This section covers many new chord types which contain four different notes. They are all created by adding one extra note to the various types of triads you learned in section 1.
The most common four note chords are the various types of 7th chords: e.g., Major, minor and dominant 7ths. Seventh chords are created by adding a 7th degree on top of a triad. The type of seventh chord depends on the type of triad, and whether the seventh is natural (e.g., a B note in C major) or flattened (e.g., a Bb note in C seventh). There are also other four note chords such as 6ths and add9 chords. Each of these types is introduced in section 2 with its particular formula and many useful fingerings, along with s demonstrating the use of the chords.