21: A Basic Introduction to the Types of Seventh Chords

Seventh chords are of vital harmonic importance.  Any triad can easily become a seventh chord, simply by continuing along the pattern of adding thirds. The seventh built on scale degree 1 uses 1-3-5 from the triad, plus 7; the seventh built on scale degree 2 uses 2-4-6-1; and so on. What kind of sevenths those are depends on 1) the scale from which those scale degrees were created and 2) any extra alterations done to the underlying triad or the newly added seventh.

One seventh in particular, that built as an extension of the triad on scale degree 5, is, as I see it, unquestionably the second-most important chord in the whole harmonic language, bested in importance only by the tonic chord.

Anywhere where there is a triad, in general, there can be a seventh substituted in its place. Especially if the triad is the dominant chord, and so the seventh is the one built on the fifth scale degree is the point of maximum harmonic tension, especially if it cadences immediately thereafter to the tonic.

There are a few types of sevenths, named after how they are constructed. So you can see the relationships more clearly, I’ll build everything rooted at C:

1. The major seventh: build a major triad and then stack a fourth note, which is a major seventh above the root of the chord. C E G B.

2. The minor seventh: build a minor triad and then stack a fourth note, which is a minor seventh above the root of the chord. C Eb G Bb

3. The fully-diminished seventh: build a diminished triad and then stack a fourth note, which is a diminished seventh above the root of the chord: C Eb Gb Bbb

4. The half-diminished seventh: build a diminished triad and then stack a fourth note, which is a minor seventh above the root of the chord: C Eb Gb Bb

5. The augmented seventh: build an augmented triad and then stack a fourth note, which is a minor seventh above the root: C E G# Bb

6. The minor-major seventh: build a minor triad and then stack a fourth note, which is a major seventh above the root of the chord: C Eb G B

7. The major-minor seventh (also called the dominant seventh): build a major triad and then stack a fourth note, which is a minor seventh above the root of the chord: C E G Bb

That last chord, the major-minor seventh (hereafter always referred to as the “dominant seventh”), is the all-important chord mentioned before the list began. In fact, if someone says to you, for example, “Play a G7” with no further elaboration on what kind of seventh from that list they want you to build, you can, with about 99.9% confidence, build and play G B D F.

I mentioned in our discussion of modes a few articles ago how important mixolydian would come to be. This was why: because if you build a seventh on the root of Mixolydian (and therefore the dominant of major/Ionian), you end up with a major triad plus a minor seventh—exactly what a dominant seventh is. Since the dominant seventh chord is so key to our harmonic language, understanding the pattern behind building mixolydian becomes incredibly important.

Comments

Post a Comment

Popular posts from this blog

35: Figured Bass

Image
  There’s a system of notating harmonies that’s rather unique to the Baroque era, but which is so frequently used there, and so important to it, that no discussion of theory would ever be complete if we did not cover it. This is the notation of figured bass: “figured,” in the sense of using figures (numbers) to notate the bass. Figured bass was, in a sense, its own notation completely separate from the five lines and four spaces of the staff, which was nearly exclusively the purview of cellists, bassists, harpsichords, and organists.  Figured bass, fair warning, can be intimidating at first. But, just as with anything else we’ve covered so far, the more you practice reading it, the better you’ll get.  In this system, we use numbers to indicate intervals above the bass. We stack them, and this is how we build chords. If you can’t stack them, nowadays, it’s perfectly fine to use slashes and write the numbers horizontally.  Let’s start with the easiest figured bass nota...
Read more

58: Swell pedals and swell shades

There’s one pedal that we haven’t discussed on the organ because it isn’t one of the “note” pedals—in fact, it’s the only one that doesn’t have a pitch. Instead, the missing pedal is the swell pedal. Look at the body of the organ (the assembly of where all the pipes are, as opposed to the “console”, where the organist sits and plays the instrument—these may or may not be physically close to each other), and you’ll probably see what kind of look like plantation shutters. (If you know where my parish is, then this feature of the organ is very clearly visible on ours. Your local organ might not be so obvious.) These shutters, called “swell shutters/shades,” show or hide the pipes of the organ. Organs have instantaneous dynamic control—the amount of pressure you put on a key dictates how much air flows through the pipes, just like a piano allows you to adjust dynamics on the fly by changing the amount of pressure with which the hammer hits the string(s) given the pressure on the key. Thes...
Read more

54: Trills in the Baroque vs. Classical Periods

Image
Baroque music is known for its incredibly technical and ornamented style. The most common and fundamental of those ornaments is our focus today: the trill. Most simply, a trill is a very fast, repeated alternation of two notes. In the vast majority of cases, those notes are adjacent, but that is not a requirement. Given how fast and common they are, regardless of what you play—whether it’s a string, wind, or keyboard instrument, or your voice—they have a reputation for being quite tiring to play. The period matters when considering a trill. Classical and later composers treat trills, in a sense, in the opposite manner than Baroque composers do. Let me show you two examples: First, the Baroque way of thinking. This is a PAC:   and especially in the Baroque era, when the plucked harpsichord dominated over the hammered piano, it was hard to sustain sounds for long since the sound of the plucking decays quickly. The trill was developed in response, out of a need both to ornam...
Read more