A borrowed chord can be thought of as a chord taken from a key, or harmonised scale, parallel to the predominant key and scale of the progression.
In music, "parallel" basically translates to "on the same root or tonic note".
So C major and C minor, for example, are both parallel, whether in the context of chords, scales or keys. They both share the same root of C and can be interchanged on that note.
Since chord progressions (and therefore keys) are most typically derived from a harmonised scale (the most common being the major and minor scales), we can effectively "borrow" chords from any degree of a parallel scale (or mode) as a means of creating more harmonic diversity and variation.
By understanding and training your ears to the most common borrowed chords, you'll be able to more easily spot the non-diatonic or "outside" changes that occur in a lot of music.
Furthermore, by connecting them to the harmonised scales from which they're borrowed, you'll also have a better idea of when to switch patterns for lead accompaniment, bringing everything together into a functional approach for both harmony and melody.
The Function of Borrowed Chords
Borrowed chords essentially involve a temporary change of implied scale, because we're taking (borrowing) a chord from a degree of a scale other than that which the overall key is centered around.
But what distinguishes a borrowed chord from an outright key change (modulation), is that we don't lose a sense of the original tonic or key center. The change is transitory and integral enough to the original key center that the original tonic, whether major or minor, remains our "home". So we can borrow from a parallel minor key, yet still remain in a major key (and vice versa).
Take this example in the key of C major...
Cmaj / Em7 / Am7 / Fmaj ( I / iii / vi / IV )
We're now going to substitute the iii and IV with the following (underlined)...
Cmaj7 / D7 / Am7 / A♭maj7 ( I / II / vi / ♭VI )
While all the chords in the first example were derived from the harmonised C major scale, the second example involved chords borrowed from two parallel scales - namely C Lydian and C minor/Aeolian respectively.
However, notice how the overall sense of returning home to the original tonic wasn't disrupted by these "outside" changes. There was still a natural gravitation towards the C major tonic as our center.
So the borrowed chord's primary function is not to change the key (i.e. modulation), rather create an alternate or "outside" journey around an existing tonic. This not only offers some interesting possibilities when looking to add variation to your progressions and make the journey less predictable - it also indicates when a change of scale is necessary to accompany such changes melodically.
Let's break down the most common examples we're likely to come across in a major key.
Natural Minor / Aeolian
A while back I created a summary lesson (with video) covering borrowed chords from the parallel natural minor scale.
The natural minor scale (also called Aeolian) is arguably the most common reference scale for borrowed chords in a major key. Here are both the major and minor scale chords (both triad and seventh) in parallel, referencing C as the tonic...
Since we covered examples in the above lesson, I'll refrain from repeating myself too much! But the summary here is that the parallel minor scale gives us common substitute/supplementary chords such as...
2nd degree diminished or ii (e.g. Dm7♭5)
Flat 3rd degree major or ♭III (e.g. E♭)
4th degree minor or iv (e.g. Fm)
5th degree minor or v (e.g. Gm)
Flat 6th degree major or ♭VI (e.g. A♭)
Flat 7th degree major or ♭VII (e.g. B♭)
Any of these chords can work as part of a C major key progression. In a lead/melodic context, as we're borrowing them from the parallel minor scale, all we need to do is switch from C major to C natural minor when any of these borrowed chords are used.
Once you've explored the above summary lesson, we can move on to common chords borrowed from other parallel scales.
Mixolydian
The borrowed Mixolydian chords we're going to focus on are highlighted below...
Mixolydian shares six of the major scale's degrees, with the flat seventh degree (♭VII) being the primary distinction. On this degree, harmonised Mixolydian gives us a major seventh (maj7) quality.
Mixolydian also creates a minor seventh chord on the fifth degree (v) - a common substitute for the dominant seventh V.
♭VII (major 7th)
The ♭VII (also called the subtonic) can be thought of as existing a whole step down from the tonic (I). That's the equivalent of two frets, so it's pretty easy to visualise the root positions. For example, in the key of C...
The example below demonstrates this whole step movement between two maj7 chords. A very soulful movement you might recognise from existing songs...
Cmaj7 / Cmaj7 / B♭maj7 / B♭maj7 ( I / I / ♭VII / ♭VII )
With the above root positions, we might play this using the following maj7 shapes...
On that borrowed ♭VII maj7, we can comfortably change from C major to C Mixolydian as our accompanying tonic scale (more on this shortly).
You'll also hear this borrowed maj7 (underlined) in larger major key progressions such as the following examples...
