A Gentle Introduction to Guitar Chord Theory

jazz comping jazz fundamentals Oct 25, 2020

How to Fully Understand Chord Construction, Triads, Seventh Chords and Extensions

Guitar Chord Theory

Guitar chord theory is the study of chords on the guitar. This includes understanding chord tones, different types of chords (triads vs seventh chords) how chords are derived from scales, and how to find them on the fretboard.

In this article, you will discover guitar chord theory and easily learn about chord construction from simple triads (three-note chords) to slightly more complex and jazzier chords.

In addition, you will find music theory about triads and seventh chords, how to add extensions, chord equivalents, diatonic chords, and finally, a neat theoretical process to understand what extensions are “allowed” on jazz chords.

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One of my goals is to have you realize that you already know thousands of chords, (that is if you already play a little bit). Why? Because any single chord can be put to use in many different contexts, so it’s not a matter of learning more chords, it’s only a matter of finding more USES for the ones you already know!

Furthermore, if you don’t read music (“notes” on the staff) and if you’ve never encountered any music theory in the past, this is a great place to start. So, go slow, read on, and don’t be afraid to ask questions!


Table of Contents


Part 1.................................................Triads and Sevenths

Part 2.................................................Adding Extensions

Part 3.................................................Equivalents

Part 4.................................................Chords from Three Scales

Part 5..................................................The "Chord Extensions Finder" Technique

Definitions........................................A few Generalities, Comments



Guitar Chord Theory

Part 1 — Triads


Triads are built out of three notes.

There are four main types of triads: major, minor, diminished, and augmented. Triads are basically three notes with the interval of a third in-between each of them.

The basic construction of a triad would therefore contain a note, then an empty space, then the note, another space, and finally, the last note.

Each note is the interval of a third, since the note and the space count as one each, it gives us 1, 2, 3 (note, space, note). As a result, there are only two “types” of third intervals where we are left with only four possible combinations of triads.


Intervals: maj3rd then min3rd (as in C-E-G)


Intervals: min3rd then maj3rd (as in C-Eb-G)


Intervals: min3rd and min3rd (as in C-Eb-Gb)


Intervals: maj3rd and maj3rd (as in C-E-G#)


Other Triads

Other types of triads (other than 3rd interval) also exist such as 


SUS4: 1 4 5  &  SUS2: 1 2 5.


These two triads are quite popular in popular songs.

The “SUS” means suspended because the note replacing the “3” in both cases is said to be a suspension of that “3”.

Furthermore, there are a couple of other uncommon oddballs too which we won't bother naming for now (1 3 b5 and 1 b3 #5).

For applications on the fretboard, see this “Triads by String Sets” video:


Guitar Chord Theory and Seventh Chords

First of all, we can apply the same process as above, but this time with four notes stacked together resulting in THREE third intervals. The “space” (the third) can be qualified major or minor, hence creating all the variety found in 7th chords.

We have WAY more combinations available compared to the triads. so hang on to your hats because here are the four main seventh chords used in jazz guitar chord theory which constitute 90% of what’s on sheet music.


Intervals within: (all thirds) maj, min, maj
As in C-E-G-B

MINOR SEVENTH: 1 b3 5 b7
Intervals within: (all thirds) min, maj, min
As in C-Eb-G-Bb

Intervals within: (all thirds) maj, min, min
As in C-E-G-Bb

Intervals within: (all thirds) min, min, maj
As in C-Eb-Gb-Bb — (aka “Half-diminished”)


In guitar chord theory for jazz, the “chord types” above are considered the main 7th chords because they all “live” in the major scale. You’ll find them by stacking thirds on each note of the major scale. It is a good idea for guitarists to learn chords in scale in this manner further explained in this other blog post.


More 7ths

There are a lot of possible combinations, so here are a few more seventh chords.


