I was watching a video how a guy uses chords from different modes. Let's say I'm in C major, my understanding is that I can borrow any chord from any of the 7 parallel modes to make my chord progression and/or melody more interesting: Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian and Locrian.

But I'm wondering if that ever changes my key? By that I mean, does it modulate the song to a different tonal center? Or as long as I never mess with the I chord then the key is safe? Because I thought I resolve the song with the I chord.

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    Sounds like you can use any chords or any notes to play in any key. You can. – Tim Oct 8 '18 at 18:30
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    Please, please, please stop trying to work from 'rules'. Although a lot of pieces will use maybe only three chords, there is no 'rule' that states other chords, not from that key or its parallel key may not be used. I play pieces in C major that include F# major. They work, but 'don't follow the rules'. Just go with the flow, and stop trying to straightjacket yourself. Please! – Tim Oct 8 '18 at 18:56

It depends on how you define "change the key."

Traditionally, modulation is understood as a change in tonic. If you keep tonic (say, C) the same, you don't modulate. Even if it's between C major and C minor, this is not a modulation, but rather just a change in mode.

So if by "change the key" you mean "modulate," then it's only a modulation if you move to a new tonic. Otherwise, it will be a change in mode. This includes moving from, say, C Ionian to C Lydian.

Modal mixture, meanwhile, is traditionally understood as borrowing scale degrees and/or chord qualities from a parallel mode. Since parallel modes by definition have the same tonic, mode mixture thus will not qualify as a modulation.

Some commenters below seem uncomfortable with the definition of modulation I've given here. Perhaps others on the Internet use "modulation" in a different way, but music theorists are pretty consistent.

Here's Stefan Kostka and Dorothy Payne in Tonal Harmony, 5th edition, page 291:

Because parallel keys share the same tonic, we do not use the term modulation when talking about movement from one key to its parallel. The term change of mode, or mode mixture, is used instead. . . The term modulation is . . . from one tonic to another.

Miguel Roig-Francolí, in his Harmony in Context, page 540:

It should be stressed that modulation implies a change of key center. A change of mode between parallel keys, as between CM and Cm, is not considered a modulation, because the key center does not change (C in both cases).

Countless other authors, including Walter Piston, are still clear that a modulation changes the tonic pitch. In his Harmony, 5th edition, page 221:

The process involved in changing from one tonal center to another is called modulation.

It's certainly possible that others online use "modulation" to mean moving from C major to C minor. But please know that this in contrast to how modulation is traditionally taught in universities and conservatories.

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    @Richard maybe this is incorrect usage, but I've definitely heard people describe something as "modulating to the parallel minor/major". At the end of the day I suppose we're debating semantics not substance, so I suppose it doesn't really matter too much, but I've definitely heard people refer to a strong major/minor change as a "modulation" before. – Some_Guy Oct 8 '18 at 22:18
  • I've read up further about this and I don't think this is just people I've heard using terminology wrong, I'm pretty sure the idea that modulating to the parallel minor/major isn't a modulation is just wrong. I've found plenty of articles, posts and even textbooks that talk about modulating to the parallel minor – Some_Guy Oct 9 '18 at 22:05

Modal mixture is simply one lens through which to understand why certain chords sound good in certain contexts, but it's by no means the only way to look at it.

Music theory seeks to describe why certain musical devices sound good, to try and write music that sounds good by applying some set of rules is getting it completely backwards.

Don't get me wrong, modal mixture is a perfectly valid way to understand a lot of moments of pieces, but it is that; a way to understand why some things sounds good, not a ruled about which chords you "can" use in a certain key, and in some situations it's a useful way to look at it, and in other situations it isn't. What it certainly isn't is a rule for what chords you "can" use in a song.

For example, in common the chord progression:

| C | C | F | Fm6 | C

It's useful to explain borrowing the Fm6 as a "borrowed chord" from the parallel minor, and it sort of helps us why it has the sound of "getting sadder" more or less from the F to the F minor.

On the other hand, you can also look at the voice leading A>Ab>G and say "the F minor sounds good because it is a chromatic passing tone between F and F minor".

And guess what, in this case, they're both right!

