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Algorithmic songwriting

Try applying algorithm to chord progressions if you feel like you can’t find something new.

This can be really simple or really complex.



Use every third chord in the key.

If you’re in the key of C…


Cmaj       Dmin       Emin      Fmaj       Gmaj       Amin        Bdim


…every third chord would be.


Cmaj      Emin      Gmaj      Bdim       Dmin       Fmaj      Amin       Cmaj


There might be a couple of moves in there that you like, moves you wouldn’t have thought of without using this technique.


A little less simple

Two rules: Use every third chord in the key; make every fourth chord  a seventh chord.


Cmaj     Emin     Gmaj     Bdim7     Dmin      Fmaj     Amin7    Cmaj    Emin     Gmaj7            Bdim      Dmin     Fmaj7      Amin7      Cmaj   etc


Less simple still

Three rules: Use every third chord; every fourth chord is a seventh chord; change key every fifth chord. I’m changing keys by going around the circle of 4ths: Cmaj – Fmaj – Bbmaj – Ebmaj.


Cmaj     Emin     Gmaj     Bdim7    Fmaj      Amin      Cmaj7     Edim     Bbmaj      Dmin7       Fmaj Adim    Ebmaj7   Gmin   Bbmaj    etc.


I find this a bit limiting since it basically just plays the same four-chord progression in a different key. Let’s try making every fifth chord the I chord in the new key and move by thirds in that key. The keys are now Cmaj – Dmin – Emin – Fmaj


Cmaj     Emin     Gmaj     Bdim7     Dmin     Fmaj    Amaj   C#dim7    Emin   Gmaj   Bdom7       Dmin   Fmaj7    Amin7    Cmaj    etc.


These are just off the top of my head. They aren’t designed to be earth-shattering; they’re just for teasing out sounds that you may not have discovered by doing things the way you normally do them.

These ideas can be extended. For example, alternate moving the chords by a third and then by a fourth (i.e. Cmaj to Emin is a third; Emin to Amin is a fourth, etc.)  Notice that I’m staying in the key of C.


Cmaj     Emin      Amin     Cmaj     Fmaj     Amin     Dmin     Fmaj     Bdim      Dmin


With this technique, you get chords repeating themselves more often.

The basic idea here is to think of something to change, and then make that change at a regular time-interval (every third chord; every sixth beat, etc).

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Everyone seems seems to like pedal.

The pedal is that unchanging, drone-like note that gets sustained while other notes or chords change.


Scale-tone triads

This is where scale-tone triads work well. I’m going to use some in the key of A major that I haven’t presented before. I’m using the key of A because I want to use the open 5th string A as the pedal.

Here are the scale-tone triads in the key of A:

scale tone A


Play up and down the scale to get used to the shapes. Notice where it shifts string sets at the 6th chord. Once they feel comfortable, start adding the open A string to them. Try it both strumming or arpeggiating.


Making 7th chords

When you add the pedal (5th string A) to different triads in the A major scale, you get some 7th chords.

  • Adding A to the B minor triad gives you a B minor 7th chord (B, D, F#, A)
  • Adding it to the C# minor triad gives you an A major 7th chord (A, C#, E, G#).
  • The E major chord turns into an E major add 11 chord (E, G#, A, B)
  • The G# diminished chord turns into a G#, B, D, A chord. It makes more sense to spell this B, D, G#, A to produce a B minor 13 chord.


We don’t really hear these chords that way, but knowing this gives you an idea of why the whole thing sounds richer. In the end, though, we tend to hear them like triads sliding around under the pedal rather than 7th chords.


Adding to songs

This is a good technique to use when you want some contrast between verse and chorus, or when you want an interlude going from chorus to verse.

To use this technique in other keys, just tune the 5th or 6th strings to the note you want. For instance, if you want to use the C as a pedal, tune the 6th string down to C. If you want to use the G as a pedal tune the 5th string down to G.

