Next up on your look at triads is the diminished triad. FIGURE 7.6 shows a C diminished triad.
Break down the intervals in the C diminished chord. Start with the interval from C to E, which is a minor third. The next interval, from E to G,
FIGURE 7.6 C Diminished Triad
is also a minor third. The intervallic pattern of this triad is minor third, minor third. This is important to note, because both intervals are minor thirds. Both the major and minor triads contain one of each third (one major third, one minor third), albeit each triad had the thirds in different order. The diminished triad has the same thirds (both minor). Think of it this way: Each triad contains two thirds, and there are only major and minor thirds to choose from. You can have two triads that use one major third and one minor third (in reverse order), and that gives you two possible triads (major and minor). If you use the same third twice, you can get two more triads. In the case of using two minor thirds, you get a diminished triad. You will see shortly what happens when you use two major thirds.
The diminished triad is used more in classical music than in popular music, although it is found in certain popular songs. A great example is “Michelle” by the Beatles, which uses a diminished chord in its harmony. Check out the sheet music to see where it is.
The naturally occurring scales are the major and minor scales. The other scales have been either created or are outgrowths of the major scale. Chords can be constructed solely on intervals, or they can be related to scales. As you will see shortly, they also can be derived from scales. The three triads you have explored thus far—major, minor, and diminished—occur naturally in music because of their relationship to scales. The final triad, augmented, is not a naturally occurring triad from any major or minor scale.
An Alternative View for Diminished Triads
Start off by looking at all the intervals in the C diminished triad, all measured from C.
The interval from C to E is a minor third.
The interval from C to G is a diminished fifth.
The diminished triad is the first time you see a fifth in a chord that isn't perfect. That could explain why the diminished triad has an unusual sound when compared to the major and minor triads.
Although there is a diminished scale, most musicians don't correlate the spelling of a diminished triad to that of the diminished scale, even though the first, third, and fifth tones of that scale can be used to form the chord. The reality is that unless you are a jazz improviser, you probably won't deal with the diminished scale except in theoretical understanding. For most of us, the derivative approach makes the most sense. If a C major triad is C–E–G and a C diminished chord is spelled C–E, then you can derive the following rule: To turn any major triad into a diminished triad, lower the third and fifth one half step.
You could alternatively derive the answer from the minor triad (1, 3, 5): To turn any minor triad into a diminished triad, lower the fifth one half step.