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Harmonic thinking is a radial model, not a linear list. Keithson visualizes a key centre with multiple independent "strands" of harmonic options radiating from it. When improvising or composing, he draws from these strands simultaneously, not in a fixed order.

The journey from diatonic to sophisticated harmony is about accumulating functional "strands." He started knowing only the seven diatonic chords. Over time, he added secondary dominants, modal interchange, two-fives, tritone substitutions, diminished chords, and five-chord alternatives as separate, learnable systems that all attach to the same key centre.

Non-diatonic chords are justified by their function, not their origin. Every strand is framed around where chords lead: secondary dominants are "the V chord of each of the chords in our key"; diminished chords "function in very much the same way" as dominants; tritone subs work because they "share the same third and seventh."

Thinking in scale degrees and chord types makes everything transposable. For modal interchange, he doesn't memorize specific chords per key. He remembers "chord types over scale degrees" (e.g., "on my flat 2, I've got a major 7"), which gives him "the same options" in any key.

Complex harmony is a tool, not a virtue. He explicitly warns that "a simple or boring chord progression doesn't invalidate a song." Different musical goals (lyrical storytelling, dance hypnotism) may be hindered by complex harmony. "Especially you jazz snobs out there, you know who you are."

Pithy and provocative quotes

"This visual, the key centre with the different strands coming off is quite a good representation really of what's going on in my head when I'm noodling or improvising and sometimes composing."

"For a while I was using some of these options in my playing, but without any real sort of understanding of what they were or how they worked. So a little secondary dominant over here and a bit of modal interchange there, but floating around without any real connection or clarity over why they worked."

"Different songwriters, musicians, composers, they're not all aiming for the same target. They're not all hoping for the same results."

"For some of those results, having complex and interesting or atypical harmony might actually hinder trying to get the result that you want."

"Especially you jazz snobs out there, you know who you are."

Tools, practices, and methodologies

The Key Centre + Strands mental model — A visual framework where a tonic sits at the centre and independent harmonic "strands" (diatonic chords, secondary dominants, modal interchange, etc.) radiate from it. Use it to organize harmonic options and draw from multiple systems simultaneously while staying anchored to one key.

Secondary Dominants — The V chord of any diatonic chord except the tonic. Use them by inserting a dominant seventh chord a fifth above your target chord to create a strong pull toward it. Keithson thinks of these as "five of two," "five of three," etc.

Modal Interchange (Borrowed Chords) — Borrowing chords from any parallel mode or scale that shares the same tonic, then returning to the original key. Keithson limits himself to borrowing from the three parallel minor modes: Dorian, Phrygian, and Aeolian. He memorizes these as chord types over scale degrees (e.g., flat-2 = major 7, flat-3 = major 7, flat-6 = major 7, flat-7 = dominant 7).

Two-Fives (II-Vs) — Preceding any dominant chord with its corresponding II chord. For major destinations, use a minor 7 II chord. For minor destinations, use a half-diminished II chord and an altered dominant V chord. Also includes "backdoor two-fives" and unnamed alternatives that resolve to the IV chord.

Tritone Substitutions — Replacing any dominant seventh chord with a dominant seventh a tritone away, because they share the same third and seventh (inverted). Two applications: (1) swap the diatonic V7 for its tritone sub; (2) swap any secondary dominant for its tritone sub. A practical shortcut: "whatever chord I'm heading to, I can put in a dominant chord a half step above."

Diminished Seventh Chords as Dominant Substitutes — Using fully diminished seventh chords to lead to target chords, exploiting their close relationship to dominant chords (lower any note of a dim7 by a semitone and you get a dominant 7). Practical shortcut: play a diminished chord a half-step below any target chord.

Five Chord Alternatives — A collection of non-diatonic chords that can replace the V7 and still resolve to the tonic, all derived from manipulating a diminished chord built on the raised root of the V chord. Includes: four diminished chords, the backdoor dominant (♭VII7), the tritone sub (♭II7), and several half-diminished/minor 6 options. He rejects any alternative that loses the critical F→E (scale degree 4→3) movement.

Unanswered questions and omissions

How do you choose which strand to use in a given moment? The talk presents a menu of options but offers no decision-making framework. When improvising, how does he decide between a secondary dominant, a tritone sub, or a diminished passing chord to reach the same target?

Voice leading is almost entirely absent. The harmonic options are presented as block chord choices. There's no discussion of how upper voices move, how to voice these chords on piano, or how smooth voice leading might constrain or guide which substitutions work best in practice.