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Incomplete 7th chords

This idea makes 7th chords easier to play, and creates new possibilities. Instead of making them four-note chords, make them three-note chords.


Eliminate a note, of course, but which one? We can’t really get rid of the root or the 7th because they define the sound of the chord. The 3rd also plays an important role in defining a 7th chord’s sound.

But the 5th? We can lose that.


Here’s what you do. Just take any 7th chord, say a G major 7, and build the chord: G, B, D, F#. Now get rid of the 5th, and you’re left with G, B, and F#.

Now the fun part. Find those notes on the neck of the guitar, and build some chords.


Root in the bass

Keep the root in the bass for now. Put the G of the G major 7 chord on the 3rd fret of the low E string. Now find a place for the B and the F#.

You have three practical choices for the B:

  • 2nd fret, A string
  • 4th fret, G string
  • open B string


There are two practical choices for the F#:

  • 4th fret, D string,
  • 2nd fret, high E string.


If you put the B on the A string, the F# can go in any of its two locations. Try both. Which is easier to play? Which sounds better?

Put the B on the G string and, again, the F# can go in any of its two locations. Again, try both. Always ask which is easiest to play and which sounds better.

And finally, the open B. Again, the F# can go in either location.


The root on other strings

Now go through this process with the root on the A string. As before, identify where you can play the other two notes (put them on higher strings than the A), and figure out how many chords you can make.

Then place the root on the D string, and find the other notes. Finally, put the root on the G string.

Remember that, in all these cases, the root is the lowest sounding note.

And make sure that you’re writing down all the chords that you like. The ones you don’t use now, you’ll use later. You keep ideas fresh by making sure that you have materials you like, and by making sure that those materials aren’t all the same.

Some people never use anything but standard, open string chords…


The 3rd in the bass

If you feel like making more chords, put the 3rd in the bass, and then find the root and the 7th on the other strings. So the B (if you’re using the G major 7th chord) goes on the 7th fret of the low E string. Then find the other notes (G and F#) on the other strings. Same process as before.


Other things to try

I know. It never ends.


  • Use the 7th (F#) in the bass, and put the root (G) and the third (B) on the other strings.


  • Do the entire process from the beginning of the post, but get rid of the 3rd instead of the 5th.




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Changing 7th chords

Let’s take the C major 7th chord I talked about in the last post.

Cmaj7 chord

As in my post on ambiguous triads…

…start moving the notes around.


Lots of chords

In some cases when you do this, you get other functional chords (rather than ambiguous ones).

For example, move the 7th of the chord (the note on the E string) down a semitone and you get a C dominant 7 chord.



Move it another semitone down and you get an A minor 7 chord. Suddenly, we’ve changed roots from C to A.



Now, using the A minor 7 chord, move the note on the G string up a semi-tone and you get an A dominant 7.



Move that same note up another semitone and you get an Asus4 chord.

So the work is to simply move your fingers one or two frets up or down on each string, just like you did with triads. The difference is that with 7th chords, you get more material.


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Building 7th chords

The guitar is all about patterns; chords are the most obvious example of this.

Triads are three-note patterns; 7th chords are four-note patterns. If you’re into permutation, you’ll know that there are a lot more four-note patterns.

A quick bit of theory (you may already know this, from me or from some other source):

Triads are built on every other note in a scale. Take the C major scale…


C   D   E   F   G   A   B

1   2   3   4   5   6   7


…and take the first, the third, and the fifth note (C, E, and G ) of the scale to form a C major chord. Add the seventh (B) and you have a C major7 chord.


Knowing the neck

Here’s where knowing the names of the notes on the neck of the guitar helps. If you don’t know them, what I’m about to talk about will hopefully motivate you to learn them. Knowledge equals power.

Here’s a diagram.




Take the notes of the C major7 chord: C E G B. Now let’s see how many shapes those notes make on the neck of the guitar.

