Guitar Chord Theory [Understanding Chords On Guitar]

Interested in learning how chords are built, rather than just relying on remembering chord shapes? This introductory guide to guitar chord theory describes how chords are constructed from scales, how chords are named, the difference between chord qualities such as major and minor, and a whole lot more. So if you’ve ever wanted to understand the theory behind chords, stay tuned!

Table of Contents

What is guitar chord theory?

Guitar chord theory is a subset of music theory involving the study of chord construction from scales and the quality (major, minor, etc.) and type (triads, 7th chords, extended chords) that can be formed based on the intervals (distance between notes) and number of notes used to build them.

What are chords?

Any combination of three or more different notes played at the same time, usually in support of a melody.

Chord charts

Chord charts demonstrate how a guitar chord should be played. The following chart shows ‘A major’ in the open position.

The chart is an image of the fretboard. The thicker bass strings are on the left and the treble strings to the right. The vertical lines represent the strings. The horizontal lines represent the frets. The dots represent the finger placement on the fretboard.

The ‘X’ above the first fret indicates the string is not to be played, while the ‘O’ indicates the string is to be played but isn’t fretted, or in other words, is an open string.

I’ve written a complete guide to reading chord charts which goes into more depth here.

How are chords named?

Chords are named based on the root note and quality of the chord. For instance, F major takes its name due to the root note being ‘F’ and being of ‘major’ quality. Below is an example of a D major.

Root Notes

The root note defines the chord. For example, D is the root note of all D chords (e.g. major, minor, augmented, suspended, etc.).

C is the root note of all C chords and so on. The root note is the first note of the corresponding scale e.g. the C major scale.

*It helps to have a basic understanding of guitar scale theory, which you can read more about here.

In most cases (but not always) the root note is the first and lowest-pitched note. Chords that consist of the root note being the lowest pitched note are called ‘root position chords’.

For instance, when playing an open position D major chord, the lowest note is the open D string (4th string) as the A and low E strings are not played (as indicated by the ‘X’.

For the majority of open-position chords, the root note will be a note played on either the low E, A, or D strings.

Repeat Notes

Notes are often repeated in chords. For instance, the following are both C major as C major is built from C (root), E, and G.

While the first shape includes just three strings, the second example includes all 6 strings, however as only C, E, and G are used to form a C major chord, in the second example, the notes are repeated.

Chord shapes that include repeated notes often do so to make the chord easier to play (consider the muted strings in the first example) and also tend to sound richer due to incorporating more strings.

The second example is an inversion of C major, as the lowest note is G.

What are Chord Inversions? Chord inversions are variations of standard chords where the lowest note is not the root note of the chord. In a chord inversion, a note other than the root becomes the lowest note, changing the chord’s voicing and sound. Chord inversions are used to create smoother transitions between chords, and add variety to chord progressions.

Chord qualities

Regardless of your experience with music, you will have heard the terms ‘major’ and ‘minor’, which are a way of describing a chord’s ‘quality’ which describes its distinctive sound or flavour.

For example, major chords are described as sounding happy. Minor chords are described as melancholy and sombre.

Chords are not restricted to only major, or minor, however. The table below shows the four most common chord qualities.

Quality	Suffix	Description
Major	Maj	Happy, simple, resolved
Minor	min	Dark, serious
Diminished	dim	Tense, dissonant
Augmented	aug	Suspenseful, unnatural

The chords above are triads, which we’ll discuss in more detail in the next section. Other less common qualities include, but are not restricted to:

Quality	Suffix
Suspended fourth	sus4, (sus)
Suspended second	sus2, (sus)
Added ninth	add9
Minor added ninth	m(add9)
Fifth	5, (no3)
Sixth	6
Minor sixth	M6m (-6)
Sixth, added ninth	6/9
Minor sixth, added ninth	m6/9
Seventh	7, (dom7)
Minor seventh	m7, min7, -7
Diminished seventh	dim7, dim
Seventh, suspended fourth	7sus4, 7sus
Minor, major seventh	m(maj7), m(+7)
Major seventh, flat fifth	maj7♭5, maj7(-5)
Minor seventh, flat fifth	m7♭5, m7(-5)
Seventh, sharp fifth	+7, 7(♯5)
Seventh, flat fifth	7♭5, 7(-5)
Seventh, flat ninth	7♭9, 7(-9)
Seventh sharp ninth	7♯9, 7(♯9)
Ninth	9
Major ninth	maj9, M9
Minor ninth	m9, min9
Eleventh	11
Minor eleventh	m11, min11
Thirteenth	13

Types of chords

Triads, sevenths, and extended chords

Chords can be categorized into groups based on the number of notes they are constructed from and include triads, seventh, and extended chords.