On the other hand, if I changed the chord progression slightly:

| C | C7 | F | Fm6 | C

Now, why does that C7 sound good? I could say "it's modal mixture, it's a borrowing from the parallel mixolydian" and I suppose, technically, on paper, it's not wrong. All the notes in that chord are contained in the mixolydian scale, but it doesn't really help us understand what's going on at all.

A better explanation would be that C7 is the V7 chord of F, and so the C7 helps us lead into the F chord nicely and makes the movement a bit stronger, and it prepares us for the chord change that's about to happen. You could consider it a secondary dominant.

And then you take a chord progression like

| C | Am | D7 | G7 | C |

In this example, it has nothing to do with modal mixture. I suppose technically you chord example the D7 as a "lydian borrowing" but really what you have is a classic II V7 I. We use D7 instead of Dm because it prepares the G7 nicely.

Take the famous jazz progression:

| C | A7 | D7 | G7 | C

This one uses the same function as above, but one more level; the A7 is the V of the D7, the D7 is the V7 of the G7, and then you're back home. And this isn't some sort of bizarre esoteric weird sounding "experimental chromatic" progression, it's used everywhere; it's the chords for the chorus of "Oooh, I wanna be like youuu, I wanna walk like you, talk like you..." right?

The point is that there are many different musical devices that help us understand why certain things sound good. In some music, diatonic harmony and modal mixture is a useful thing to think about. In some music, other functional devices are more important (I've just given you 2 really common ones, secondary dominants and voice leading). In other music a bunch of other things are going on. Hell, in some music even the concept of "melody with chords" isn't really the best way to look at it, you have to look at the movement of individual independent voices, or microtonal inflections, or something else entirely!

In the comments you said:

then this site wouldn't be needed. The only guidance would be "meh, just use the chromatic scale to make music!"

In a sense, that's true, to the extent that every note in the chromatic scale, and pretty much every combination of notes (or at least a large large number of them) can be used in a certain key and sound good, given the right context. But that doesn't mean "abandon all theory, just stab at the chromatic scale at random because everything's fine", but it does mean "there is no enforcing a fixed set of allowed and disallowed notes or chords in a key." and it does mean "experiment freely, and see if you find something that sounds good, look in detail at the songs you like and notice what's going on in them, and see if you can understand why things that you like sound good.", and it does mean "learn to play a lot of music so that you can come across new musical features (e.g. chord progressions) and add them to your vocabulary"

If you come across something in a song that you like but you have no idea why it should sound good because it doesn't fit with any of your existing knowledge of harmonic analysis, or you stumble across something while playing around at the piano but you don't understand why it works, but nevertheless you like it, then that's a great time to try and figure out what's going on, and build your knowledge (and that's one of the many things this site is great for).

Also, do be really wary of youtube theorists who look at everything in terms of "scales" and "modes". I'm not saying there's not some valuable material there (there is), but often it's significantly overdone because scales and modes are a nice neat general system logical with clear labels and names, and they can be shoehorned nicely into the youtube infotainment video format.

As a final tip, because I do really want to be helpful and not just seem over critical. If you're noodling at the piano or whatever polyphonic instrument you're playing with, and you want to see if you can find some more "out there" chords that are a little more non-conventional and spice things up, try making chromatic alterations to whatever you're already playing (changing 1 note in a chord by a semitone in either direction and just seeing what comes out), you might stumble on something you like, and then later you'll probably find out why it works. It's one technique among many that can help you to add a bit more non diatonic notes into your music if that's what you're looking for!


"as long as I never mess with the I chord then the key is safe?"

Keep in mind you can have a temporary tonicization of another tonal center which doesn't necessarily result in a key change. How to tell the difference? Relative length of the shift, or better yet check in what key your true cadences occur. Traditionally cadences define keys.

So, you can mess with the I chord for a temporary shift. For example you can put a flat seventh on I (in roman numerals I would become V7/IV) for a change like C7-F. If that move wasn't followed by a cadence in F, probably it wouldn't be considered a key change. You would still be in C major even though the tonic is temporarily acting as a dominant of F.

You could add in the mode mixture idea too and try C7-fm - so that's messing with the tonic and borrowing a chord from the minor mode. That should darken the mood a lot. If you got back to C major quickly and ended the phrase in C major, it probably would not seem to be a key change. (I'm just throwing out some chord change ideas, you might have to play around with such changes to get a phrase that actually works. But I hope it's help illustrate the point.)

