The_Complete_Idiot%27s_Guide_To_Music_Theory

Altering the Bass
Here’s another neat way to make old chords sound new—and all you have to do
is change the note on the bottom of the chord.
Back in Chapter 9 we touched briefly on the concept of slash chords, more properly
called altered bass chords. With an altered bass chord, the top of the chord
stays the same; but the bass, as the name implies, is altered.
Some folks call these chords slash chords because the altered bass note is indicated
after a diagonal slash mark, like this: G/D. You read the chord as “G over
D,” and you play it as a G chord with a D in the bass.
Examples of slash chords.
You can use altered bass chords to achieve several different effects, including
the following:
◆ By putting one of the three main notes (but not the root) in the bass, you
dictate a particular chord inversion.
◆ By treating the bass note as a separate entity, you can create moving bass
lines with increased melodic interest.
◆ By adding a nonchord note in the bass, you create a different chord with a
different harmonic structure.
Slash chords are used a lot in jazz, and also in more sophisticated popular
music. Listen to Carole King’s Tapestry album and you’ll hear a lot of altered
bass (she’s a big fan of the minor seventh chord with the fourth in the bass); the
same thing with a lot of Beach Boys songs, especially those on the legendary Pet
Sounds album.
Two Chords Are Better Than One
An altered bass chord uses a diagonal slash mark to separate the chord from the
bass note. When you see a chord with a horizontal line between two different
notes, like a fraction, you’re dealing with a much different beast.
This type of notation indicates that two chords are to be played simultaneously.
The chord on top of the fraction is placed on top of the pile; the chord on the
C
bottom is played underneath. For example, when you see you know to play
G
a C Major chord on top of a full G Major chord.
Chapter 16: Chord Substitutions and Turnarounds 205