Triads

A triad is a set of three notes, typically consisting of a root (the first note from the corresponding scale), a third (the third note from the major scale), and a fifth (the fifth note from the major scale).

Triads are the most basic type of chord in Western music, serving as the building blocks for more complex harmonies.

Augmented triads are similar to major triads, utilizing the root and major third (3rd scale degree of the major scale), however, the 5th note of the scale is, as the name implies augmented e.g. raised half a step (semitone).

A diminished chord (also a triad) is similar to a minor chord e.g. it utilizes the root, minor third (third scale degree of the minor scale), and a diminished 5th e.g. lowered half a step (semitone).

If this is confusing, don’t worry.

We’ll discuss intervals (the distances between two notes, measured in terms of pitch and defined by the number of semitones they encompass) shortly but for now, consider chords as triads, with seventh and extended chords having additional notes added from their corresponding scale.

Seventh chords

A seventh chord (7th chord) is essentially a triad that includes a 4th note. The dominant 7th is the most common on guitar and is simply a major triad with a minor 7th interval added. This combination of major and minor intervals tends to sound bluesy.

This makes sense if you consider that blues tend to utilize the notes of the minor scale over major chords and it is often the tension between major and minor that we associate with a ‘bluesy’ sound.

Again, if this doesn’t make sense right now, don’t worry, this will become much clearer as we go along. You can also read my guide to 7th chords here if you would like to learn more.

What are Scale Degrees?
Scale degrees are specific positions or steps within a musical scale, each corresponding to a note and denoted by a numerical value. These degrees help in building chords relative to the root note of the scale.

For example, the C major scale’s 3rd scale degree is E.

Scale Degree	1	2	3	4	5	6	7
Notes	C	D	E	F	G	A	B

We can build a C major chord using the 1st, 3rd, and 5th scale degrees from the major scale.

Extended chords

Like 7th chords, extended chords are constructed from more than three notes, with any additional notes beyond the basic triad extending beyond the 7th scale degree. This means they include notes from the next highest octave. Examples include 9th, 11th, and 13th chords.

An octave, is an interval that represents the distance between two notes of the same pitch, with one being half or double the frequency of the other. For instance, your open E string is technically the same note as the 12th fret of your E string but twice the frequency.

You can read more here about why we hear notes an octave apart and recognize them as being musically equivalent here.

What about two-note chords?
You may have heard guitarists refer to two-note ‘power chords’. These include the root and fifth scale degree only. They are neither major nor minor in quality as they do not contain a third scale degree which would otherwise determine a chord to be major or minor.

For now, it’s helpful to understand that any notes played together are considered harmony (the combination of one or more notes) but for the notes to be a chord by definition they must contain at least three different notes.

How chords are built

The chord scale relationship

Chords are built from scales. They go hand in hand when it comes to creating rhythm and melody. For example, playing notes from a corresponding scale e.g. the E minor scale over an E minor chord will sound musical, or in key.

Below are the notes for the C, E, and G major scales and the notes that form the corresponding major chord. See if you notice a pattern.

Scales	Chords
C Major Scale C – D – E -F – G – A – B	C Major Chord C – E- G
E Major Scale E – F♯ – G♯ – A – B – C♯ – D♯	E Major Chord E – G♯ – B
G Major Scale G – A – B – C – D – E – F♯	G Major Chord G – B – D

The difference between scales and chords is how they are constructed. For example, scales utilize step patterns that determine their quality e.g. major, minor, etc.

Step patterns include whole (W) and half (H) steps. Whole steps represent 2 semitones (2 frets on the fretboard), while a half step represents a semitone or a single fret.

The major scale is derived from the chromatic scale (all notes included in Western music) using the following step pattern:

Major scale step pattern
W – W – H – W – W – W – H

Chords can be constructed from scales using intervals (more on this shortly) or a formula based on the notes of the major scale.