Cmaj7 / Em7 / B♭maj7 / G7sus4 ( I / iii / ♭VII / V )
Cmaj7 / Fmaj7 / Dm7 / B♭maj7 ( I / IV / ii / ♭VII )
Cmaj7 / B♭maj7 / Am7 / Fmaj7 ( I / ♭VII / vi / IV )
In the second example, the ♭VII could be seen as a dominant (V) substitute. For example, instead of ii V I, we might play ii ♭VII I. This is known as a "backdoor" resolution.
v (minor 7th)
Harmonised Mixolydian builds a minor (also minor 7th) chord on its 5th degree (v), giving us another common borrowed chord option. Here's how we might visualise the root positions...
It might seem counter-intuitive to make the dominant (V) a minor chord. However, by using minor on this degree in a major key, we can glimpse at something rather unexpected and beautiful, without losing that major key center. Some examples in C major...
Cmaj7 / Gm7 / Fmaj7 / Fmaj7 ( I / v / IV / IV )
Cmaj7 / Em7 / Gm7 / Fmaj7 ( I / iii / v / IV )
Cmaj7 / Am7 / Gm7 / Gm7 ( I / vi / v / v )
Pattern Changes
When either borrowed Mixolydian chord pops up, we'll want to change from a major to parallel Mixolydian pattern.
Incidentally (and conveniently) there's only one semitone difference between the two scales, on the 7th degree. All we do is lower the 7th of the major scale to get our parallel Mixolydian pattern (♭7)...
Perhaps even more conveniently, if we're using pentatonics, the tonic major pentatonic pattern will cover both the maj7 ♭VII and minor v. Here is C major pentatonic with Mixolydian's 4 and ♭7 greyed out...
Try out different sequences involving borrowed chords, connecting them to their related patterns. I highly recommend using this simple chord track generator as a quick way of creating movements you can play along with.
Lydian
Parallel Lydian connects to a very usable borrowed chord, in the form of its second degree major (also dom7)...
II (dominant 7th)
You'll often hear the diatonic minor ii substituted with a major triad or dominant seventh II. This second degree root is easy enough to visualise - a whole step (two frets) up from the tonic...
Some examples...
Cmaj7 / D7 / Fmaj7 / Fmaj7 ( I / II / IV / IV )
Cmaj7 / Fmaj7 / D7 / G7sus4 ( I / IV / II / V )
Dm7 / G7 / Cmaj7 / D7 ( ii / V / I / II )
Note, on that last example, we changed between major and minor on the same degree (II - ii). This is one option for chord substitution - changing chord quality on a parallel degree.
Pattern Changes
Switching between the parallel major and Lydian simply means raising the 4th of the tonic major scale to a ♯4...
Once again, as we're borrowing from a major mode, we can use major pentatonic on the tonic position to cover the borrowed chord, as a simplified expression (Lydian's ♯4 and 7 greyed out)...
Phrygian
The minor Phrygian mode's flat degrees are especially useful for parallel borrowing. Unique options include the flat second degree major seventh (♭II), flat third degree dominant seventh (♭III) and flat seventh degree minor seventh (♭vii)...
♭II (major 7th)
Only a semitone (one fret) above the tonic, the ♭II is typically used as a V substitute, chromatically falling into the tonic (e.g. instead of ii V I, we might use ii ♭II I)...
But aside from functioning naturally as a pre-tonic chord, it can be used in other contexts, such as a pre-dominant (V), as a more unpredictable, "outside" alternative to other pre-dominant chords such as ii and IV. Let's hear some examples of both...
Cmaj7 / Fmaj7 / Dm7 / D♭maj7 ( I / IV / ii / ♭II )
Cmaj7 / Am7 / D♭maj7 / G7 ( I / vi / ♭II / V )
♭III (dominant 7th)
Distinguished from the natural minor borrowed ♭III, because Phrygian lends us a dominant 7th, as opposed to major 7th ♭III.
The degree can be seen as a minor 3rd interval from the tonic (hence flat three).
This particular chord, as a dominant 7th, is unstable and wants to move somewhere. In the next part we'll see how this type of chord is combined with other non-diatonic, borrowed chords to create a prolonged "outside" movement, still within the overall key. But for now, let's hear how the Phrygian ♭III functions more immediately in an otherwise diatonic context...
