When more than two pitches are stacked together the resulting harmony is called a chord. As we have already learned, the simplest type of chord is a triad. The prefix "tri" means three, so a triad is a chord composed of three pitches. The pitches that compose a triad are the 1st, 3rd and 5th intervals in relation to the root. When a fourth pitch is added to a chord, it is referred to as a seventh chord. The added pitch is and interval of a seventh from the root, which is the reason for the name.
The four pitches of a seventh chord can be stacked in different orders. When the root is on the bottom the chord is said to be in root position. When the third is on the bottom the chord is in 1st inversion. When the fifth is on the bottom the chord is in second inversion. When the seventh is on the bottom the chord is in third inversion.
The intervals between the four pitches of a seventh chord determine the quality of the chord. These quality defining intervals are measured with the root position version of the chord. Seventh chords can be labeled as having major, minor, dominant, half diminished or diminished qualities.
Major seventh, dominant seventh and minor seventh chords all contain a perfect fifth. A major seventh chord contains a major third and a major seventh. It is a major triad with a major seventh added. A dominant seventh chord contains a major third and a minor seventh. It is a major triad with a minor seventh added. A minor seventh chord contains a minor third and a minor seventh. It is a minor triad with a minor seventh added.
There are two types of diminished seventh chords. Both contain diminished fifths and minor thirds, so they are both diminished triads with sevenths added. The half diminished seventh chord has a minor seventh added to the triad. The other name for this chord is a minor 7 flat 5, because it is identical to a minor seventh chord aside for the flatted fifth. The fully diminished seventh chord has a diminished seventh added to the diminished triad. A diminished seventh is two half steps lower than a major seventh or one half steps lower than a minor seventh. It is the enharmonic equivalent to a major sixth, but is identified as a diminished seventh since its pitch letter is the seventh pitch from the root. An example of this would be the interval between C and B double flat. Since the pitch is being identified as B double flat, instead of its other name of A, the interval is labeled as a diminished seventh.
The major seventh and dominant seventh chords can both posses a raised fifth since they both contain major thirds. This causes them to become augmented triads with an added major or minor seventh. These chords retain their identities as either major or dominant seventh chords. They are labeled as altered seventh chords, and the alteration of the raised fifth is added to the name (Major 7 #5 or Dom 7 #5).
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Ray Melograne received his BA and ME in music education from Queens College. He is currently teaching music in the NY public schools. He also teaches privately on the Zoen.com network.