Method 1: Scale Degree formulas and the major scale

We can build chords using formulas based on the major scale. For example, the scale degree formula for major chords is:

Major scale formula
1 – 3 – 5

This means we take the first, 3rd, and 5th notes (scale degrees) from the major scale to build a major chord. Each note in a chord is known as a chord tone. The tonic (starting note) of the scale determines the value of the chord. For example, the A major scale consists of the following notes:

The A Major scale
A – B – C♯ – D – E – F♯ – G♯

The first, or root note (scale degree) is the A, the third the C♯ and the fifth note is the E. This means the individual notes (scale tones or scale degrees) that make up A major are A, C♯ , and E.

A Major Chord - Derived from A Major Scale

Minor chords, on the other hand, may also reference the major scale but instead use the formula: 1, ♭3, and 5.

This means the third scale degree is flattened by a half step. This is useful in a practical sense as it means you can make any major into a minor chord by flattening the third a half step (semitone), which is simply one fret on the fretboard. All chords constructed using scale degrees reference the major scale in this way.

It’s also true that if you constructed a minor chord from the starting point of its corresponding natural minor scale, you would utilize the 1, 3, and 5 scale degrees of the minor scale, as seen in the example below:

The A minor scale
A – B – C – D – E – F – G

Based on this, the chord notes required to construct an A minor chord are A, C, and E.

Common chord formulas

Below is a list containing the most common scale degree formulas. Using the formulas below will allow you to construct your own chord voicings anywhere on the fretboard.

Type	Formula
Major	1 – 3- 5
Minor	1 – ♭3 – 5
Diminished	1 – ♭3 – ♭5
Augmented	1 – 3 – ♯5
Suspended fourth	1 – 4 – 5
Added ninth	1 – 3 – 5 – 9
Minor added ninth	1 – ♭3 – 5 – 9
Fifth (partial or power chord)	1 – 5
Sixth	1 – 3 – 5 – 6
Minor sixth	1 – ♭3 – 5 – 6
Sixth, added ninth	1 – 3 – 5 – 6 – 9
Minor sixth, added ninth	1 – ♭3 – 5 – 6 – 9
Seventh	1 – 3 – 5 – ♭7
Minor seventh	1 – ♭3 – 5- ♭7
Diminished seventh	1-♭3-♭5-6
Seventh, suspended fourth	1 – 4 – 5 – ♭7
Minor, major seventh	1 – ♭3 – 5 – 7
Major seventh, flat fifth	1 – 3 -♭5 – 7
Minor seventh, flat fifth	1 – ♭3 -♭5 – ♭7
Seventh, sharp fifth	1 – 3 – ♯5 – ♭7
Seventh, flat fifth	1 – 3 – ♭5 – ♭7
Seventh, flat ninth	1 – 3 – 5 – ♭7 – ♭9
Seventh sharp ninth	1 – 3 – 5 – ♭7 – ♯9
Ninth	1 – 3 – 5 – ♭7 – 9
Major ninth	1 – 3 – 5 – 7 – 9
Minor ninth	1 – ♭3 – 5 – ♭7 – 9
Eleventh	1 – (3) – 5- ♭7 – (9 )- 11 * (3) and (9) are optional
Minor eleventh	1 -♭3 – 5 -♭7 – (9) – 11 * (9) is optional
Thirteenth	1-3-5-b7-(9)-(11)-13 * (9) and (11) are optional

What’s the deal with suspended chords?
You might notice suspended chords (along with power chords) are the only chords that do not include the third scale degree. Suspended chords replace the third with a fourth (sus4), or a second (sus2) scale degree. Because of this they are neither major or minor as the third is not included.

What are diminished chords?
A diminished chord is simply a minor chord with a flattened fifth scale degree. There are three types of diminished chords (as seen in the chart above) diminished triads, half-diminished, and diminished 7th chords.

Method 2: Using intervals

We can also construct chords from scales using intervals. Intervals can be ‘harmonic’ e.g. played together, as is the case with chords, or ‘melodic’ meaning the notes are played sequentially. Before we can build chords using intervals, first we need to discuss the master of all scales, the chromatic scale.

The chromatic scale

There are 12 notes in Western music. These 12 notes make up the chromatic scale. This means every scale (along with every note) comes from the chromatic scale, and as a result, is helpful to think of the chromatic scale as the ‘master scale’.

