I choose to begin with Major 7ths because of their simplicity. They are not the most common form of 7th chord, but could easily come in second. As with simple chords, it is important that we be able to think in the key of the root of the chord. In order to describe how this chord is built, we will refer to the Triad and the 7th interval. For the Major 7th chord, we use a Major/Major construction. Quite simply, this means a Major triad, and a Major 7th interval above the root.

As an example, let's form a G Major 7th chord.

1. A Major 7th chord is made up of a Major triad, and a Major 7th interval.
2. The name of the chord gives us the root, that is, G.
3. We know that a G Major triad is made up of G, B, and D.
4. The Major 7th Interval above G is F#.
5. Therefore, the notes G, B, D, and F# make up the G Major 7th chord.

G Maj 7th

Let us follow the same procedure again to form a Bb Major 7th chord.

1. A Major 7th chord is made up of a Major triad, and a Major 7th interval.
2. The name of the chord gives us the root, that is, Bb.
3. We know that a Bb Major triad is made up of Bb, D, and F.
4. The Major 7th Interval above Bb is A.
5. Therefore, the notes Bb, D, F, and A make up the Bb Major 7th chord.

Bb Maj 7th

We will now begin to create a new chart for the construction of 7th Chords based on this Triad/Interval method.

Here is the chart as applied to a C chord:

Dominant 7th chords are by far the most common form of 7th chord. In fact, they are so common that, while other 7th chords are written out by several letter and number combinations (such as EM7, F^o7, Db+7, etc.), the Dominant 7th is indicated by just a "7" after the chord name (A7, Gb7, B7, etc.).

There are several reasons as to why it is called a "Dominant" 7th. The easiest to explain is that, when played, it dominates the music in such a way as to make the music resolve to a chord a fifth lower than the Dominant 7th (G Dominant 7th leads to a C). Much like altering simple chords, the Dominant 7th chord can be formed by altering the Major 7th. Instead of using a Major Triad/Major Interval combination, we will use a Major Triad/Minor Interval combination.

The phrase "Major Triad/Minor Interval" may seem odd to you. Don't worry, you're not alone. You won't hear musicians talking about chords like that. Here, though, the phrase is a shorthand way to say, "A 4-note chord built from a Major Triad with an added note the interval of a Minor 7th above the root." In lieu of such a wordy description, I opted to use the term "Major Triad/Minor Interval" when discussing the construction of this particular chord. Elsewhere, we will simply use it's functional name, "Dominant 7th".

As an example, let's form an Eb Dominant 7th chord.

1. A Dominant 7th chord is made up of a Major triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, Eb.
3. We know that an Eb Major triad is made up of Eb, G, and Bb.
4. The Minor 7th Interval above Eb is Db.
5. Therefore, the notes Eb, G, Bb, and Db make up the Eb Dominant 7th chord.

Eb Dom 7th

Let us follow the same procedure again to form a D Dominant 7th chord.

1. A Dominant 7th chord is made up of a Major triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, D.
3. We know that a D Major triad is made up of D, F#, and A.
4. The Minor 7th Interval above D is C.
5. Therefore, the notes D, F#, A, and C make up the D Dominant 7th chord.

D Dom 7th

We will now add to our chart the Major/Minor construction of the Dominant 7th Chord. As you can see, the only difference between the Major 7th and the Dominant 7th is the 7th itself (yes, that is a mouthful!). Since both chords are based on the Major triad, the chart attempts to reflect this similarity by sharing the "Major Triad" box. This will be a helpful feature of the chart, once it is filled in with all six forms of the 7th chord!

Here is the chart as applied to a C chord:

By now, you should be seeing the advantage to using the Triad/Interval combination to describe 7th chords. We have now seen the Major and Dominant 7th's, so now we will look at the Minor 7th chord. Minor 7th chords are formed using a Minor Triad/Minor Interval combination. (Notice that the Major 7th is Major/Major, and the Minor 7th is Minor/Minor. This will make it easier to remember.)

As an example, let's form a C Minor 7th chord.

1. A Minor 7th chord is made up of a Minor triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, C.
3. We know that a C minor triad is made up of C, Eb, and G.
4. The Minor 7th Interval above C is Bb.
5. Therefore, the notes C, Eb, G, and Bb make up the C Minor 7th chord.

C Min 7th

Let us follow the same procedure again to form a F Minor 7th chord.

1. A Minor 7th chord is made up of a Minor triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, F.
3. We know that a F Minor triad is made up of F, Ab, and C.
4. The Minor 7th Interval above F is Eb.
5. Therefore, the notes F, Ab, C, and Bb make up the F Minor 7th chord.

C Min 7th

We now expand our chart to include the Minor 7th chord construction. Notice that both the Major 7th and Dominant 7th columns are shaded, being the most common forms of the 7th chord. Again, this shading also helps us to visually see the relationship between the different types of chords.