Intervals within: (all thirds) min, maj, maj
As in C-Eb-G-B

Sometimes spelled 1 b3 b5 6
Intervals within: all minor thirds.
As in C-Eb-Gb-Bbb (or C-Eb-Gb-A)

MAJOR SIXTH: 1 3 5 6
As in C-E-G-A

MINOR SIXTH: 1 b3 5 6
As in C-bE-G-A

MAJOR SEVENTH #5: 1 3 #5 7
Intervals within: (all thirds) maj, maj, min
As in C-E-G#-B



This next one is more appropriately named “maj7th #11” most of the time because it reflects the Lydian mode, and therefore, is a RAISED 4th (and not a LOWERED 5th). 

MAJOR SEVENTH b5: 1 3 b5 7
Usually called maj7(#11)
As in C-E-F#-B


These next chords are further discussed in this post. I recommend reading up a little more guitar chords theory to better understand the relationship between the b5=#4 and of #5=b6. It all makes sense when you know the harmonies found within the scales.


DOMINANT SEVENTH b5: 1 3 b5 b7
Intervals within: (all thirds) maj, min, min
As in C-E-G-Bb
Follow this link for more info on Dom7(b5) (in fact Dom7(#11)

DOMINANT SEVENTH #5: 1 3 #5 b7
As in C-E-G#-Bb
Follow this link for more info on Dom7(#5) (in fact Dom7(b13))


Wanna Play Those on the Guitar?
See the Chord Charts in the “Chords” section of for a complete reference.


That’s all for the most common 7th chords. But wait! Aren’t we seeing a lot of “9” and “13” in guitar chord theory?  How do we create those sounds using theory?  Don't we just add the 9, 11, or 13th on top of the chord?

Yes, but not quite.  We will tackle that very question below in Part 2.


Part 2—Guitar Chord Theory & Adding Extensions

We will now get into some actual processes for building extensions onto basic seventh chords (“jazz chords”).  You are going to find out exactly what those pesky 9's, 11's and 13's are that you keep seeing beside guitar chords.  These symbols are explained below.


Guitar Chord Theory Generalities

  • Triads and Sevenths Chords have been covered in the previous installment of this guitar chord theory article.
  • The major scale still serves as a reference for scale degrees…
    Degrees are raised by a sharp symbol (#) and lowered by the flat symbol (b).
  • When dealing with extensions…Extensions are (usually) identified as notes 9, 11, and 13. It’s important to understand that 9=2, that 11=4 and that 13=6.  Because there are only seven notes on the scale, the note “8” is in fact 1, the note “9” is in fact 2, the note “10”, etc.
  • You can think “linearly”: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 (1)
    As in C D E F G A B C D E F G A B (C)
  • You can think “in thirds”: 1 3 5 7 9 11 13 (1)
    As in C E G B D F A (C)
  • Both ways to think are fine …


Building Extensions in Guitar Chord Theory

So, you’re seeing a chord on a chart that has 13, 11, or 9 (or all of them!) and you’re probably thinking, “Easy! We had 1-3-5-7 so, let’s just add 9-11-13 on top!” … right?! Hold on, we're getting there!

I believe that most of us wouldn’t want to deal with this chord theory mess:

“If I want to build Cm(maj7)(b13) from scratch,
I need the notes … C-Eb-G-B-D-F-Ab … that’s 1-b3-5-7-9-11-b13.”


Yuk! By the time you’re finished computing, the band is already playing the next tune in the book! So the lesson here is; we can’t go “blindly” and just build and build more notes above the root using thirds. Furthermore, on the guitar, we’re stuck with playing six notes at a time maximum! (-:

So, what’s the “guitar chord theory” solution? Well, most of the time, we wind up playing on parts of chords that have extensions. We often omit the root and fifth of each chord to make sure we play the important 3,7,9 etc...  Ideally, we just want to isolate the part of the chord we really need or want.