Melody and harmony interaction is never addressed. How do these harmonic substitutions support or clash with a melody? If you're composing a song rather than noodling chord progressions, the melody would heavily constrain which borrowed chords are viable.

The modal interchange section is oddly restricted. He says he "only really borrow[s] chords from my three minor modes" (Dorian, Phrygian, Aeolian), explicitly excluding Lydian, Mixolydian, harmonic minor, and melodic minor. No justification is given for why these are excluded or what "desired effect" the others lack.

Rhythm and harmonic rhythm are ignored. Chord progressions don't exist in rhythmic isolation. How long you sit on a borrowed chord, where it falls in the bar, and how it interacts with meter dramatically affects whether it sounds "interesting" or chaotic.

The "five chord alternatives" derivation is dense and under-explained. The method of raising and lowering individual notes of a diminished chord to generate alternative dominants is presented rapidly. The logic of why some alterations work and others fail (the F→E pull) is mentioned but could easily lose someone without a strong theory background.

No discussion of when not to use these techniques. Beyond the closing caveat about simple progressions being valid, there's no practical guidance on over-harmonization, genre appropriateness, or how to develop taste in applying these tools sparingly.

I thought I'd share with you a little video about how I sort of think about creating interesting chord progressions. If that's something that interests you, then let me tell you about some of the strands that help me formulate my choices. Now let me take you back for a moment to when I was a beginner, when I first started learning and exploring the piano. Now I've always been a chord based player, so at the beginning all I could do was literally just mooch about and explore different chords. In the beginning, all I knew was that each key had a bunch of chords, a chord for each note in the scale.

So each note in the scale had its own chord. And all I was doing was just exploring, moving around those chords, looking to find something that sounded good. So at this point I was just thinking about my key centre and the chords that I had available and I would start to explore. So typically I'd start on my I chord and then think about where could I go from here? So one chord to my six chord to the four, back to the one, to the five, over to the six again, down to the step, down to the four, to the two, to the one.

Nice. So at the beginning, this was the only strand of information that I was really drawing from. It was really all I was aware of at that time, those diatonic chords. But over the years, as my theory knowledge increased and my experience, I learned of a whole bunch of other strands that I could attach to the same key center that would give me a load more harmonic options. So this visual, the key centre with the different strands coming off is quite a good representation really of what's going on in my head when I'm noodling or improvising and sometimes composing.

I've made a free PDF that you can download and explore. But. But let's fly through some of these strands and connections and explain what's happening and then hopefully maybe open up some new connections for you or at least some new ways of thinking about stuff that maybe you're already doing. I'll number these strands for the benefit of talking through them in this video. But really they don't fall into any order of priority for me.

Okay, number one, pretty straightforward. These are all my diatonic chords. We've talked about them already. These are all the chords that exist natively in my key center. Don't think I need to say anymore.

Number two, Secondary dominance. Secondary dominance. None of these chords are diatonic to our key, but they all lead us to chords within our key. Okay, they are the V chord or the dominant chord of each of the chords in our key except our tonic. The dominant of our tonic is already in the key.

It's the V chord. You know this already. So, for example, in the key of C, these are our diatonic chords. And I can use the dominant chord of each of these chords to lead me there. Okay?

So if I wanted to move from my C major to my D minor, the 2 chord, I can use the dominant of that D minor, the 5 chord, 1, 2, 3, 4, 5, to lead me to that chord. So an A dominant seven would lead me to a D minor. Okay, nice. We could think about this as being no in the key of D harmonic minor or D melodic minor. Even the V chord in that key is an A7.

So we're taking the five of D minor. Okay? The same applies for if we want to move TO F major 7 or F major in our key that I can use the V chord of F major. So in the key of F, the V chord would be C7. So although I'm not moving out of the key of C major, I'm using C7 to take me to that F.

Okay? And the same applies for all the other chords. When we're thinking or talking about secondary dominants, we often call them the five of whatever we are heading to. Now, in the case of that A7 that took us to that D minor, that A7 is the five of the D minor. And in the context of the key centre of C major, that D minor is our two chord.

So that meant that the A7 would be our five of two. Okay? So our secondary dominant is always a fifth above wherever we're heading. So depending on what chord we're heading to, it's either going to be the 5 of 2, the 5 of 3, the 5 of 4. You get the picture.

