Three or more tones that sound simultaneously are called a
chord. The basic, simplest type of chord is a
triad - a chord of three notes, built upon a root (key-tone or tonic), together with 3rd and 5th above it. Here
are the four different kinds of triad built on
C as a root:
Also called
tertian or triadic harmony, refers to chords built on intervals of thirds. Lets analyse chord built
C major scale:
First chord, which is based on C as a tonic, is a C major 7th chord. There are seven different chords,
one built on each step of major scale. These steps are the roots of seven
modes (scales) of actual major
scale. To understand this, lets analyse the two octave C major ascending scale:
Thus on each mode, using the principle of creation of chords by thirds, the following chords appear:
All these chords are the diatonic seventh chords. They are frequently used in jazz harmony.

The aural basis of tertian harmony is the premonition of resolution at a central chord called tonic or
I chord.
Another chord with the strongest gravitational pull to the tonic is the
dominant or V chord. Next strongest is
subdominant or IV chord. The I, IV, and V chords are primary chords. All other chords are secondary or
related chords because they share tones with primary chords:
The understanding of such relationships between the chords is important to establish tonality (feeling of key)
- gravitation and movement of different chords to a central
tone (or chord) called tonic.

In diatonic music, tones with a sense of finality are called
Rest tones and others with sense of progress to
other tones -
Motion tones.

The rest tones are the 1st, 3rd, 5th, and 8th degrees of the major scale. Motion tones sound as though they
must progress to the nearest rest tones - the 2nd degree of the moving to the 1st or 3rd degree, the 4th
degree of the scale to the 3rd, the 6th degree to the 5th, and the 7th degree to the 8th.
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lesson 5.