When more than two pitches are stacked together the resulting harmony is called a chord. 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.
A root is the primary pitch of a triad. The name of this pitch becomes the name of the triad, so if you want to construct a triad centered around the pitch C you would be making a C triad. In this example C would be the 1st interval and the other two pitches would be the 3rd and 5th of C (which are E and G).
The three pitches of a triad can be stacked in different orders. When the root is on the bottom the triad is said to be in root position. When the third is on the bottom the triad is in 1st inversion. When the fifth is on the bottom the triad is in second inversion.
The intervals between the three pitches of a triad determine the quality of the chord. These quality defining intervals are measured with the root position version of the triad. Triads can be labeled as having major, minor, diminished or augmented qualities.
Triads in which the root and fifth are a perfect fifth apart are either major or minor. With these two cases a major triads possess a major third between the root and third. Minor triads possess a minor third between the root and third.
In root position, a diminished triad is composed of a diminished fifth (between the root and fifth) and a minor third (between the root and third). This results in a stack of minor thirds. An augmented triad is composed of an augmented fifth (between the root and fifth) and a major third (between the root and third). This results in a stack of major thirds.
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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.