So that first strand on our list is secondary dominance that we can steal these chords to add some non diatonic harmony to our chord progressions. Strand 3 modal interchange or modal mixture or borrowed chords, as far as I'm aware, they all mean the same thing. Definition of modal interchange in a nutshell is borrowing chords from any other key or mode that includes the tonic note of your original key and then returning back to your original key. It's not a modulation. And the most common example of this tends to be borrowing from your parallel natural minor.

So in the key of C major, I would borrow chords from C natural minor. So I could be playing in the key of C major and then I could borrow chords from C Natural minor. Now, I said in my definition that we can borrow from any mode or scale that shares the same tonic. So we've got C major, natural minor, but we could also have C harmonic minor, C Melodic minor. We could have C, Dorian, C, phrygian, C Lydian, etc.

But what I will say is that I don't think all of these are made equal and have the same sort of desired effect. So I'm telling you how I use modal interchange and that I only really borrow chords from my three minor modes of the major scale. So I borrow from Dorian, Phrygian and Aeolian. So Aeolian is the same as our natural minor. So I've lumped together in one strand all the options that I use that already come from those three parallel scales.

Now, it's worth me highlighting that I've written these down on the diagram with numbers rather than chord types. And that's because that's the way that I think about them. And this is an important factor. To think about these as scale degrees and chord types makes it easy for me to access these colors and these options, regardless of what key I'm in, providing you know, your scales and your chord types. So I've been asked before, with modal interchange, how do you remember what your chord options are that are going to sound nice?

And it's just as I've written on the diagram. I remember chord types over scale degrees. So I know I've got. In my head, I've remembered that. On my flat two, obviously we're in the key of C.

On my flat 2, I've got a major 7. On my 2, I've got half diminished. On my flat 3, I've got a major 7 on. On my 4, I've got a minor 7 or minor 6. On my 5, I've got a half diminished, although I don't really use that one very often.

On my flat six, I've got a major seven. On my flat seven, I've got a dominant seven. So I know that these are my options that I can use nicely in that key of C, you know, because I'm thinking about scaled really, So I could think about it in the same way if I was in the key of A flat major, then I know they've got a major seven. On the flat two, which would be. Well, I've got a half diminished on the two.

On the flat three, I've got a major seven. So I've got these same options. I can think about them as scale degrees and chord Types. Okay, onto number four, two fives. Okay, two fives.

Now, some of these are very much connected to our secondary dominants. If you think back to how we thought of those dominant chords as V chords of whatever destination we were heading to, now we can also precede that V chord with the II chord as well. So rather than just playing, for example, the 5 of 4, the C7 of F in the key of C, we can also play the 25 of 4. So in the key of C heading, just before, with our secondary dominance, we just added the C7, which is the 5 of 4 to lead us to the 4 to C, C7 to F. But now we can add the 25 to the 425 of the 4.

So C G minor 7. Okay, so I'm playing the G minor 7, C7 to F because that would be the 2 chord in the key of F. That would be my V chord in the key of F. Make sense? Now that's an example of A major II V, where our destination chord is a major chord.

Now, if our destination chord was a minor chord, then we could use a minor 25 to lead us there. Now, minor 25 works in almost exactly the same way, but the II chord is a half diminished and the V chord is an alter dominant. So if we're in the key of C and we wanted to move to A minor, then to get to A minor, we can use the 2 and the 5 of A, the A minor to take us there. But the 2 this time is going to be A half diminished, so B half diminished. And the 5e is going to be an altered dominant.

So a dominant chord with some alteration. So this has got a third and seventh, got a flat 13 and a sharp nine. So in C. Okay, how nicely does that lead us to that A minor. Now, as well as these Standard well used two 5s, we also have some alternatives that I've sort of picked up over the years.

There's backdoor 25 as a resolution. I've got a tritone sub 2 5. There's a couple that I don't have a name for, but they are two 5s that I know can take me nicely to my four chords. So if I'm in the key of C, I've got this option. Or equally.

So I've got those options attained from a four chord, two. We call these all two fives because of their relationship to each other. Not always because of how they resolve or. Or because of how they're perceived in relationship to the key center. So there's A bunch of two fives that we can think about adding into our chord progressions.

To add some interest, Number five is tritone substitutions. Now, the fundamental idea behind tritone substitutions is that you can swap out any dominant chord for a dominant chord that is a tritone away because they share the same third and seventh, albeit inverted. So what does that mean? A tritone is simply an interval. An interval is the distance between two notes.

So a tritone is the interval of three whole tones. Tritone. Now, in any major key, we only have one diatonic dominant seven chord. That's our V chord. So in the key of C, our V chord is G7.