Meaning, it’s best to understand the principles. Because, that’s why you’re reading the guitar chord theory page, right? So, here’s my suggestion:


A Guitar Chord Theory Trick

First, find the plainest 7th chord that is the closest to your “more complicated” chord that contains extensions. Then, change one or more notes from the basic chord *TO* extensions.

As an example, let’s find a way to play “Cmaj7(13)”. The closest basic seventh chord is “Cmaj7”. Here are some comfortable chord shapes for guitarists as pictured here.

From this point, we are looking to get a “13”. Remember 13=6 so our “easiest” move here is to change the note “5” to a “6” within the original Cmaj7 and hear how it sounds. Question: can you identify the “fifth” in each shape?

Answer: the “5” is the second-lowest note in the two top shapes, and for the two bottom shapes, it’s the highest note. What you want to do is take that note and raise it up to a “6”, that is TWO frets. In short: change the “G” note to an “A” note. I’ll leave you to enjoy discovering the new shapes… some may be comfortable and “playable” and some not! (-:


Let Your Ears do the Walking

Especially relevant, this basic process in guitar chord theory can be generalized by “moves”.  You can take the basic notes 1-3-5-7 and move them up or down to an extension to experiment.  Always let your ears be the final judge. Some stuff you’ll discover WON’T sound good at all!  Here are some legit note moves:

1 to 9
3 to 11
5 to 13
5 to 11
7 to 13

You can also go to b9, #9, #11, b13 (etc.) with this same idea.


However, you may decide (or have to) change more than one note in a basic shape. Simply keep in mind that the root (1) and the fifth (5) are usually the first ones you want to sacrifice, and the 3 and 7 are (mostly) good to keep inside of the new chord. It’s not mandatory, just very common. Also: if you wind up changing 3-4 notes in your original chord, you’ll simply be playing a different chord altogether! It’s good to look at chord equivalents (later in this article) to make your life easier.

Remember: any chord shape you currently know well (even if it’s NOT a basic 7th chord) can be used in this process. Change one or two notes and BINGO, you may find some nice extensions. (For instance, C9 becomes C7(b9) or C7(#9) easily).


Guitar Chord Theory & Getting Extensions by Changing the Voicing

Here’s another practical idea.  Sometimes you cannot just change notes by using 1 to 9, 3 to 11, or 5 to 13.  You have to be clever and re-voice the chord completely.  Consequently, switch two or more note places to create extensions in a common shape resulting in a completely changed way the chord is voiced.

I’ll demonstrate with a favorite example of mine, so grab your guitar.

Our goal is to come up with a Cmaj9 voicing starting from this familiar shape: x3545x. I tried to move the root (1) up to 9 or the 3 down to 9 and I don’t really like the sound, so, I’m gonna “hack my way” to the new extended chord like this: 3 to 9 and 5 to 3.

Therefore, we basically “replace” the 3 that I left out in the first move. This results in the  x3545x becoming an x3243x. Nice eh?! We can use the same guitar chord theory methodology starting from the familiar Cmaj7 in this shape: 8x998x. The same process gives us… (hang on!) … 8x975x. See this:


Try and come up with new shapes using this little guitar chord theory trick above on your own. Self-discovery is very powerful. More powerful in fact than if I simply “gave out” to you all the nice chords with extensions. (-:

Also, check out the article “Don’t Play That Chord” on here for more ideas on transforming some basic 7th chords into beautiful (usable) voicings.


Simplifying your life with Guitar Chord Theory

It’s often easier to check out the jazz guitar chord theory equivalents instead of changing all of the notes within a simple 7th chord,  and that’s exactly what we’ll do below in part 3.


Guitar Chord Theory and Chord Construction 

Part 3 — Equivalents

This part deals exclusively with common chord equivalents. Guitar chord theory becomes really easy once you understand that certain chords are “interchangeable”.  Sometimes, they contain exactly the same notes, and other times they contain another chord’s extensions.



