The_Complete_Idiot%27s_Guide_To_Music_Theory

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Part 3: Tunes
Note
In classical music theory, a
power chord is called an
open fifth, and is technically
an interval, not a
chord.
Power chords, up and down the scale.
The resolution from the perfect fourth to the major third is just a half-step
movement, but that little half step makes a world of difference; until you make
the move, you’re sitting on the edge of your seat waiting for that incredible
tension to resolve.
Power Chords
If you want a really simple chord, one with a lot of raw power, you can play just
the root and the fifth—leaving out the third. This type of chord is called a power
chord; it is noted by adding a “5” after the chord note. (For example, a G power
chord is notated G5, and includes only the notes G and D.) Power chords are
used a lot in certain types of popular music, in particular the hard rock and
heavy metal genres.
Here’s one bad thing about power chords: If you use a bunch of them in a row,
you create something called parallel fifths. As you’ll learn in Chapter 14, parallel
fifths are frowned upon, especially in classical music theory. So use power chords
sparingly and—if at all possible—not consecutively.
Inverting the Order
Although it’s easiest to understand a chord when the root is on the bottom and
the fifth is on the top, you don’t have to play the notes in precisely this order.
Chords can be inverted so that the root isn’t the lowest note, which can give a
chord a slightly different sound. (It can also make a chord easier to play on a
piano, when you’re moving your fingers from chord to chord; inversions help
to group the notes from adjacent chords closer together.)
When you rearrange the notes of a chord so that the third is on the bottom
(3-5-1), you form what is called the first inversion. (Using a C Major chord as an
example, the first inversion is arranged E G C.) The second inversion is where you
put the fifth of the chord on the bottom, followed by the root and third (5-1-3).
(Again using C Major as an example, the second inversion is arranged G C E.)
The standard triad form, with the root on the bottom, is called the root inversion.
The first and second inversions of a C Major chord.