Chord theory

Welcome to a short introduction of the theory behind chords. You will learn how a chord is built and what separates different groups of chords. In addition, you will learn the function of chords and how chord progressions can include chords that don't belong to the musical key. See also general music theory.

The reasons behind the chords names

In the cases there we only have a letter, such as C, it's a common major chord. A major chord consists of three notes: the 1st, the 3rd and the 5th notes in the scale. In what scale, you may ask. In the C major scale we have these notes:

C – D – E – F – G – A – B

For a C major chord we can locate the 1st, the 3rd and the 5th as C, E and G. If you're interested to learn guitar scales, see scale diagrams and more information.

Sometimes we find chords with names such as Cm, Dm and Em. The “m” stands for minor and in a minor chord we have three notes: the 1st, the minor 3rd and the 5th. The notes in Cm are C, Eb (E flat) and G, which all are included in the C minor scale: C – D – Eb – F – G – Ab – Bb.

In the majority of chords, the 3rd decides whether a chord is major or minor.

You may ask how it comes that we only have three notes in a C major chord when you have learned to strum five strings playing this chord:

C chord
C major chord

The reason is the instrument. The notes are ordered less symmetrical on the guitar's fretboard opposed to the piano keyboard. Another reason is that the musical context differs between piano and guitar: you cannot play the harmony with your left hand and the melody with your right hand simultaneously on the guitar. Therefore, we don’t need to worry about too many notes being played at the same time.

As you can see in the diagram above, five notes are played together in a C major chord. These are C (5th string) , E (4th string), G (3rd string, played open), C (2nd string) and E (1st string, played open). It's the most practical way to play the open C chord in standard tuning.

In chords, we often find numbers after the letters: C5, C7, and C9 to list a few. In a C5 chord (also called power chord), we only have two notes: the 1st and the 5th. That's pretty unproblematic. Therefore, the C5 consist of C and G.

In the case of the seven, things are little messier. First of all, there are three groups (or families): 7th, m7 and maj7. C7 is called the C dominant 7th. A C7 consists of the C minor chord plus the flat 7th (but it's not a minor or a major). The flat 7th in C7 is a B flat (Bb). In a Cm7 chord we add the flat 7th to a C minor chord. Finally, in a Cmaj7 chord we add the major 7th (B) to a C major chord.

The 7, m7 and maj7 are all four-note chords. More notes could be added, which is true for the extended chords, with names such as C9, Am11, Emaj13.

Different chords names refers sometimes to the same groups of notes, so- called enharmonic chords.

Chord versions and fingerings

There are many versions, or fingerings, of chords. For example, the D chord could also be played as this:

D no 3rd chord diagram
D chord, alternative fingering

This chord fingerings can be described as D with A on the top, meaning a D chord in which A is the highest note.

The next diagram shows an alternative fingering for the A chord:

A chord diagram
A chord, alternative fingering

This chord can be written as AV, meaning a A chord in fifth position. Another version is AIX (X X X 9 10 9), indicating a A chord in ninth position.

Chord comparisons

You may wonder what actually differ between chords such as C9 and Cadd9 or C13 and Cmaj13. Here are the answers from a tone perspective:

The difference between 9th and add9 is the flattened 7th.

C9: C, E, G, Bb, D

Cadd9: C, E, G, D

The 9th chord includes all the tones in a 7th chord and is extended with a ninth.

The difference between 9th and 7(#9) is a raised ninth

C9: C, E, G, Bb, D

C7(#9): C, E, G, Bb, D#

C7(#9) is an altered ninth chord, quite uncommon, but it's not impossible you will encounter it.

The difference between 13th and major 13th is a flattened and a natural 7th.

C13: C, E, G, Bb, D, A

Cmaj13: C, E, G, B, D, A

When memorizing, you are helped by thinking about the 7th versus maj7 and when add two notes to each.

On this site, you find lots of other chords, such as sus chords and slash chords. These chords have special sections and are explained together with its theory. You could get supplementary knowledge by reading What is a guitar chord?.

The connections of chords

It's easy to hear if chords sound pleasant played together.

Diatonic – the consonant relationship

Some chords are connected to each other in the way the notes belong to the same scale. For example:

C - Dm - Em - F- G - Am - Bdim

These seven chords have notes that all belongs to the C major scale, they are therefore diatonic. Try to play some of them in different orders and you can hear that they fit together.

