Recommended resources
The freely available resources this lesson will direct you to.
Welcome to your next lesson. In our previous session, we stepped outside the box of traditional harmony to explore the open, atmospheric sounds of quartal and quintal chords. You learned to build harmony by stacking fourths and fifths, creating voicings that are central to modern guitar styles.
Today, we return to the familiar world of tertian harmony (chords built from thirds), but we're going to give it a powerful, modern twist. We will investigate a technique that is fundamental to creating rich, emotionally complex chord progressions that surprise the listener while still feeling logical. This technique is called modal interchange.
Your learning outcome for this lesson is to identify the diatonic chords of a major key and its parallel minor key as a basis for modal interchange. We will first systematically map out the chords available in a major key, then do the same for its parallel minor, and finally see how "borrowing" chords from the minor key can transform a major key progression.
Part 1: The Diatonic Chord Palette
In music theory, a "key" provides a specific set of notes—a scale. From this scale, we can build a corresponding set of chords. These are called diatonic chords. You can think of the diatonic chords of a key as the default toolkit or "standard library" of harmonies available for that key. Every chord in this set is built exclusively from the notes of the parent scale, which is why they all sound cohesive together.
To understand this process, let's first review how these chords are built and categorized. The following reading provides an excellent foundation.
Diatonic Chords You Need To Know (Triads and 7th Chords)
This article from Learn Jazz Standards breaks down the concept of diatonic harmony. It explains how chords are built from scales and introduces the Roman numeral system used to analyze them.
Please read the following parts: Start with the introduction, from the definition of diatonic chords down to the first table of contents. Next, read the section on Roman numerals, which explains how we label chords within a key. Finally, skip down to the section on Diatonic Seventh Chords. Read from the beginning of this section, covering 7th chords, as these are the most relevant voicings for the styles you're aiming for. Pay close attention to the qualities of the chords (major 7th, dominant 7th, minor 7th, and half-diminished).
As you've just read, harmonizing the C major scale with seventh chords gives us the following palette:
- I: Cmaj7
- ii: Dm7
- iii: Em7
- IV: Fmaj7
- V: G7
- vi: Am7
- vii°: Bm7(b5) or B half-diminished
This specific sequence of chord qualities (maj7, m7, m7, maj7, 7, m7, m7b5) is the same for every major key.
Part 2: The Parallel Minor Universe
Now, let's introduce the concept that unlocks modal interchange: the parallel key.
- Parallel keys share the same starting note, or tonic. For example, the parallel minor of C major is C minor.
- This is different from a relative key, which shares the same notes and key signature. The relative minor of C major is A minor.
Because C major and C minor start on the same note but use different scales, they generate different sets of diatonic chords. This gives us an entirely new palette of chords to work with, all while maintaining C as our tonal center.
The C natural minor scale consists of the notes: C, D, E♭, F, G, A♭, B♭.
Harmonizing this scale gives us this set of diatonic seventh chords:
- i: Cm7
- ii°: Dm7(b5)
- ♭III: E♭maj7
- iv: Fm7
- v: Gm7
- ♭VI: A♭maj7
- ♭VII: B♭7
This is the "standard library" for the key of C minor. The next reading clearly lays out the two palettes side-by-side, which is the core of today's learning outcome.
This article from StudyBass defines borrowed chords and shows the direct comparison we need.
Read the introductory sections defining the concept and its alternative names, "modal interchange" and "mode mixture." Now, focus on the table under the heading Major + Minor Diatonic Chords. This table is the crucial part of this lesson. It places the diatonic chords of C major and C minor together, allowing you to directly compare them and see the source of our "borrowed" chords.
Take a moment to compare the two sets of chords from that table. Notice the powerful differences:
| Degree | C Major Chord | C Minor Chord |
|---|---|---|
| I/i | Cmaj7 | Cm7 |
| IV/iv | Fmaj7 | Fm7 |
| V/v | G7 | Gm7 |
| VI/♭VI | Am7 | A♭maj7 |
| VII/♭VII | Bm7(b5) | B♭7 |
These differences are the source of the magic. You can be playing a song in C major and suddenly introduce an A♭maj7. To the listener's ear, this is an unexpected but beautiful color that temporarily darkens the mood before resolving back to the brighter major key. You are "borrowing" the ♭VI chord from the parallel minor.
Part 3: Hearing Modal Interchange in Action
Theory is one thing, but hearing these substitutions is what makes the concept click. The video below provides excellent musical demonstrations of borrowing chords from the parallel minor.
Writing Progressions with Borrowed Chords: Songwriting Lesson [MUSIC THEORY - MODAL INTERCHANGE]
This video from Signals Music Studio is a fantastic practical guide to using borrowed chords in songwriting.
Watch the first section from the introduction, where the host explains the concept and demonstrates borrowing the ♭VI chord (A♭ major) in a C major progression. Listen to the dramatic effect this single chord has. Next, skip forward and watch the section from discussing common borrowed chords. He demonstrates the minor iv chord (Fm in the key of C) and the iiø7 (D half-diminished), which are two of the most popular and effective borrowed chords.
The key insight here is that by knowing the diatonic chords of both the major key and its parallel minor, you essentially double your harmonic vocabulary for any given tonic. You have two distinct palettes to pull from, allowing you to create more dynamic and emotionally resonant music.
Your Task
Now it's your turn to apply this system. Let's work in the key of G major.
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Map the Palettes:
- First, write down the seven diatonic 7th chords of G major (Scale: G-A-B-C-D-E-F#). Use the major key formula (Imaj7, iim7, iiim7, etc.).
- Next, write down the seven diatonic 7th chords of its parallel minor, G minor (Natural Minor Scale: G-A-B♭-C-D-E♭-F). Use the minor key formula (im7, ii°7, ♭IIImaj7, etc.).
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Analyze and Compare: Look at your two lists. Identify three chords that have the same root but a different quality. For example, the IV chord in G major is Cmaj7. What is the iv chord in G minor?
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Spot the Borrowed Chord: The progression from Radiohead's "Creep" is
Gmaj7 – B7 – Cmaj7 – Cm7.- Which key is this progression primarily in?
- Identify the one chord in this progression that is "borrowed" from the parallel minor key. Which Roman numeral would you use to label it? (e.g., I, ♭VI, iv, etc.)
This exercise solidifies your ability to identify the chord palettes that are the foundation for modal interchange.
Conclusion
Today you've established a systematic way to expand your harmonic options. By understanding the diatonic chords that belong to a major key and its parallel minor, you've unlocked the ability to use modal interchange, a technique at the heart of modern harmony.
Key Takeaways:
- Diatonic chords are the native chords built from a key's scale.
- Parallel keys (e.g., G major and G minor) share a tonic but have different scales and therefore different diatonic chords.
- Modal interchange is the practice of borrowing a chord from the parallel minor to use in a major key progression (or vice versa).
- This technique adds emotional depth and harmonic interest, with common borrowed chords being the minor iv, ♭VI, and ♭VII.
In our next lesson, we will build directly on this foundation. You'll learn how to apply modal interchange in practice, focusing on how to smoothly introduce and resolve a borrowed chord within a progression, using the example Cmaj7 - Fmaj7 - Abmaj7 - G7.