How to Change Keys by Switching Tonics on the Guitar
You may think of music on the guitar as having a main chord called the tonic, as well as a parent scale that the tonic and the rest of the chord progression are drawn from. However in many songs the tonic changes at some point, and sometimes the parent scale changes too.
Technically, a key change is a change from one tonic or tonal center to another. This may or may not also include a change in key signature on a written score. So when you come across a chord that doesn’t fit into the same key as the other chords it’s played with, you need to look elsewhere to figure out where it comes from.
Note: The use of modal interchange and borrowed chords usually revolves around a consistent tonic, so these types of techniques aren’t considered key changes in the classic sense, though they do employ the use of other scales.
The first type of key change that you play is one where the tonic changes but the parent major scale stays the same. A perfect example of this is when a song switches between being centered on the relative major and being centered on the relative minor, though songs can switch between other scale degrees, too.
Basics of switching between relative major and minor
Here is a series of changes that first center on an Am chord and then switch to the relative major, C. Here, the Am is chord vi from the C major scale and the C chord is I.
“Mr. Jones” by Counting Crows switches in a manner similar to this. It starts out centered on the vi chord, Am, in the C major scale but switches to the I chord, C, at the chorus. U2’s “Staring at the Sun” also switches from Am to C from verse to chorus. “D’yer Mak’er” by Led Zeppelin does the opposite, starting out on C then switching to Am during the chorus.
Basics of switching between other scale degrees
Sometimes a song switches between scale degrees other than the relative major and minor. For example, “Landslide” by Fleetwood Mac, which is played with a capo at the 3rd fret, using G major chord shapes, first focuses on the IV chord (an open C chord shape) before later settling on the I chord (an open G chord shape).
The modulation in “Landslide” is a change from Lydian to Ionian. You hear the same type of change from IV to I in various scales in “Just Remember I Love You” by Firefall, “Here Comes my Girl” by Tom Petty, “Man on the Moon” by R.E.M., “Hey Jealousy” by Gin Blossoms, and “Space Oddity” by David Bowie.