The Dominant 7th Chord

The Dominant 7th chord is called "dominant" because it is the chord that propels chord changes. It is usually referred to as simply a "7th" chord.(ex.: C7) Almost every song uses a dominant 7th somewhere in it's chord changes. What propels the chord is the tension between the 3rd and 7th notes of the chord. This tension wants to be relieved, often by going to a major chord one fourth higher.

Play G7 to C to hear this.

The Dominant seventh chord is a major triad with a fourth note added a minor 3rd above the fifth of the chord. The interval from the root to the 7th is a minor 7th interval, which is 10 half steps.