These chords can be divided in principal chords and secondary chords. The principal chords in this case are C, F and G, whereas the secondary chords would be Dm, Em and Am (Bdim is of less significance).

The same thing could be done with four-notes chord types:

Cmaj7 - Dm7 - Em7 - Fmaj7- G7 - Am7 - Bm7b5

Once again, all these chords have notes that belong to the C major key and once again you can play them and hear that they fit well together, their relationship is consonant.

Discord - the atonal relationship

It's also possible to include atonal chords, which is chords that doesn't fully match the notes in the key. One such replacement is VI7 instead of vi. For example, A7 instead of Am in the key of C major; a chord progression could be: C - A7 - Dm - G.

When non-diatonic chords are placed in progressions they are "borrowed" from related keys. For example, the iii chord can be replaced by a III chord. To exemplify this, the progression C - Em - Am - G could be transformed to C - E - Am - G. The latter include some, but not much, dissonance.

See the Chart with chords sorted by key for an overview of the same thing in different keys.

Chords and intervals

The notes in chords are often referred to as intervals, such as a third or a fifth. It's important to understand the concept of intervals. Principally it's quite easy – you need to be able to count to thirteen and what you are counting are scales steps …

Scales steps 1 2 3 4 5 6 7
C scale C D E F G A B
C chord C   E   G    

The relationship between intervals, chords and scales are illustrated by comparing a C major scales and a C major chord from the perspective of scale steps. You can see why the second and third note in a C chords (as well as other major triads) are referred to as third and fifth. The first note is not called the first, which wouldn’t be illogical.

The next table show the relationship between a sixth and a thirteenth chord. Notice that both C6 and Cmaj13 include the sixth interval, but on different octaves (that's the reason it's good to be able to count to thirteen).

Scales steps 1 3 5 6 7 8 9 11 13
C6 C E G A B        
Cmaj13 C E G   B   D F A

The relationship between intervals, chords and scales are illustrated by comparing a C major scales and a C major chords from the perspective of scale steps. You can see why the second and third note in a C chords (as well as other major triads) are referred to as third and fifth.

That is clear and simply, isn’t it? It can, however, be a little more complicated. You may encounter terms as major third and minor third, perfect fifth and major seventh and minor seventh. Let’s take a closer look on by change the C Chord from the previous table with a Caug chord instead:

Scales steps 1 2 3 4 5 6 7
C scale C D E F G A B
Scales steps 1 2 3 4 #5 6 7
Caug chord C   E   G#    

The augmented chord (abbreviated aug) consist by a root, a third and an augmented fifth. The augmented fifth are G# note, a G with a sharp (#) sign, and therefore outside the C scale. The correct scale step for this note is written as #5, indicating that it's a tone one semi-step above G.

Here comes a third example:

Scales steps 1 2 3 4 5 6 7
C scale C D E F G A B
Scales steps 1 2 3 4 5 6 b7
Caug chord C   E   G   Bb

The dominant seventh chord (abbreviated 7 or, less common, dom7) consist by a root, a third, a fifth and a minor seventh and as can be noted from the table doesn’t fully match the C scale. In C7, the minor seventh is Bb, a B with a flat (b) sign. The correct scale steps for this note is written as b7, indicating that it's a tone one semi-step below B.

As you have seen, it's not always enough to describe the intervals in a chord by third, fifth, seventh and so on. Sometimes, there are anomalies and in such cases the intervals are pinpointed by additional information such as “minor” (third), “minor” (seventh) and “perfect” (fifth).

When omitting notes, strange things that can happen

A normal guitar has six strings, but a chord could include more than six tones. This is taking care of by omitting some of the least important notes and is not a big deal in most cases, even a pianist with ten fingers available often omit notes in four-notes chords and above.

But in some cases, odd things can happen. For instance, major 11th and minor 11th chords could be played identical on the guitar.

For example, this chord in short notations: X02030. As the chord is played, it includes the notes A, E, G, D and E. These tones are included in both A11 and Am11:

A11: A - C# - E - G - B - D

Am11: A - C - E - G - B - D

Because of the omitted notes, the "left-over" notes will be the same. Ideally, cases like these are avoided, but if you happened to see major and minor chords that are identical, you know why it could be.

For more in-depth reading, see: The Chord Theory ebook