  • You should know- about building triads, basic seventh chords, and *the idea* behind extensions. If not, please read the previous parts of this article.
  • Extensions- In guitar chord theory, we generally label the tones 9, 11, and 13 as extensions.  Alterations (b9, #9, #11, b13, etc.) are also very common, especially on dominant chords.
  • Important- Most recorded jazz over the past 50 years employs chords harmonized to the 9th (minimum). The basic 7th chords are the foundation in guitar chord theory for jazz, but in real life when jazz musicians play, they always use extensions.  As a result, learning jazz chords like this (at least to this extent: 1-3-5-7-9) has become crucial.


What Are Chord Equivalents

Chord equivalents are chords that can easily be interchanged, either in your mind, on the instrument, or literally on the sheet music. Chord equivalents may not have the same “harmonic function”.  However, they may allow you to find some “guitar chord theory shortcuts”, allowing you to find more uses for a single chord.

So, not sure? Okay, here’s an example. You know the Em7 chord, right? What if I told you that from now on, you may play Em7 on your instrument whenever you see a Cmaj7 on sheet music? Does this make sense? NO! Hold the presses, because Em7 and Cmaj7 are completely separate entities in jazz theory.  But, if we take a closer look, we notice that the notes in Em7 are E-G-B-D. Okay. Are these notes “acceptable” to be played over some kind of C major chord?

The notes in Em7 are as follows.

  • E – (it’s the third of C). Check
  • G – (the fifth of C). Check
  • B – (it’s the seventh of C). Check!
  • (So, those are the tones 3, 5, and 7 of C major 7th.)

And what about that “D” note? It’s simply the 9th of C.  Subsequently, by playing an Em7 when you see a Cmaj7 on sheet music, you are simply playing “on extensions” of Cmaj7 (in fact the notes 3-5-7-9) resulting in a Cmaj9 sound. Welcome to guitar chord theory for jazz!

Clearer now? Good! (-:


Guitar Chord Theory Equivalencies

Let's look at two different types of equivalencies for jazz chords:

  •  when two different chord symbols imply the exact same notes and,
  •  when the equivalent is “playing on extensions” of our original chord.
    (The Cmaj9=Em7 example above is of the latter type).

Because I cannot walk you through the same process as above for each and every one of the chord equivalents, I insist that you MUST investigate these on your own. You have to understand what notes are added, left out, and on what extensions is the equivalent placing the emphasis on.

We don’t have enough space here to go into every detail, (and into every key!) so, I’ll simply provide you with a list of common equivalents found in the “real world” of guitar chord theory for jazz. Because once you get familiar with a handful of these interchanging “tricks” as mentioned below, you’ll subsequently find more and more uses for the chords you already know. My goal once again is to have you realize that you know LOTS of chords already; you just have to find more uses for your old stuff. (-:

IMPORTANT: Don’t generalize too much! Consequently, if you’re playing the above example of Em7 when it’s in fact C major 7, it may sound bad IF you don’t respect the registers. Always watch out for the low notes. Most noteworthy, if you play the guitar’s lowest string (E) against a “straight Cmaj7”, it will clash! Therefore, use common sense, listen for that kind of “bad stuff” and let your ear be the final judge.


Equivalents: Same Exact Notes


The very important “maj6 to min7” and “min6 to min7(b5)” are:
C6 = Am7
Cm6 = Am7(b5)

The symmetrical diminished 7th chords are:
B diminished 7th = Ddim7 = Fdim7 = Ab (or G#) dim7

Symmetrical augmented triads…
C aug = E aug = G# augmented


Yup. That’s all there is to know. Once you get this in your ears and fingers plus find out about passing diminished chords (see the Barry Harris Harmonic Method), you’ll find this extremely valuable.

very powerful trick after you nail the “maj6 to min7” relationship, common passing chords, and inversions, is to add extensions to the above! So, much more potential here.


Equivalents: Playing on Extensions

It’s highly recommended that you work each equivalency out for yourself. Explore, and see how it works. As a result, you will find there’s tremendous potential for creativity here!

