Triads · Music theory
How a chord is built, the four triad qualities, their inversions and how to recognize them.
What a chord is
A chord is a combination of three or more different notes sounding together. In tonal music chords are built by stacking thirds. The triad has three notes: the root, which gives it its name, the 3rd and the 5th.
C–E–G is the triad on C: C is the root, E its 3rd and G its 5th. It is the same chord with the notes one after the other (arpeggiated) as together (blocked).
The notes of a triad are named by their distance from the root, not by the order in which they sound. E is the 3rd of C major even when it is in the bass, and G is its 5th even when it is at the very top.
Close and open position
A chord does not change identity because of how its notes are spread. In close position its upper notes are as near together as possible; in open position, another chord note would fit between them. The piano usually has close position in the right hand and choral harmony, a mixture of both.
Since a triad has three notes and a choir four voices, one must be doubled. In root position it is normal to double the root, and never the leading tone, which has an obligatory resolution. Zarlino, in the 16th century, theorized the triad as the basis of harmony, and Johannes Lippius called it the harmonic triad in 1612.