I’m going to randomly choose the high E string to place my first note. And I’m going to randomly choose the 7th of the chord (B) to place on that string. The most obvious placement is on the 7th fret. The only other location for that note on the E string is the 19th fret…don’t bother.



It’s kind of like a puzzle. You have one note. You need to find the others. We’’ll make it simple(r) and use adjacent strings – E, B, G, and D. We have the B on the E string; we need the C, E, or G on the B string. Once we have the note for the B string, we’ll move on to the other strings.

What’s possible? The C on the B string is on fret 1 or fret 13. Can you reach either of them while holding down the B? For most people it’s not practical unless you have hands the size of a gorilla’s.

How about the G? No problem. It’s on fret 8 of the B string. And the E is on the 5th fret, so two choices. I’m going to randomly choose the E.

So now you’re holding down the B and the E. You need a C or a G to place on the G string.

You get the idea. Go to the next string (the G) and find a C or a G, and then on to the D string for whatever’s left. Here’s what I wound up with (the numbers below the chart indicate which fingers to use):


Cmaj7 chord


Universe of chords shapes

Then go back and use this process to build a new chord by keeping the B on the E string, and choosing the G (fret 8) on the B string. Then put the C and the E on the remaining strings.

Continue to build new chords. Instead of using the B on the E string, use the C, the E, or the G. Then find the remaining notes on the other strings. Use only adjacent strings like we’ve been doing.


Using non-adjacent strings

Then use non-adjacent strings, say the E, G, D, and A strings. Or B, G, A, and low E strings. You get the picture…

As it turns out, the chord I built above is a common major 7th chord that you could find on any chord chart.

But you wouldn’t find this one built on the E, B, G, and low E strings (the 0 below the chart indicates an open string):


C major7 chord2

Probably because it’s ridiculously hard to grab in the middle of a progression, and only sounds good in particular situations. The point here is to use your knowledge of the neck of the guitar to build stuff you wouldn’t be able to otherwise.


Exploration is good

Some of the things you find will be gold. Some things will need to be explored in different ways (strumming, arpeggiating, etc.) before you figure out how they can be useful. Some things will never be useful.

Now build chords starting on the second note of the scale. That’ll give you D, F, A, and C: a D minor 7 chord.

If it seems like there’s an overwhelming amount to do, that’s because there is. Just keep your eye on what you’re doing in the moment and after awhile, you’ll have a ton of material you can use to make stuff you never would have been able to.

You don’t have to know every possible chord…

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Ambiguous triads

Ambiguous triads sound interesting because their quality (major, minor, etc.) isn’t obvious. Open chords, which I talked about in earlier posts, fall into this category.


Major and minor triads

The main thing that determines chord quality is the nature of the third above the root. It can be either major or minor. The C major triad (for example) has these notes:


  • C E G


The C minor triad has these notes:


  • C Eb G


In these cases C/E is a major third and C/Eb is a minor third (In case you’re not familiar with intervals: count from the first note (C) to the second note (E) – C, D, E – and the number of notes names the interval).


In ambiguous triads there’s no major or minor third above the root. This can lead to interesting sounds.


Scale-tone triads

A good way to work with this idea is to use scale-tone triads. Here are my posts on that.


So take the major shape…


gmaj 3 note in chord box


…and find the third. For this triad, it’s on the G string. Remember, this is the note you need to change for another.

To do that, all you have to do is move the third either higher or lower. Try moving the note as far up or down the string as you can.

Do the same with the minor shape. The third is on the G string in this chord, too.


scale-tone min chord


As you work with this, you’ll notice that the new chord shapes are the same for both major and minor triads. This speaks to the ambiguous nature of these chords. When you get rid of the third of a chord, the chord could be either major or minor. Or neither.

If you want different chord shapes, you can move the other two notes in the triad around, too. This is a nice way of exploring new sounds.


Triads on all string sets

Here’s a link to major and minor triads on all string sets. Diminished, augmented, and suspended triads are on this chart, too, if you want to play around with those.


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