B dim 7 = G7(b9)
Bm7(b5) = G9
Bbmaj7 = Gm9
Dm7 = G9(sus4)


Fun with triads (in general):

Eb/C = Cm7
D/C = Cmaj7(#11) (lydian)
G/C = Cmaj9
Em/C = Cmaj7

Note: you can take any seventh chord and see it's 3-5-7 degrees as a triad. Subsequently, the same goes with further extensions like 7-9-11 or 9-11-13 which can constitute triads. They’re called upper structure triads. Explore!


More fun with triads (dominant chords only):

Simply a G7sus4 sound with a ninth.

Gives a G7sus4(b9 b13) sound.

Is a G7(b9 b5) sound.

Really cool sound.

Same as above.

Lydian dominant sound. It’s G13(#11).


What’s Next?

We’ll land our two feet firmly on the earth and talk about diatonic chords, the harmony that is already present within a scale in its' natural state. We’ll use our usual suspects: the major, harmonic minor, and melodic minor scales.


Guitar Chord Theory

Part 4 — Diatonic Chords


In this part, you’ll find chord construction for the structure that “lives” within three common scales: major, harmonic minor, and melodic minor. Of course, each scale contains seven notes and hosts one chord on every degree, thus creating 21 chords in this part of the guitar chord theory article.



  • Triad Types: harmonizing the major, melodic minor and harmonic minor scales in triads (3-note chords) will yield the four triad types… Major, minor, diminished, and augmented triads.
  • 7th Chord Types: harmonizing the above three scales up to the 7th (on 4-note chords) will yield only seven different *7th chord types*;
    Maj7, Min7, Dom7, Min7(b5), Maj7(#5), Dim7, Min(maj7) which is to say that some of the possibilities we saw in the first installment of this guitar chord theory article actually exist… BUT NOT in our commonly used scales. *Only* seven types of 7th chords are needed for this foundation.
  • Up to the 13th: To analyze them in regard to what MODES they produce (see scale construction articles) we will build the chords “up to the 13th”  (1 3 5 7 9 11 13) just to see the true identity of each. Consequently, we will have 21 completely independent and unique-sounding 13th chords. Be brave! This all makes a lot of sense when you study chords, arpeggios, and scales at the same time. It will all come together and intuitively blend different elements of guitar chord theory together for you.
  • We’ll look at everything in the key of C for simplicity and demonstration purposes.
  • If you’re unclear as to what these chord types mean, please review the first parts of this article.


Chords From the Major Scale


Little refresher:

the major scale is C D E F G A B or in “formula,” simply 1 2 3 4 5 6 7.

Harmonization in triads:

We simply have major triads on I, IV, and V, minor triads on ii, iii, and vi, and ONE diminished triad on vii.


Triads in C major Scale


In seventh chords: fairly easy once again. We have major7 on I, IV. Minor7 on ii, iii and vi. Dominant7 on V … and our exception once again, the min7(b5) (aka “half-diminished”) on vii. In the key of C:


7th Chords in C Major Scale


Major Scale: Chords “Up to the 13th”

In order to harmonize chords “up to the 13th”, let’s quickly discuss guitar chord theory nomenclature. The problem is often, “How am I going to NAME that chord?!” On this website, we’ll be sticking to an obvious and straight-forward guideline:

  • Write the basic triad name and add the highest non-altered extension degree (either 7, 9, 11, or 13) beside it. Furthermore, write all the altered notes (b5, b9, and so on) in parenthesis beside the chord symbol.

In addition, think about this; every chord harmonized up to the 13th contains seven notes and therefore represents the entire scale. Subsequently, each new chord contains the exact same seven notes BUT starts on a different root. As a result, every 13th chord conveys exactly one mode. You can learn more about this in jazz theory articles about scale construction.

Up to the 13th: Crazy guitar chord theory!


