  
Introduction
As we have already learned, two pitches sounding simultaneously
is a harmonic interval. Three or more pitches sounding simultaneously
is a chord.
Although chords can be built by stacking
intervals of any size, those built in thirds are the most common.
Following are examples of various chords:

1
Triads
Most of the harmony we encounter in Western culture
is based on triads. This is called tertian
harmony and was standard from about
1600 to 1900. A triad is a three-note
chord built in thirds. Examples of all the triads built on the white
keys of the piano are shown below:

Every triad consists of three
components: a root, a third,
and a fifth. The root is the
tone from which the chord is both constructed and named. The following
chord, therefore, is a G chord.

  
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