To start with, let's examine what a dominant seventh chord is. In its basic form, this chord has four different notes sounding simultaneously, with the spacing of three, three and four semitones between each of its notes (going from the lowest note to the highest note). Here is a list of twelve different dominant seventh chords:

G, B, D and F

G#, B#, D# and F#

A, C#, E and G

Bb, D, F and Ab

B, D#, F# and A

C, E, G and Bb

C#, E#, G# and B

D, F#, A and C

Eb, G, Bb and Db

E, G#, B and D

F, A, C and Eb

F#, A#, C# and E

The above twelve chords belong to the following major and minor keys respectively: C, C#, D, Eb, E, F, F#, G, Ab, A, Bb and B.

The chords are called dominant sevenths because their bottom note starts on the fifth degree (called the dominant) of the scale. They also have a top note placed seven letters above the bottom note; hence, the word seventh appears in dominant seventh. For example, our first above listing is G, B, D and F. G is the fifth note in C major or C minor. As well, the F is seven letters above the bottom G (G, A, B, C, D, E and F? we count all of the letters including the G and F).

Dominant seventh chords are popular for a number of reasons. They are versatile in that they can be effectively stacked into a more complex chord. Again, let's use the first listing to demonstrate this. If we add another note overtop of our first chord, we get the following: G, B, D, F and A. This is called a dominant ninth chord. Similarly, we can build eleventh and thirteenth chords by using the same stacking technique. Dominant chords of this variety, when arranged skilfully, open the door to a whole new harmonic vocabulary in many styles of jazz.

Dominant sevenths also play a significant roll in different types of cadences. A cadence is a chord progression at the end of a music phrase, section or composition. The most common progression involving a dominant or dominant seventh chord is a 5-1 (called a perfect) cadence. Other common chord sequences involving dominant and dominant seventh chords include the following:

?2-5-1

?1-4-5-1

?3-6-2-5-1

The five in the above chord progressions signifies a dominant chord, which is often substituted with a dominant seventh, ninth, eleventh or thirteenth chord. As a final note, dominant seventh, ninth, eleventh and thirteenth chords are easily altered by raising or lowering the fifth and/or ninth note degree of the chord.