13th Chords in C Major Scale



Let's examine the guitar chord theory behind each formula, chord-by-chord by relating back to each chord’s own root:

C major 13: 1 3 5 7 9 11 13. There are no trouble makers in this one. It contains NO alteration. The “perfect” chord, so to speak. Ionian mode.

D minor 13: 1 b3 5 b7 9 11 13. The only alterations are the third and seventh to make it a minor quality and minor modality. Reflect the Dorian mode.

E minor 11 (b13, b9): 1 b3 5 b7 b9 11 b13. Minor quality, a minor modality with both b9 and b13. This is the most gentle of the weird chords. It conveys the Phrygian mode.

F major 13 (#11): 1 3 5 7 9 #11 13. This is only one note away from the major scale. The #11 makes it sort of “airy” and “dreamy”. It’s the Lydian mode.

G13: 1 3 5 b7 9 11 13. This is the “perfect dominant” so to speak, no alteration. Pure Mixolydian mode.

Am11(b13): 1 b3 5 b7 9 11 b13. Easy to hear “modal” minor scale (also called the natural minor scale). Reflects Aeolian mode.

Bm11(b13, b9, b5): 1 b3 b5 b7 b9 11 b13. Three “ouch” alterations are present; this is very close to being a completely altered chord (11th is the exception). Locrian mode.

Therefore, to further understand 13th chords, please also see the modes explained on the “Scale Construction – Part 3” page…


Guitar Chord Theory and Chords From the Melodic Minor Scale

Most noteworthy, the melodic minor scale is C D Eb F G A B, or in “formula” simply 1 2 b3 4 5 6 7.

Subsequently, with triads, we have minor triads on i and ii. Major triads on IV and V and diminished triads on vi and vii. The exception is an augmented triad on bIII. Especially relevant in the key of C is the following depiction.


Triads in C Melodic Minor Scale


In seventh chords, we interestingly get two dominant chords in a row (IV and V) and then two m7(b5) chords in a row (vi and vii).


7th Chords in C Melodic Minor Scale


Melodic Minor Scale: Chords “Up to the 13th”


13th Chords in C Melodic Minor Scale


First of all, let's examine the guitar chord theory behind each formula, chord-by-chord by relating back to each chord’s own root.

C minor 13 (major 7): 1 b3 5 7 9 11 13. Only the third is flat. The “perfect” minor chord, so to speak. So, that’s melodic minor.

D minor 13 (b9): 1 b3 5 b7 b9 11 13. Another “not so bad” evil chord… only the b9 raises the eyebrows. Could subsequently be called Dorian with a flat 9.

Eb major 13 (#11 #5): 1 3 #5 7 9 #11 13. This has a very “hyper” sound for a chord because of its sharps. It’s sometimes referred to as Lydian Augmented.

F13 (#11): 1 3 5 b7 9 #11 13. Simply put, a “perfect” dominant with only one alteration. Sometimes called Lydian Dominant…

G11(b13): 1 3 5 b7 9 11 b13. Another very pure dominant with just one alteration. Often called Mixolydian flat 13…

Am11(b13, b5): 1 b3 b5 b7 9 11 b13. A chord is often used in outlining the “II” chord in a minor II-V-I situation. Sometimes called Aeolian b13 OR Locrian with a natural 9th.

Bm7(b13,b11,b9,b5): 1 b3 b5 b7 b9 b11 b13. This is starting to look really bad. Most often used as a dominant and called “the altered scale”. Conveys the super Locrian mode.


To further understand 13th chords, please also see, the modes explained on the “Scale Construction – Part 4” page…


Guitar Chord Theory and Chords From the Harmonic Minor Scale

Especially relevant: the harmonic minor scale is C D Eb F G Ab B or in “formula,” simply 1 2 b3 4 5 b6 7.