Cmaj7 / E♭7 / Dm7 / G7 ( I / ♭III / ii / V )
Cmaj7 / Am7 / E♭7 / G7 ( I / vi / ♭III / V )
♭vii (minor 7th)
Phrygian's minor ♭vii (also called the minor subtonic) is often used as a way of modulating to a new key (e.g. ♭vii becomes the ii of a new tonic).
However, in general it offers a temporary and unpredictable departure from the major key, or as a way of prolonging and re-routing the resolution home.
Cmaj7 / B♭m7 / Am7 / Fmaj7 ( I / ♭vii / vi / IV )
Dm7 / G7 / B♭m7 / Cmaj7 ( ii / V / ♭vii / I )
Pattern Changes
Here we have to lower several degrees from the major scale to get parallel Phrygian (♭2, ♭3, ♭6, ♭7).
However, because of how Phrygian is related to its own parent major scale, we could see C Phrygian (for example) as the same as playing A♭ major (C Phrygian is the 3rd mode of A♭ major).
This ability to see modes as part of a related major scale pattern (and therefore not having to learn an entirely new pattern) is covered in some depth here.
The pentatonic option here is minor, as we're dealing with a minor mode. Change to minor pentatonic on the parallel tonic over any of these borrowed Phrygian chords for something simpler (Phrygian's ♭2 and ♭6 greyed out)...
Dorian
Parallel Dorian is an especially useful reference for the borrowed major 7th ♭III and dominant 7th IV...
♭III (major 7th)
While Phrygian gave us a dominant seventh flat third degree, Dorian naturally creates a major seventh (maj7) on that same lowered third degree. So the only difference here is the chord quality we're borrowing from a different minor mode...
This difference in seventh chord quality might sound subtle at first. But it's a distinction you should train your ears to. Here are some examples of the maj7 being used as the ♭III in a major key...
Cmaj7 / E♭maj7 / Fmaj7 / Fmaj7 ( I / ♭III / IV / IV )
Cmaj7 / Em7 / E♭maj7 / Dm7 ( I / iii / ♭III / ii )
Cmaj7 / Fmaj7 / Am7 / E♭maj7 ( I / IV / vi / ♭III )
IV (dominant 7th)
The IV (fourth degree) chord is naturally (diatonically) a major seventh. However, borrowing Dorian's IV7 (dominant seventh - essentially lowering the major seventh interval) gives us a bluesier quality on this degree. A subtle, non-diatonic change in the natural flow of a major key progression.
Let's hear some examples...
Cmaj7 / F7 / Em7 / Fmaj7 ( I / IV / iii / IV )
Cmaj7 / Dm7 / F7 / G7 ( I / ii / IV / V )
Cmaj7 / Em7 / Am7 / F7 ( I / iii / vi / IV )
Pattern Changes
Here we're switching to parallel Dorian on those borrowed chords. Specifically, we're lowering the 3rd and 7th of major...
Once again, since we're borrowing from a minor mode, the parallel minor pentatonic pattern gives us the simpler "barebones" of what we need to accompany Dorian's borrowed chords (Dorian's 2 and 6 greyed out)...
More on the Pentatonic Option
As we've covered, the familiar pentatonic scales (major and minor) are versatile enough to cover us for the most common borrowed/non-diatonic chords.
The general "rule" is, if we're borrowing from a major mode, play major pentatonic on the tonic position (so, no change if you're already on major pentatonic). If we're borrowing from a minor mode, play minor pentatonic on the tonic position (i.e. change from major to parallel minor).
While this does help to simplify any pattern changes, we are omitting tones from the fuller borrowed pattern (since we're using five vs seven tones). However, pentatonics are a familiar place to begin with learning when to change patterns to accommodate "outside" (non-diatonic) chord changes.
The table below summarises the tonic pentatonic scale we would use for the most common major key borrowed chords in their seventh form (C used as an example)...
Final Notes
We've essentially borrowed chords from five modes of the major scale - Aeolian (natural minor), Mixolydian, Lydian, Phrygian and Dorian.
These five modes are a great place to begin with connecting common, non-diatonic chord changes (i.e. chords that aren't directly harmonised from the tonic major scale) with complementary lead patterns, simply by changing the associated pattern on the tonic position (i.e. parallel).
Hopefully you can hear how these outside chord changes, facilitated and complemented by their naturally related mode, give us more options for developing a more unpredictable chord progression, without completely losing a sense of key center.
Of course, you can play any damn chord you like when it comes to composing a chord sequence! But understanding the melodic implications of those changes, especially when seventh chords are involved, can help you to jump in with the appropriate pattern change for lead accompaniment, while not losing sight of that central tonic position.
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