So we have the option of substituting that G7 for a dominant chord that is a tritone away. So a tritone away from G, whether we go up or down, is D flat. So instead of playing a G7, we could play a D flat seven. Magic. And that's because G7 and D flat 7 share the same third seventh.

Our G7, third and seventh want to pull us to that resolution to the tonic. But those two notes are also in our D flat seven. This is our third and our seventh. So that would be the first use of a tritone substitution that I might introduce to my chord progressions. It's just swapping out that dominant seven chord.

There's another common use of tritone substitutions which is related to what we talked about in secondary dominance. Now, do you remember with secondary dominants, we said that we could pretty much put dominant 7 chord in front of any chord we want because it's going to just help lead us to that chord. Well, if we've put that dominant chord in there, then we could substitute that dominant chord with a dominant chord a tritone away. But tritone substitution of our secondary dominant chord because it will still lead us to that chord. So if we had a simple progression like C, A minor 7, F, just C, I could put a secondary dominant in front of all of those, but then swap out that secondary dominant for the tritone.

An important thing to notice about replacing these dominant chords with tritone subs is that we create these half step movements or semitone movements down to our target chord. So a good way to think about this, and I think probably a really common way of thinking and applying these, is to just think, whatever chord I'm heading to, I can put in a dominant chord a half step above. Okay, we think back to that progression that I just played, that C, A minor, F, C. The tritone subs that got me there were All a half step above where I was going. So I could think, I'm heading to A minor.

All I need to do is play a b flat dominant 7. So a dominant 7 a half step above, then I was going to F. I just need to play a dominant seven half step above. And then I was heading to C and I just played a dominant seven half step above the D flat seven. It's magic.

So that's two ways that I'm integrating these tritone subs. Strand number six, diminished chords. Now I'm talking about diminished seventh chords. So four notes stacked in minor thirds. Diminished chords aren't diatonic to any major key.

So whenever we use them, we're just sort of tiptoeing outside of our key centre. And I'm really using them pretty much in exactly the same way that I use secondary dominant chords. That's because dominant chords and diminished chords are so closely linked. If I take my diminished chord and I lower any of these notes by a semitone, I get a dominant chord. If I take this C and lower it, I've got a B7, B dominant 7 chord.

If I took my E flat and lowered it, it's a D7, my F sharp becomes an F dominant. My A lower it half step, I get an A flat dominant. So because of their similarities, they function in very much the same way. So as an example, earlier on, thinking about secondary dominant chords, we use a five of two to take us to the II chord. So we're in C and we used an A7 to take us to that D minor, the V chord of that II chord.

Now, if we take that V chord, that a 7, and if I was to take the root note and raise it up a semitone, then I've got a diminished chord. This is a diminished chord. Now, every diminished chord is actually 4 diminished chord, depending on what the bass note is. G diminished, B flat diminished, D flat, diminished, E diminished. Okay?

So depending on what bass. And each one of these bass notes I could use, and it would still lead me to that D minor. So I could use the G, I could use the B flat. I could use the D flat or C sharp, I could use the E, Okay? Now I tend to use the leading note that's going to take me to the chord.

So using that C sharp creates this leading note to our destination of that D minor. So another way of thinking about this, like we thought about with our tritone substitutions, I know that I can play diminished chord half step below semitone below any of my target chords. And it's going to help lead me there. So wherever I want to go. If I wanted to go to my A minor, I could use a G sharp diminished.

It's going to lead me there. Okay. If I wanted to go, That's taken me to that G. Okay, so it's a nice little trick as well. Right?

Final one for this video, five chord alternatives. This is a list of non diatonic chords that we can use as alternative to our five chord and will still lead us back to our tonic. So we've covered some of these things already in other strands, but this strand is specifically about this functionality and it does include some things that we've not already covered. This stuff is linked back to that diminished seven chord that we've just talked about. So we take the V chord in our key.

So we're going to stay in C major. So our V chord in C major is G7. If we take that, the root note of our V chord and we move it up a half step, we get a diminished chord. So this is a diminished chord. Remember that?

This is an F diminished and it's an AB diminished and a B diminished and a D diminished. So firstly, the functionality of this is the same as our V chord. So, so we could use an F diminished, an AB diminished, a B diminished and a D diminished to act like a V chord. So we're in the key of C. Okay?