In triads: We have minor triads on i and iv. Major triads on V and bVI. Diminished triads on ii and vii and still the augmented triad on bIII. In the key of C:


Triads in C Harmonic Minor Scale


In seventh chords: This is getting crazy because every chord is of a different type. Examine, study and reflect. In the key of C:


7th Chords in C Harmonic Minor Scale


Harmonic Minor Scale: Chords “Up to the 13th”

Up to the 13th: Some more crazy guitar chord theory!



13th Chords in C Harmonic Minor Scale


So, let's examine the guitar chord theory behind each formula for the harmonic minor scale, chord-by-chord by relating back to each chord’s own root:

C minor 11 (maj7)(b13): 1 b3 5 7 9 11 b13. Only the third and sixth are flat. That’s harmonic minor. Not often used as a chord.

D minor 13 (b9 b5): 1 b3 b5 b7 b9 11 13. Could be called “Dorian b9 b5” or even “Locrian Natural 13.” Doesn’t make much sense.

Eb major 13 (#5): 1 3 #5 7 9 11 13. The only chord in this scale that gets “LESS crazy” from the alterations. Often used (remember the last chord in “James Bond Theme”?)

Fm13 (#11): 1 b3 5 b7 9 #11 13. Hard to describe. Can be referred to as “Dorian #11” but doesn’t make much sense.

G11(b13 b9): 1 3 5 b7 b9 11 b13. Used all the time both as a chord and scale. “Harmonic Minor of Destination” or often called Mixolydian flat 13 flat 9…

Abmaj13(#11, #9): 1 3 5 7 #9 #11 13. Just the thought of a #9 on a major chord makes me shiver! Nevertheless, this is employed in jazz for the past 30 years. We could say “Lydian #9”.

B WHAT?!?: 1 b3 b5 bb7 b9 b11 b13. This chord is hard to name because every note is altered AND the 7th is doubly altered! Thinking of the bb7 as a 6 (enharmonic relationship) we could call this Bm6(b13 b11 b9 b5) … but I don’t think there’s hope! (-:

To further understand 13th chords, please also see the modes explained on the “Scale Construction – Part 4” page…



Please do not worry if you cannot grasp everything at once. Learning guitar chord theory for jazz (and learning with your ears) is a lifelong endeavor. Simply make sure you come back here often. (-;

For now, see if you can play the basic 7th chords in drop-2 and drop-3 voicings in those three scales. You can also check out how to approach those “crazy guitar chord theory” 13ths “as complete arpeggios” in this article and how to tame them down to be simple triads and seventh chord arpeggios in this article.


“Chord Extensions Finder” Technique

Part 5 — Guitar Chord Theory and Extensions


This chord extensions primer can help you visualize both the components of chords AND scales.  Extensions are both vertical and horizontal!

Note the flat 9 in the following scale. Continue reading to find out why and how it is a flat 9.


  • What is a “b9”?  Answer: the interval consists of the distance of 13 half-steps between two notes. For instance: E to F (the latter being an octave higher). In fact, you can think of the “b9” as a minor second with octave displacement: a half-step for which the highest note is “up the octave”.  Try it on your guitar.  Each fret is a half-step.
  • Extensions:  Extensions are considered the tones 9, 11, and 13 (including alterations of them, such as #9, b13, and so on.)
  • Scales and Modes: The process below can be applied to any scale or mode, but it’s best to start with all the chords in the major, melodic minor, and harmonic minor scales first.


Chord Extensions: Why This Process?

The process described in the following paragraphs will allow you to find what extensions “are good” (viable and good sounding) and which extensions you cannot use most of the time. There’s only one “rule” in guitar chord theory for this and it’s the “b9 rule”. In short: we want to avoid having the interval of a b9 within a chord.

A “b9” is created by adding one or many extensions!

Subsequently, the rule is:

if an extension you've made creates a b9, DON’T use it. The only exception is between the root and the b9 of dominant chords.)

