The_Complete_Idiot%27s_Guide_To_Music_Theory

Substitution Example (for the G7 chord)
Diminished chord a third above
Minor 7 chord a fourth below—
over the same root
The more interesting substitutions here are the first one and the last one. The
first substitution replaces the V7 chord with a IV chord; the use of the subdominant
(IV) chord results in a softer lead back to the I chord. The last
substitution uses an altered chord, so that you’re leading back to tonic with a
iim7/V—what I like to call a “Carole King chord.” (That’s because Ms. King
uses this type of harmonic structure a lot in her songwriting.) So if you’re in the
key of C, instead of ending a phrase with a G or G7 chord, you end with a
Dm7/G instead. It’s a very pleasing sound.
Functional Substitutions
Here’s something else to keep in mind. Within the harmonic context of a composition,
different chords serve different functions. The three basic harmonic
functions are those of the tonic, subdominant, and dominant—typically served
by the I, IV, and V chords, respectively. But other chords in the scale can serve
these same functions, even if not as strongly as the I, IV, and V.
For example, the subdominant function can be served by either the ii, IV, or vi
chords. The dominant function can be served by either the V or vii° chords.
And the tonic function can be served by either the I, iii, or vi chords. All these
functions are shown in the following table:
Chord Function Chords
Tonic I, iii, vi
Subdominant ii, IV, vi
Dominant V, vii°
When you have a chord serving a specific function in a composition, you can
replace it with another chord of the same type. So if you have a IV chord, serving
a subdominant function, you can substitute any of the other subdominantfunctioning
chords—the ii or the vi. Along the same lines, if you have a ii
chord, you can replace it with either the IV or the vi.
The same thing goes with the other functions. If you have a V chord, serving a
dominant function, you can replace it with a vii° chord—or vice versa. And a I
chord, serving a tonic function, can be replaced by either a iii or a vi chord—
and also vice versa. It’s actually a fairly easy way to make some simple chord
substitutions.
Chapter 16: Chord Substitutions and Turnarounds 209
Note
Just in case you think you
found a mistake in the preceding
table, the vi chord
can serve both the tonic
and subdominant functions.
It’s a very versatile
chord!