Here, you will explore all the different seventh chords that are available to you. You should begin to think like this: A seventh chord is nothing more than a triad with an added seventh interval (when measured from the root). Doing so will give you at least eight seventh chords (four possible triads and two sev-enths), although there is one more that breaks the rules a touch (more on that soon). Go through them one by one so you can see how they are put together and how they are named.

Major Triads with Sevenths

If you take a major triad and make it into a seventh chord, you can come up with only two possibilities: a major triad with a major seventh on top, and a major triad with a minor seventh on top.

Start with FIGURE 9.3.

When you look at that chord, you can look at two things: first, you have your major triad, D (D–F#–A), and you have an added C#. The interval from the root of the chord to the seventh (D to C#) is a major seventh. Call this chord a major/major seventh chord for a second because it tells you exactly what you have:a major triad with a major seventh interval added. Now, the rest of the world will simply call this chord a major seventh, as in D major seventh, or Dmaj7 for short. Many theorists will use “major/major seventh” to be more specific, but if you say “D major seventh,” you're saying exactly the same thing. The major seventh chord is found on the first (tonic) and fourth (subdominant) degrees of a harmonized major scale.

You could think of the formula for a major seventh chord as being:1, 3, 5, 7 (This is if you take the scale degrees from a major scale.)

Extra Credit

The major seventh chord is interesting for two reasons: First, you can spell it simply by choosing the first, third, fifth, and seventh notes from any major scale. This is because a major seventh chord is the tonic seventh chord in a major key. It's also interesting that its proper name of “major/major seventh” shortens to simply “major seventh.”

The next possible seventh chord would be FIGURE 9.4.

Looking at this chord, you see another D major triad (D–F#–A) and an added seventh of C. The interval between D and C is a minor seventh. This chord is fully called a major/minor seventh chord. When it's shortened, it's simply called a seventh chord, as in G7, or D7 in this case. Since the term seventh chord is far too general for music theory, theorists and many musicians call this chord a dominant seventh chord because, as illustrated in FIGURE 9.1, this chord occurs only on the fifth scale degree, which has the proper name of the dominant scale degree. Whichever you call it, G7 or G dominant seventh, both are acceptable and correct.

The formula for a dominant seventh chord is: 1, 3, 5, 7 (if you take the scale degrees from the major scale). Dominant seventh chords are really important! It's awfully hard to have harmony without dominant (V) chords.

Minor Triads with Sevenths

When it comes to minor triads with sevenths, there are also two varieties! Start with FIGURE 9.5.

Start with a C minor triad (C–Eb– G) and add the note Bb. The interval from C to Bb is a minor seventh, so this chord is called a C minor/ minor seventh chord. It's shortened to simply C minor seventh or Cm7 or C-7. This is the basic minor seventh chord that is found on the second, third, and sixth scale degrees of a harmonized major scale. Also worth mentioning is that again, just like the major seventh, when both the triad and the seventh are the same (both minor), the name of the chord is simply minor seventh. The minor seventh chord is also the chord you can form by taking the first, third, fifth, and seventh notes from a pure minor scale (Aeolian).

If you wanted to relate the scale to major, its formula would be: 1, b3, 5, b7 (relating the scale degrees to the major scale).

The next seventh chord that you come to is your first “unnatural” seventh chord in that it's not formed in the diatonic major or minor scales. Take a look at FIGURE 9.6.

This C minor triad with an added B natural gives us a very unusual sound — unnatural, even! The interval from C to B is a major seventh, so the full name for this chord would be a C minor/major seventh chord. There actually is no shortening for this chord; it is always referred to as a minor/major seventh chord. The only shorthand you may see is in the chord symbols in popular music: Cm(maj7), C-(maj7) or Cmin(maj7). While these chords have an unusual sound, they can be quite striking and beautiful when used in the proper context. Again, this triad does not occur anywhere in the natural major or minor scales.

Point to Consider

If you were to harmonize the harmonic or melodic minor scales, you would spell a minor/major seventh from the tonic scale degree. This is where modern theorists see the chord coming from. Others think that it is simply the natural extension of trying a minor triad with a major seventh interval added to it. Either way, it exists in jazz and popular music, most famously in “Us and Them” by Pink Floyd, on their legendary Dark Side of the Moon album.

If you were to derive a formula for a minor/major seventh chord, it would appear as follows: 1, b3, 5, 7 (if you take the scales degrees from the major scale).

That's all you can do to minor triads and sevenths! That brings your grand total up to four seventh chords, and you're through only major and minor! Next up: diminished.

Diminished Triads with Sevenths

Diminished chords are a bit tricky, especially when it comes to naming them. Start with the diatonic diminished seventh chord, built from the leading tone of a major scale.

What you have is a B diminished triad with an added A. The interval from B to A is a minor seventh, so the full name for this chord is a dimin-ished/ minor seventh. However, here's where it gets tricky. This chord is called a half diminished chord. Half diminished chords use this symbol:BØ7.

If you wanted to derive a formula for the half diminished seventh chord, it would look like this: 1, b3, b5, b7 (if you take these from the major scale degrees).

This chord, while it may be the “diatonic” chord, is not the typical diminished seventh chord you see. Take a look at another diminished seventh chord, which will explain why that particular chord is called half diminished.

We start with a diminished triad and add an Ab. The interval from B to Ab is a diminished seventh. The full name for this chord would be a diminished/diminished seventh. Just like major and minor seventh chords that share the same name and type of seventh, this is the diminished seventh chord. It's also called a fully diminished seventh chord, but for most people, “diminished seventh” will do. The º symbol for a fully diminished seventh chord is Bº7.

If you wanted to derive a formula for the diminished seventh chord, it would look like this: 1, b3, b5, bb7 (if you take these from major scale degrees).

Note: This is the first time you've seen a double flat in a chord formula! That's because fully diminished seventh chords don't occur in major or minor scales naturally. They are the result of stacking of minor third intervals. You can also derive this chord if you harmonize the harmonic minor scale at the leading tone degree.