Finally, this has to be done “case by case”. We cannot assume that all minor 7th chords will “accept” the same extensions. We have to think in terms of function. For instance: “In a progression, is this min7 chord functioning as IIm7 or VIm7 ?” The answer will give you what SCALE is typically used for that function and also the origins of the chord at hand, and this allows you to add 9, 11 and 13 on top.

Depending on the scale at issue, some extensions will “create” our public enemy #1, the b9 interval.

As a result of this guitar chord theory discussion on extensions, you will understand exactly how to add these extensions to a chord, and know the what, where, and how as well.

Truth be told after you do this once for a certain chord function, you’re set! You’ll find the ones that are commonplace and all the other ones that are usually avoided.

Have fun! Guitar chord theory rules!


Let’s do it!

Ok, so here it is! It’s going to be a bit more involved on the jazz theory side of building extensions so you’ll need a piece of paper and some time to puzzle things out for yourself.

  1. Write a scale down (two octaves);
  2. Define the 7th chord;
  3. Define the 9, 11, and 13 extensions;
  4. Determine which of the three above are available according to the “b9 Rule”;
  5. Rinse and repeat.

The last step refers to using the next mode available. For example, if you just found the available extensions on a C major chord, why not use the same process from D to D and find the available extensions on the IIm7 (Dm7) chord in the key of C major, etc.


An Example: the C major 7th chord in the key of C major

To get you started in guitar chord theory extensions, here’s an obvious example to demonstrate the “b9 rule” and the whole process involved in finding what chord extensions are available on a Cmaj7 chord in the key of C major.


Step 1: Write the Scale Down


Step 2: Define the 7th Chord


Step 3: Write 9-11-13


Step 4: Apply the “b9 Rule”


Therefore, this guitar chord theory process is telling us that chord extensions on C major 7th (acting like an I chord) are typically the 9th and the 13th (both natural). The natural 11th is usually avoided because the b9 would be created with the 3rd. Voila! as a result, “Cmaj9” or “Cmaj9(add 13)” or “C6/9” are commonplace while Cmaj11 is almost never encountered.

If you’re even mildly interested in this idea, I encourage you (very much!) to take 15 minutes and do this starting from all the notes in C major. You’ll be finding the “right” extensions for Cmaj7, Dm7, Em7, Fmaj7, G7, Am7, and Bm7(b5) in a C major tonality. It’s worth your while, I promise.

Furthermore, replicate the exact same process with C melodic and C harmonic minor … you’ll find funny jazz chord extensions in funny places! (-:

Don’t forget to use the degree numbers. For instance, Dm7 in C major (Dorian mode) is 1 b3 5 b7 9 11 13, and always use proper degrees whereby you’ll find beautiful extensions such as #11 and b13!


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  • “Chord” means that all the notes are sounded together, at the same time.
  • The major scale serves as a reference when identifying chords by scale degrees… and that’s exactly what numbers mean in this article.  For instance, 1 3 5 means to play the first, third, and fifth notes of the major scale. This goes for any chord found in this article. Degrees are raised by a sharp symbol (#) and lowered by the flat symbol (b).
  • Chords are built in intervals of ascending THIRDS (2 or more).  This works 99% of the time. A third is a space (called “interval”) between two non-consecutive scale notes, up or down. For instance, C-E is an ascending third (say “C D E” in your mind). The same thing works descending: C-A is a third (say “C B A” in your mind) but with chords. Consequently, we won’t deal with descending intervals.
  • So, a chord will usually contain ODD numbers like this 1 3 5 7 9 11 13, up to a maximum of 7 notes (on this website at least).


Now that you know a bit about guitar chords theory, why not dive into CHORD SUBSTITUTIONS and learn how to spice up your comping?

Ever wonder how jazz guitarists get all these fresh and different sounds out of their comping and solo guitar playing? Well, a lot of that has to do with the use of chord substitutions. In our guide, we’ll go over the basics and even some more sophisticated techniques you can use to spice up your harmonic content!


For intermediate guitarists ready to "crack the code" in jazz


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