Basic Chord Theory
In their simplest form, chords all contain three notes. These notes are referred to as roots, thirds, and fifths, which indicate how far away the intervals are from the root. Take for example a C-Major chord consisting of the notes C, E, G. C is the root, the note E is a third away from C, and G is a fifth away from C. Every interval in a chord is measured away from the root, or name, of the chord. All simple triads contain roots, thirds, and fifths. In the case of a major chord, the triad contains a root, a major third, and a perfect fifth. Look at FIGURE 8-5 to see the intervals.
To find a simple major chord, all you have to do is take the first, third, and fifth notes of the major scale that shares the root. For example, to find an E-Major chord, write out the notes of an E-Major scale (E, F, G, A, B, C, D, E) and select the first (E), the third (G), and the fifth (B). That's an E-Major chord. Try it with a few keys for practice.
How do you form a minor chord? All you have to do is lower the third one half step (or one fret) of any major chord. Let's use E Major again as an example. The notes for an E-Major triad are E, G, B. Using the rule of lowering the third, lower the G to G. Now you have an instant E-minor chord: E, G, B. This works with any chord. Think of your open-position E-Major and E-minor chords—the only finger that changes is the third. You could also spell the minor scale, and play its first, third, and fifth note; either way works. Practice both so your ability to spell scales and chords is strengthened in all facets.
The Other Triads
Classical, jazz, and popular music contain diminished chords. Blues music rarely uses diminished chords, because they are not part of the standard twelve-bar blues progression; however, some rock music does use diminished chords. To make a diminished chord, start with the major chord first and lower the third and fifth. Let's use E again: From E Major (E, G, B), lower the G to G and the B to B. The notes for an E diminished are E, G, B.
The final triad is called an augmented triad. Augmented triads are fairly rare in rock music, although they do come up. (You hear them a lot in jazz and classical music.) An augmented triad is a major triad with a raised fifth. For a C augmented, start with the basic major triad (C, E, G), and raise the fifth G up one half step to G, giving you a C-augmented chord (C, E, G). Augmented chords do not naturally occur in the harmonized major scale. Nonetheless, they are important to understand.
Swedish guitarist Yngwie Malmsteen often uses the diminished chord in his music. Frank Zappa and Steve Vai have also used augmented chords.