Whole steps and half steps (whole tones and semitones)

The notes in the chromatic scale are separated by half steps. A half step is a distance between two adjacent notes e.g. A to A♯ is one-half step (1 fret on the guitar), equal to a minor second interval (more on this shortly). While a whole step (2 frets on the guitar) is twice this distance e.g. A – B.

This tends to make more sense when considering the layout of a piano. The first arrow indicates a half step, and the second arrow shows a full step between the D# and F.

The white keys are whole notes e.g. C, D, E, F, G, A, and B. The black keys in between are sharps or flats e.g. C♯, D♯, F♯, G♯, and A♯

When you see notes, denoted with a sharp symbol(#) or flat symbol (♭) but appear to be of equal pitch, they are referred to as enharmonic equivalents, meaning they are of the same note value e.g. a C♯ is the musical equivalent of a D♭.

Only 5 of the 7 notes have sharps or flats. This is why the piano does not feature black keys between each white key, which as it turns out is a good thing as it would be difficult to navigate the keyboard otherwise.

Why are intervals important?

Half and whole steps are a type of interval e.g. the distance between notes. Half and whole steps are fine for discussing smaller intervals, but when the distance between notes is more than a whole note we can use additional terminology.

If we want to understand how major chords are constructed without referencing the major scale it’s more good practice to learn the intervals rather than the notes themselves.

The intervals for all major chords are the first (root), major third (four half notes from the root), and perfect fifth (7 half notes) taken from the chromatic scale. In the case of minor chords, we simply change the major third to a minor third (3 half notes).

This means you only need to know the intervals of each chord type rather than the individual notes, making it easier to construct chords or adapt a major chord to a minor by simply flattening the major third to a minor third. This shouldn’t be confused with scale degrees, which are based on the major scale.

The difference between using scale degrees and intervals

Scale degrees reference the major scale and are relative to the root note, meaning the root is counted as 1 because it is the first scale degree and the ascending scale degrees from the root (2, 3, 4, 5, 6, 7) define the position of the note in the scale relative to the root note.

Intervals on the other hand define the distance between any two notes (if discussing the distance between two notes of a scale we use the term diatonic interval). The interval number refers to the number of whole notes or letters between the two notes.

As we can see in the table below the distance between A and C spans three letter names (A, B, C) in the musical alphabet, so this interval is a third. To determine the interval’s ‘quality‘ we need to establish how many notes this includes (A, A#, B, C) four notes, meaning the interval is a major third. If it was three notes it would be a minor third.

1	2	3	4
A	A#	B	C

How intervals relate to each other

There are 5 categories of intervals:

Perfect: 5th, 4th, unison and octaves
Major: 2nd, 3rd, 6th, 7th
Minor: 2nd, 3rd, 6th, 7th
Augmented: Half step added to a perfect or major interval
Diminished: Half step reduced from a perfect or major interval

These categories relate to one another. For example, a major interval when reduced by one step becomes a minor interval.

Distance Between Frets/Notes	Interval Name
3	Minor Third
4	Major Third

Alternatively, If we lower a perfect interval by one step, the interval becomes a diminished interval, and a major or perfect interval if raised a half step becomes an augmented interval.

Different intervals have different names. Below is a table listing the 12 intervals, the distance between the notes, and the interval name.

Distance Between Frets/Notes	Interval Name
0	Unison
1	Minor 2nd
2	Major 2nd (Diminished third)
3	Minor 3rd (Augmented second)
4	Major 3rd (Diminished fourth)
5	Perfect 4th (Augmented third)
6	Tri-tone (Diminished fifth)
7	Perfect 5th (Diminished sixth)
8	Minor 6th (Augmented fifth)
9	Major 6th (Diminished seventh)
10	Minor 7th (Augmented sixth)
11	Major 7th
12	Perfect Octave

How intervals are named

Intervals are named by their interval type and their interval number e.g.

Unison
Seconds
Thirds
Fourths
Fifths
Sixths
Sevenths
Octaves

Perfect intervals (P)

Intervals that are either unison, 4th, 5th or a whole octave are known as perfect intervals. They remain the same whether inverted. An inverted interval is an interval that has been turned upside down e.g. the starting note becomes the final note and vice versa.

Non-perfect intervals

Non-perfect intervals are either major or minor and include the second, third, sixth, and seventh.

Augmented intervals (A)

Augmented intervals are perfect or major intervals raised by half a step.

Diminished intervals (d)

Diminished intervals are perfect or minor intervals lowered by half a step.

