a C dominant seventh chord, or C7.
Put more simply, our “new” scale from which we make this C7 chord contains all of the same notes as the F major scale (after all, remember we are still in the key of F major). C is our root, so our scale now looks like C-D-E-F-G-A-Bb-C. We stack the root, third, fifth and seventh notes, C-E-G-Bb, and there you have it, a C major triad with a minor seventh on top, or a C7 chord.
Application of Dominant Seventh Chords
In music, the term dominant is very important. It refers to the harmonic quality that leads to a return to the tonic, meaning the root chord in a given key (in this case, it means the chord that will bring us naturally back to our F major chord). This might be tough to grasp, so let your ears confirm this concept.
Try playing the following chord progression: F—Bb—C7—F. Upon arriving at the final F major chord, it should sound like you have reached a point of finality. In other words, once you reach the final F major chord, it should feel like you have found a logical stopping point. This is the most fundamental quality of the dominant seventh chord—bringing you to a point of closure in a song or chord progression.
Of course, this is not the only application of dominant seventh chords. In contemporary music they pop up everywhere—perhaps most notably in the blues. When playing a I-IV-V chord progression where each chord is a dominant seventh chord, (for example F7-Bb7-C7) the result is a funky, bluesy sounding progression. Try it for yourself.
There are many more applications of the dominant seventh chord, easily enough to write a book on the subject, so I will leave you with this idea: try replacing major chords with dominant seventh chords from time to time and chances are, you’ll come up with some pretty neat sounding chord progressions. That’s all for now. Stay tuned for the next post in this series covering major and minor seventh chords.