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The Key to "Key Changes"

We have already seen the difference between Notes that are Diatonic and those which are Chromatic.

This same distinction exists for Chords as well. In other words, we can have "Diatonic" Harmony and "Non-Diatonic" (or "Chromatic") Harmony.

Whenever we start using Chords that are outside of a given Key, it is generally referred to as a "Key Change". There are two types of Key Changes:

1. Tonicization
2. Modulation

Tonicization (also sometimes known as "Modal Interchange" or "Mode Mixture") - This is to use Chords from two different Keys at the same time. These are called "Borrowed Chords". [There are specific reasons as to why these types of Chord Substitutions work, and we will cover some of them elsewhere. It often has to do with the relationship of the Harmonic Intervals inside of the Chords.]

Modulation - This is usually what people are referring to when they use the term "Key Change". It is when an entire piece of music seems to switch from being within one Key into another, entirely different Key.

To be a little more specific, Tonicization is to briefly dip into another Key here and there, whereas Modulation is when an entire Chord Progression + Cadence is in another Key. [Some people use these terms a little differently, but these definitions will serve us well.]

Tonicization can be accomplished by playing a Non-Diatonic Chord between two Diatonic Chords in order to connect them together. This is called a "Passing Chord". We are simply "passing through" one Key without fully immersing ourselves within it.

Modulation can be accomplished in two different ways...

1. "Direct" or "Abrupt" Modulation - This is to just switch directly into another Key. As it's name implies, it can be quite abrupt. You can hear this type of Key Change very distinctly. It is also sometimes called a "Truck-Driver Modulation" for this reason. The abrupt switch is like the jerking motion that a truck makes when shifting gears. [If you would like an example, the song "Love On Top" by Beyoncé is a good one. Starting at about 3 minutes into the song, everytime she repeats the lyrics it audibly moves into another Key.]

2. "Indirect" or "Telegraphing" Modulation - This is to switch into a another Key smoothly, gradually. This is often done by playing "Pivot Chords", which are Chords that are shared by both Keys. They can help us to "pivot" from one Key into another.

With any type of Modulation, we usually consider the Interval that is formed between the Tonic of the Key that we are starting in and the Tonic of the Key that we are shifting into. This is called the "Modulation Distance".

In the context of The Tonal System, looking at The Circle of Fifths is helpful. Find your starting Key on it. The Keys around it on the diagram are some of the most common ones to Modulate into from that Key. [Generally, the larger the Modulation Distance, the more rarely it occurs within music, especially Pop music.]

A simple way to learn how to Modulate is to look at the Notes that are shared between Relative Keys or Parallel Keys. Are there any Pivot Chords between them?