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The dominant seventh chord is a musical chord composed of a root, a major third, a perfect fifth, and a minor seventh. In other words, it is a major triad with the addition of the minor seventh of the root of the chord. In musical chord notation, the symbol that denotes a dominant seventh is created by placing a "7" immediately following the letter designating the chord. The "7" is sometimes printed in superscript font.
The structure of a dominant seventh chord may be referred to as a major triad with an added minor seventh. The note that forms the base of the chord is called the root. The root is the note upon which the other three notes of the chord are built. Musicians sometimes refer to a dominant seventh chord as simply "a seventh," although technically, that description could refer to a variety of seventh chords.
The first step to building a dominant seventh is to form a major triad. Once the triad is formed, the seventh of the root can be added. To build the major triad, take the root note and add a major third and a perfect fifth. For example, to build a major triad on G, play a G alongside the major third, which is B, and the perfect fifth, which is D. Then, to complete the chord, add the minor seventh of the root, which in this case would be an F.
Another way to think about a dominant seventh is through half steps. In this case, one could say that the chord is built by playing the root note plus a note four half-steps up from the root, plus a note seven half-steps up from the root, plus a note ten half-steps up from the root. In other words, the chord is formed by playing the root, a note four half-steps up from the root, another note three additional half-steps up, and a final note an additional three half-steps up from the last.
Because the fourth note in the chord, the minor seventh, is at a dissonant interval from the root, the dominant seventh is known as a chord that sounds "restless" or in need of resolution. There are several ways in which the chord can be resolved. One of the most popular way to create resolution involves a major or minor triad whose root is a fifth below the root. An alternative resolution that is often equally effective is a minor triad that is a major second above the root of the original chord.