Example of a Key Change

Here is an example of a key change:

Victor Zuckerkandl's The Sense of Music

It comes from Victor Zuckerkandl's The Sense of Music. From 1959, the book is a classic introduction to music from a theoretical point of view. The author does not identify the melody he uses as an example, but it sounds like an old hymn tune.

The key change (which the author calls a movement of the "tonal center") occurs in measure 11, where an eighth note on G is sharpened to G♯. Zuckerkandl prefers to apply the terms "key" and "key change" to whole pieces of music and to large sections thereof, respectively. When the tone around which other tones revolve and to which they are dynamically drawn changes only briefly, as here, the tonal center is said to "move."

The movement of tonal center happens as the direct result of playing G♯ (G sharp), instead of G, just before the new tonal center, A. At this point, says Zuckerkandl, "the ear feels a light shock." Then in the next measure (measure 12) we hear A, G♯, and A again, this last note being a half note with a fermata above it for extra emphasis.

Meanwhile, the original tonal center or key of the music, the tone D, has been conspicuously absent since being sounded as the first note in measure 7. But when G♮(G natural) is played instead of G♯ in measure 15, the ear knows to expect its reappearance as the destination toward which the other tones of the piece are proceeding — which amounts to a definition of "tonal center."

And, indeed, the piece ends on D, just as it should.

The reason the sequence G♯-A works to shift the tonal center is that G♯ is 7 (the seventh degree) and A is 8 (the eighth degree, or the octave of 1) in the A Major scale. 7 is the "leading note" of a scale. Played in conjunction with 8, it tells the ear that 8 is the tonal center.

When the ear hears G from the original scale of the piece sharpened to G♯, and then hears A, it tends to lock into the idea that a (new) 7-8 sequence has just been played, and the second note ought now to be considered the new tonal center. This is especially true when the original tonal center has been missing in action for some time.

One of the lessons here is that it is easy for the composer to move the tonal center, when desired. It does not require any elaborate buildup, at least in a simple melody such as this one. (Though this is one of the simplest ways to move the tonal center, there are other, more elaborate ways as well.)

Another lesson is that (with the exception of switching from a major key to its "relative minor" or vice versa) key changes or tonal center movements require accidentals (sharp or flat signs) in the score. That makes them stand out — though not all accidentals in a score imply a key change, by any means.

A third lesson is that the ear picks up on tonal center shifts automatically and easily, whether or not the rest of the mind can put a name to what has happened.