The next step is to learn extended chords. Extended chords are chords that contain additional notes on top of the normal triads. Western music is based on a system of tonality called tertian harmony because all the chords are based on the interval of a third. A third interval is between the root and the third, and another third interval is between the third and the fifth. The third interval is the essential building block of chords and harmony.

To extend chords beyond their basic three-note structures, you simply add another third on top. Just as you did in the previous example, you use only notes from the parent scale. When you use only notes from one scale to make chords you are using that scale “diatonically,” which means “from the scale.” Because extended chords contain four or more notes, they are commonly referred to as tall chords, because they occupy more of the staff than simple chords do.

Seventh Chords

When we harmonized the scale again, we created seventh chords. Why seventh chords? Because the highest note in each chord is seven notes away from the root. Chord names are very literal, even though they can sound like calculus coordinates. Look at FIGURE 8-8 showing the C-Major scale harmonized in sevenths.

From this figure you form a bunch of new chords: major seventh, minor seventh, half-diminished seventh, and dominant seventh. Tab was not included with this figure because these chords are not playable on guitar. Due to the guitar's tuning, not all combinations of notes are possible; you also only have four fingers. FIGURE 8-9 shows the same harmonized scale, but this time guitar–friendly (or idiomatic) voicings are used in the notation and the tab.

The notes in these chords are the same as in FIGURE 8-8; however, the order of the notes has been shifted around. When you play these chords, realize that you haven't left C Major; all the chords are based on combinations of notes from the C-Major scale, again diatonic notes. Try substituting seventh chords for the simple triads you may be already playing. For instance, in your I-vi-IV-V song, you can use the same numbers; just substitute the new seventh chords.

Modern rock bands like Incubus and the Foo Fighters have used extended seventh chords in their music. Pink Floyd has also used extended chords in their music.

How to Read Chord Symbols

Now that you can play a few extended chords, let's look at examples of how extended chords are written in music:.

• Major seventh chords are written as: CM7, Cmaj7, Cmajor7, or C 7.

• Minor seventh chords are written as: Cm7, Cmin7, Cminor7, or C-7.

• Dominant seventh chords are written as: G7 or Gdom7. If there's just a letter and the number 7, you know it's a dominant seventh chord.

• Full-diminished chords (less commonly found in rock and blues) are written as C°7. If you don't see the number seven after the degree sign, it's just a simple triad.

• Half-diminished chords are written as: Cø7. The normal diminished circle is cut in half.