  • Devil's advocate - cadences define keys? Sweet home Alabama: plagal or imperfect at the 'end'? – Tim Oct 9 '18 at 7:52
  • @Tim, you mean Lynyrd Skynyrd? When I mention cadences I'm think along the lines of William Caplin. – Michael Curtis Oct 9 '18 at 12:45
  • @Tim, I had to listen to the song again. I guess your point is about the F chord. The song plays D-C-G over and over, I counted 18 times at the beginning, then plays F-C-G. So the first set would be in G. The second set - ostensibly in C - ends on G and could be construed as a half cadence in C. Or, you could recognize the connection to the blues and say it's just a turnaround progression in G. The F becomes a bVII borrowed from the minor - or the mixolydian which is important in blues - and is a substitute for the D or V chord. – Michael Curtis Oct 10 '18 at 5:15

All this is really saying is that you can use any chord you like, and 'theory' will find an excuse for it. If you think I'm being obtuse, find me a chord that COULDN'T be used?

But you're right, randomly selecting chords can just achieve a mess. Maybe we shouldn't be thinking so much of named chords, but of the melodies and intervals that create them. Guitarists in particular tend to think of chords as entities, and of harmony as fully describable by a set of chord symbols. It ain't so!

Notice too that in the video he's not using Modal Interchange to discover exotic chords that fit the sequence. He's choosing nice chords, then using Modal Interchange to justify them. A heck of a lot of chords that DON'T fit in well could still be classed as Modal Interchange.


No. You can 'mess with I' without changing key. I, #Idim7, ii7,V is common.


But I'm wondering if that ever changes my key?

To an extent, that's up to you.

Arguably, the key isn't really part of the essence of a piece of music - Rather, it's a perspective to look at that piece of music from, and to give you a perspective on how the piece works.

Of course, some pieces of music align so well with a certain key that that key seems the only sensible perspective from which to see the piece.

In other cases, it may be helpful to view parts of the piece as being in a different key - or it may be the case that a whole piece is based around an 'ambiguous' chord progression that could be viewed from the perspective of more than one key in its entirety.

BTW your comment...


... would indeed another be valid perspective on many pieces of music - and for some, again, perhaps one you might find useful.

  • I was just thinking how things impact the "tonal center" of a song. I wasn't aware that borrowing chords from a parallel key has no impact on the tonal center. – foreyez Oct 8 '18 at 21:04
  • @foreyez borrowing chords can have an impact on the perceived tonal centre, or the stability of the existing tonal centre. Ask yourself if you perceive it that way! – topo morto Oct 8 '18 at 22:38
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    Your 4th para. I think the vast majority of pieces would be referenced to one key. An exception coming to mind is 'Unforgettable', starts in C, somehow goes to G. I'm sure a lot of symphonic works move very subtly too - but they have plenty of time to do so. – Tim Oct 9 '18 at 7:05
  • @Tim referenced to one key overall, sure, but there can still be numerous moments where another key can be seen as coming into play (anywhere you find a secondary dominant, for example). And though ambiguous chord progressions are the exception, there are still many of them... starting with good old Sweet Home Alabama – topo morto Oct 9 '18 at 7:26
  • Had to play Sweet Home this week, and the band insisted on finishing on D. As some of the original live recordings have (Allman Bros.) But for me, that always sounds like an imperfect cadence rather than the theoretical plagal it is going G>D. – Tim Oct 9 '18 at 7:50

A key will have certain parameters belonging to it. For example, the key of C major uses primarily the 'white keys' found on a piano. No # or b generally.

Once a piece uses accidentals, and keeps using them, it can be said to have changed key. At that point, there is little point in constantly using those accidentals. Just state the new key sig.

By using parallel modes, then, yes, the key will change. By using, for example, C Dorian, Bb and Eb are introduced - both available in the melody and underlying harmony/chords. How can the piece now be construed as being in C major any more?

Yes, of course it's still in C, but C itself isn't a key. If I'm sitting in with a band, and am told the next number's in C, but it turns out to be C minor, I've been misinformed, surely.

So, simple answer to the header - yes!

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    @topomorto - o.k., but if I'm in a band that I've not played with before, knowing a piece is major or minor is pretty critical to what I play! Two rather different sets of notes/chords! – Tim Oct 9 '18 at 8:07

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