How major chords are built using intervals

As we know, major chords consist of the root note or first, the 3rd (the 3rd is major unless otherwise indicated), and the 5th (perfect fifth) intervals.

If we build an A major chord, starting on the A (the tonic note of the A major scale) we get the following notes (highlighted below):

A – A# – B – C – C♯ – D – D#- E – F – F# – G – G#

The first note is the A.
A major third from the root note (4 half steps) is the C♯
The perfect fifth from the root (7 half steps) is the E

This means A Major consists of the notes A, C♯ , and E.

Qualities and intervals

Below is a list showing the 4 triads we listed at the beginning of this article and their respective intervals.

Quality	Interval Formula
Major	Root – major third (M3) – perfect fifth (P5)
Minor	Root – minor third (m3) – perfect fifth (P5)
Diminished	Root – minor third (m3) – diminished fifth (dim5)
Augmented	Root – major third (M3) – augmented fifth (Aug5)

Chord Progressions

Now that we have a foundational understanding of how chords are built, the different types and qualities of chords, and their relationship to scales, you might be wondering where to from here.

I’d recommend learning about keys and why specific chords and notes sound right together.

FAQ

What is a dominant chord?

This can be confusing as the term ‘dominant’ refers to two different things musically. If discussing chord function (the relationship and movement between chords) dominant chords are chords built on the 5th scale degree.

If we look at a C Major scale for example:
C – D – E – F – G – A – B

The dominant chord in the key of C would therefore be G, as this is the 5th scale degree of the C Major scale, and therefore the root note of the dominant chord. The dominant chord introduces instability, which is resolved by returning to the tonic.

Dominant is also a term applied to specific 7th chords, that utilize a minor 7th interval added to a major triad.

What are extended chords?

Chord extensions are triads that include intervals past the 7th. This includes the 9th, 11th, and 13th chords. For example, a 13th chord includes the 9th, 11th, and 13th scale degrees. But on the guitar, this would mean we have the root, 3rd, 5th, 7th, 9th, 11th, and 13th which would equal 7 notes. As we only have 6 strings this would be impossible to play. In this instance, a note is usually omitted, in most cases the 5th, and in many cases the 9th and 11th.

What are chord functions?

e.g. what is an I-IV-V Chord Progression?

Chord function (aka harmonic function) describes the interaction or relationship between chords. It is influenced by genre and context to some extent e.g. the chord preceding and being played after. Chord function is usually broken down into three specific groups: tonic, subdominant, and dominant, and are represented by Roman numerals e.g. I, IV, V means we play the first, fourth, and fifth chords of a key.

Much of this depends on the notes within a given chord and mostly relates to movement within a chord progression e.g. some chords introduce instability that increases the need for the piece to resolve on the tonic e.g. a more stable chord within the context of the chord progression.
I’ve written a much longer piece here that describes chord function and how to know which chords work well together.

What are diatonic chords?

Diatonic means ‘in key’ so diatonic chords are simply chords within a given key.

What is a chord inversion?

The term inversion means to reverse position. In the context of chord theory, an inversion means we change the structure of the chord without changing the chord’s value e.g. the root is the lowest note of a chord usually, but if we voice the chord so that the third interval of the chord is the lowest note it would be known as a first inversion. If the fifth was the lowest note it would be a 2nd inversion chord.

What are slash chords?

If you see a chord written like this G/B The G indicates the chord e.g. G Major. The B indicates we are to add a B in the bass, making it the lowest note. In the case of a G Major chord, the B is the 3rd, however, if written as G/B we are instructed to make the B the lowest note in the chord, so the first inversion of G (as discussed in the answer above).

Not all slash chords are inversions, however, meaning we can also include non-diatonic (not of the same key) notes.

Summary

While there is far more I could write about chord theory, hopefully, this article has helped explain the basics while avoiding getting too technical. I know from experience that once you have a basic understanding of how chords are built and how they relate to scales and the notes of the fretboard it can really help with writing and also learning songs.

If your focus is on becoming a better guitarist or songwriter the basic music theory covered in this series (learning the notes of the fretboard, understanding scales, and the information included in this article) covers the basics and is all you need to know as a guitarist. However, the language of music is incredibly interesting and I’d recommend doing further research if you want to take your understanding of music further.

Guitar Chord Theory [Quick Guide]