Whichever bass note I put in there, it's still going to have that same functionality. So that's the first thing that we can add to our list is these four different diminished chords are alternatives to our V chord. But this diminished chord can give us more options too. So we know that if we drop that A flat down to the G, we have our tonic. But what if we drop some other notes down?

What if I took my B and dropped it down? What does that give me? Well, that's actually now a B flat seven chord. Okay? So this has enough functionality in this to still move us to that tonic chord.

It's really these two notes that are doing it so I can play. Okay, so this is called a backdoor dominant B flat 7 to my C. Okay, back to our diminished. Instead of moving our B down, what if I move my D down? What does that give me?

Oh, that gives me a D flat 7. Again, that same functionality there is taking me back to my C so I can have something. Okay, so we've got that. So we know that moving that down gives us the G7. This one, B flat, they all work.

Now, the only there's one left for my diminish called moving this down to here. Now, I don't actually use this as an alternative dominant because it doesn't actually satisfy that movement to the tonic. And the reason is, is that we've lost this movement of the. The critical movement here of that F to the E and all our other chords, that G7, our B flat 7, our D flat 7, that F is creating this sort of suspension that's pulling us or this tension that's pulling us to that resolution on the third of our tonic. When we play that E7, that tension and the pull for that resolution isn't there because that E is already in our chord.

So I don't use this as an alternative, but there is more. Instead, take our diminished chord and instead of lowering notes, what if we raise the note? So if we take our A flat and we raise it, we get this B half diminished. Now, this is a diatonic chord. This will lead us to A, I.

This B halt diminished is also a D minor 6 diatonic chord. But we're not here for diatonic chords. So instead of raising our A flat, let's raise our B. What does this give us? So this gives us D half diminished.

So I put the D on the bottom. It's D minus 7 flat 5. And this has the same functionality. This will take us to that tonic, that C as well. So.

How nice does that sound? Okay, now, D half diminished, if we put an F in the bass is an F minor 6. So we could play an F in the bass. Nice. Okay, what if instead of moving our B up to C, what, we move our D up to the E flat.

We get an F half diminished again, it's going to work as well. Nice. And F half diminished is also an a flat minor 6. So the same notes make up an a flat minor 6. So instead of playing an F in the root, I can play an A flat in the root, and it's going to work nicely.

Okay, how nice does that sound? Now, the other note we haven't moved is the F. Again, the reason is because we are. If we move the F up to the here, we lose that movement of the F that wants to pull us back to that C. So again, this isn't so here.

You know, the chords that we get here is an A flat half diminished or it's a B minor 6. But I don't use these as alternatives to my V chord because, again, I'm losing the pull that comes from that F going to the E. So diminished chords giving Us loads of options in terms of alternatives to our dominant chords. Okay, so that's all our strands. Now, I will say that for a while I was using some of these options in my playing, but without any real sort of understanding of what they were or how they worked.

So a little secondary dominant over here and a bit of modal interchange there, but floating around without any real connection or clarity over why they worked or great understanding around these devices and approaches. And so it made it difficult to really explore and exploit them. So spending time learning about these things brought a real clarity and a concrete understanding around where and when I could use these things. By the way, I'd like to say that there's nothing wrong with simple chord progressions. Some of my favorite sounds are simple chords and simple progressions.

And there's something that I like to remind myself of, is that different songwriters, musicians, composers, they're not all aiming for the same target. They're not all hoping for the same results. I do think that most composers and songwriters are looking to produce a response from their listener. For some, that might be to make them feel sad. For some, it might be to make them feel happy, or to tell a story, or to make them want to dance.

Now, for some of those results, having complex and interesting or atypical harmony might actually hinder trying to get the result that you want. I'm sure someone like Leonard Cohen was more concerned with what and how he was communicating through his lyrics than he was about the harmony in his songs. And for someone who's creating EDM dance music, that they're more concerned with creating the hypnotic trance like feeling that their listener can get lost in and dance to. So the point I'm trying to make is that a simple or boring chord progression doesn't invalidate a song or composition. Okay, bear that in mind.

Especially you jazz snobs out there, you know who you are, so there you go. I think there's probably a few other little things that I'm drawing on from time to time when I'm playing, but this gives you a really good glimpse into what's going on in my head when I'm noodling around on the piano. Some of the topics and techniques that I mentioned in this video, I've already made other videos on done a deeper dive, unpack them a bit more, showing how we can use them and utilize them. So if you are interested in learning more about modal interchange, dominant chords, diminished chords, tritone substitutions, modal interchange, then check out some of my other videos. I hope this stuff was interesting.