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Music Theory

Introduction to Modal Interchange

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Are you getting tired of using the same old chord progressions in your compositions? An excellent way to spice up your creations would be to familiarize yourself with the concept of modal interchange, also known as modal mixture.

To put it simple, modal interchange is the practice of temporarily borrowing chords from a parallel tonality/modality without abandoning the established key. This technique has been around for centuries and is well established in most genres, including rock, pop, jazz and classical music.

Chances are pretty good that you’ve already been using some form of modal interchange, without even realizing it. The Natural Minor key for example, inherently relies on modal interchange to create a strong dominant cadence.


A Little Knowledge is a Dangerous Thing

Before we dive into the topic of modal interchange, I would like to bring up a few points about the age old fear among some musicians that too much theory will somehow make them less creative. Having written this article, I disagree with such an attitude.

In the best of worlds all music would simply write itself. The composer would be able to hear a complete composition with melody, harmonies and chord progression in his head and his only job would be to write it down on paper or record it. Although this might be true for some lucky individuals, such as Mozart, most of us rarely get to experience this.

More often than not, we tend to get stuck or run into problems when composing. This is when having a solid foundation in music theory really comes in handy. It will take much of the guesswork out of the equation and allow you to keep on composing, even when you don’t have that cosmic connection and things are just “pouring out of you”. More theoretical knowledge will equal more possible solutions and ways to be creative. Being able to keep on writing no matter what is an invaluable skill for the professional composer.


Parallel and Relative Tonality

First things first. As stated before, modal interchange means borrowing chords from a parallel tonality, so let’s start by sorting out what constitutes a parallel tonality.

I especially want to make this clear, because the terms relative and parallel tonality have contrasting meanings in different parts of the world. When referring to parallel, I mean tonalities/modalities of any given quality that share the same root. Relative tonalities would share the same set of notes, but with each tonality gravitating towards a different root.

An example of parallel tonalities would be C Major and C Natural Minor. Relative tonalities would be something like C Major and A Natural Minor, that share the exact set of notes. Assuming that all music either is in a major or minor tonality/modality will give us four possible scenarios for modal interchange:

  • Major to Minor
  • Major to Major
  • Minor to Major
  • Minor to Minor

Major to Minor

The most common way to embellish a major key is to borrow chords from some kind of parallel minor. Listen to the two similar chord progressions in G Major written out below.


Chord Scale Choices

So where in the world did that IV-7 chord in bar three come from? Given that we don’t have a melody to take into consideration, we only need to worry about the chord tones of C-7 that are foreign to the key we are in.

Bb and Eb of C-7 are not part of G Major and this reveals that the modal interchange chord must have been borrowed from some kind of parallel G scale with a b3 and a b6 scale degree. Below is a diagram of the parallel functions of all 7 modes of the major scale.

This is an excellent place to start looking for a source to our IV-7 chord. From this list we can find three different theoretical sources that contain a IV-7 chord. Parallel Phrygian, Aeolian and Lokrian all end up with a IV-7 chord when harmonized in thirds.

So how do you chose your source scale and why does it matter? Ultimately this is a personal creative choice, but common practice is to chose the parallel scale that has the greatest number of common tones with the established key. Let’s write out the three choices and examine how many notes they have in common with G Major (Ionian).

Natural Minor (Aeolian) has four notes in common, Phrygian has three, and Lokrian only has two. Our first choice would therefore be Natural Minor, but all three are theoretically possible and would affect the chord scale and available tensions for the IV-7 chord. If we stick to G Natural Minor as our source this will equal a C Dorian chord scale with tensions 9, 11 and 13 available over the IV-7.


Some General Guidelines When Exploring Modal Interchange On Your Own

This wraps up part one of my series on modal interchange. Until next time, try experimenting with the chords from the diagram of the 7 harmonized modes. This is an extensive list that will give you plenty of options for creating new and interesting colors when composing.

Keep in mind that modal interchange chords can be used in different ways. They can replace their diatonic counterpart, harmonize non-diatonic melodies, act as pivot chords for modulation, or serve as a link between two diatonic chords.

Finally, here are several general guidelines to keep in mind when using modal interchange:

  • Make sure that there is no conflict between the melody and the chords.
  • Make sure that the original key is clearly established.
  • Modal interchange chords should be preceded- and followed by diatonic chords.
  • Do not overuse. This could lead to an unwanted modulation or create an ambiguous key center.
  • If using two or more modal interchange chords in row, be careful not to create a cadence to the I chord of the relative Ionian.
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