Here is the chart as applied to a C chord:

Yes, the name of this chord is the Half-Diminished 7th chord. Most people do not acknowledge it's existence, and yet is is a very important chord in music theory. Furthermore, it is not difficult to describe using the Triad/Interval method. It's construction, Diminished/Minor, fully indicates which notes make up the chord (as well as give a clue as to why it is called a Half-Diminished chord).

As an example, let's form a D Half-Diminished 7th chord.

1. A Half-Diminished 7th chord is made up of a Diminished triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, D.
3. We know that a D Diminished triad is made up of D, F, and Ab.
4. The Minor 7th Interval above D is C.
5. Therefore, the notes D, F, Ab, and C make up the D Half-Diminished 7th chord.

D Half-Dim 7th

Let us follow the same procedure again to form a B Half-Diminished 7th chord.

1. A Half-Diminished 7th chord is made up of a Diminished triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, B.
3. We know that a B Diminished triad is made up of B, D, and F.
4. The Minor 7th Interval above B is A.
5. Therefore, the notes B, D, F, and A make up the B Half-Diminished 7th chord.

B Half-Dim 7th

We will now add to our chart the Diminished/Minor construction of the Half-Diminished 7th Chord. Please note that the symbol for the Half-Diminished Chord is a circle with a line through it (i.e., Bb Half-Diminished 7th is Bb^ø7). You may not have this "slashed circle" on your keyboard, so a common way to write the chord is also "Bbmin7-5". This rather long way of writing the chord name means, "Start with a Bbmin7 chord, and flat the fifth." When hand writing chord symbols, most people prefer the "slashed circle" method, but most printed music and lead sheets will use the longer, "min7-5" description. (This also brings up an interesting observation: the only difference between a Minor 7th chord and a Half-Diminished 7th chord is that the latter has a flatted fifth.)

Here is the chart as applied to a C chord:

The Diminished 7th chord (which is sometimes referred to as the "Fully" Diminished 7th chord in order to differentiate between it and the Half-Diminished 7th chord) is the "lowest" chord arrangement possible for 7ths. Each note is stacked a minor 3rd above the previous note.

The mere mention of this chord scares many people, simply because they do not understand it. It is a very versatile chord, however, with a variety of uses (especially in chord progressions and substitutions). This amazing chord even occurs four times in the hymn The Old Rugged Cross, although most church pianists never realize it. We describe it as having a Diminished/Diminished construction in the Triad/Interval system.

As an example, let's form an E Diminished 7th chord.

1. A Diminished 7th chord is made up of a Diminished triad, and a Diminished 7th interval.
2. The name of the chord gives us the root, that is, E.
3. We know that an E Diminished triad is made up of E, G, and Bb.
4. The Diminished 7th Interval above E is Db.
5. Therefore, the notes E, G, Bb, and Db make up the E Diminished 7th chord.

E Dim 7th

Let us follow the same procedure again to form an Ab Diminished 7th chord.

1. A Diminished 7th chord is made up of a Diminished triad, and a Diminished 7th interval.
2. The name of the chord gives us the root, that is, Ab.
3. We know that an Ab Diminished triad is made up of Ab, Cb, and Eb.
4. The Diminished 7th Interval above Ab is Gbb.
5. Therefore, the notes Ab, Cb, Eb, and Gbb make up the Ab Diminished 7th chord.

Ab Dim 7th

If you didn't notice in the above example, it is quite common (though not always the case) for a Diminished 7th to have one or more double flats. Now we can add the Diminished/Diminished form of the 7th Chord to our chart, but we are not done yet. We still have one more type of 7th chord to cover.

Here is the chart as applied to a C chord:

We are to the last type of 7th chord! The Augmented 7th chord is often seen as a hybrid between an Augmented chord, and a Dominant 7th chord, because of its Augmented/Minor construction. The Augmented 7th chord is shamefully overlooked by most pianists, for it has an interesting color and appeal. Later, we will examine some of its uses in chord progressions and substitutions.

As an example, let's form a D Augmented 7th chord.

1. An Augmented 7th chord is made up of an Augmented triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, D.
3. We know that a D Augmented triad is made up of D, F#, and A#.
4. The Minor 7th Interval above D is C.
5. Therefore, the notes D, F#, A#, and C make up the D Augmented 7th chord.

D Aug 7th

Let us follow the same procedure again to form a F Augmented 7th chord.

1. An Augmented 7th chord is made up of an Augmented triad, and a Minor 7th interval.
2. The name of the chord gives us the root, that is, F.
3. We know that a F Augmented triad is made up of F, A, and C#.
4. The Minor 7th Interval above F is Eb.
5. Therefore, the notes F, A, C#, and Eb make up the F Augmented 7th chord.

F Aug 7th

In the above examples, notice how some augmented chords will have both sharps and flats in the chord spellings. This is correct spelling for these chords. In the F Augmented 7th example (F, A, C#, and Eb), some would like to write this as F, A, Db, Eb. While the notes would sound the same, the chord would be spelled wrong. ANND ITZ UNOIEENG TOO HAV TWO REED MISPALED WERDZ! Let's see our completed chart:

Here is the chart as applied to a C chord: