Chord theory 1 - triads

This is the first of four pages about chords. Each page dives into the details about one particular kind of chord:

1. triads
2. seventh chords
3. added note chords
4. extended chords

Along the way we introduce a lot of ideas, which will help you to understand how chords work.

On this first page, we take a look at:

• what is a chord?
• what is an interval?
• what is an octave?
• how to build triads
• what is the root note?
• what is a chord factor?
• what is an inversion?
• what are voicings?
• different kinds of triad
• suspended 4th chords

What is a chord?

Let's start with the most fundamental definition:

You can play a chord on a single instrument like a guitar, or a piano. You can also play a chord on other stringed instruments like a harp, and on other keyboard instruments like an organ. A accordian even has keys to play chords.

Other instruments may only play a single note, but when played together in a group, they also play chords. This might apply to a string quartet or a horn section.

The same is true of group of singers in vocal harmony. The notes sung by the individual singers also form a chord.

There are very many examples of broken chords in classical and popular music, for example:

• Moonlight Sonata, by Beethoven
• Prelude in C Major, by J.S.Bach
• Someone Like You, by Adele
• Stairway to Heaven, by Led Zeppelin
• House of the Rising Sun, by the Animals
• The introduction to Clocks, by Coldplay
• The introduction to Your Song, by Elton John
• The guitar introduction to L'appuntamento, by Ornella Vanoni
• The "finger picking" guitar style of Doc Watson

In fact, chords are everywhere in western music.

What is an interval?

The smallest interval in western harmony is a called semitone.

That is the interval between two adjacent keys on a piano, or two adjacent frets on a guitar. Other intervals can be measured in the number of semitones that they contain.

We're going to come back to intervals later, when we discuss chord factors. For now, it is enough to introduce the two most important intervals for building chords:

• a minor third, which is 3 semitones
• a major third, which is 4 semitones

What is an octave?

One interval is of such central importance, that we should discuss it separately.

This is not a lesson in physics and I am not going to start explaining sound waves. The important thing is, if one note is an octave higher than another note, then it sounds the same, just higher.

What this means for chords is, that if you swap out one note for another note, which is one octave higher, then the chord will sound more or less the same.

This will be very important when we start discussing inversions.

Octaves on the piano

You have probably noticed that the piano keyboard has a repeating pattern.

This basic pattern is repeated multiple times

In fact it is repeated seven times:

Octaves on the guitar

When you hold a guitar string down at the 12th fret, you shorten it to half of its original length. That doubles the frequency of the sound wave generated by the string.

When you shift any note up by 12 frets, you are shifing it up by exactly one octave.

This diagram shows an E major chord in its base position, and shifted up by one octave.

Of course, there are other ways to play an octave on the guitar, but they are not so easy to visualize.

How to build triads

The simplest way to build a chord is by stacking thirds, to a build a chord which is called a triad.

Using only the major and minor thirds, there are four combinations, which gives us four kinds of triad.

That is already quite absract. Let's look at what that means on a piano or on a guitar.

Triads on the piano

On a piano, taking all the white keys and black keys together, the step from one key to the next is always a semitone.

The block of keys shown below represents one octave on a piano.
Let's say we start at the first note, which is a C.

If we go up by a major third, where do we end up?
A major third is equivalent to 4 semitones, so counting upwards (to the right) we end up at E.

Carrying on from the E, if we go up by a minor third, where do we get to?
A minor third is equivalent to 3 semitones, so counting upwards again, we end up at G.

Together, a major third and a minor third combine to form a major triad.
Since we started on the note C, this chord is called a C major triad.

Triads on the guitar

Now let's look at the same thing on a guitar, and once again, let's start with the note of C. You can play C at different places on a guitar, for example at the third fret on the fifth string.

Each fret on a guitar is equivalent to one semitone. So if you move up one fret, the note goes up one semitone.

A major third is equivalent to 4 semitones, so to go up a major third, we have to go up 4 frets. This brings us to the note E.

Let's keep it easy and only use one string.

Carrying on, a minor third is equivalent to 3 semitones, so to go up a minor third, we have to go up another 3 frets. This brings us to the note G.

Still staying on one string, this gives us the intervals of a major triad (4 frets) and a minor triad (3 frets).

Since we started on the note C, this chord is called a C major triad.

On a guitar, it makes sense to move the notes onto different strings, which gives us.

What is the root note?

You may recall from above, that we said:

The simplest way to build a chord is by stacking thirds.

If we stick with that idea, then the root note is the note at the bottom of the stack.

This gives us a basic organizing principle for chords. Each chord has:

• a set of intervals used to build the chord
• a root note as the base of the chord

Things will get a bit more complicted when we look at inversions, but for now we can assume that the root note is always the lowest note in a chord.

Building triads on different roots

So how does it work, when you use a different root note?

D major triad

Above, we showed a C major triad on a piano and on a guitar. What if we started with D instead of C.

Well that's easy. We just start at D and go up 4 semitones to F♯ and then 3 semitones to A.
Here it is on the piano keyboard.

and on a guitar.

On a guitar, you could play the notes on different strings, like this.

G major triad

Let's look at another example, say a G major triad.

On the piano keyboard, it looks like this

and on a guitar it looks like this

On a guitar, you could play the notes on different strings, like this.

C♯ major triad

So far, the chords have all started on white notes on the piano keyboard.

It makes absolutely no difference if we start on a black note, for example a C♯ major triad.

Of course, on a guitar, there are no black notes.
The C♯ major triad just looks like the C major triad shifted up one fret.

Or

Aside:
Specialists might prefer to describe the second note as E♯, rather than F.

Barre Chords

As we already said, the organizing principle for Chords is:

• a set of intervals (or the shape of the chord)
• a root note

For guitar players, this is easily illustrated with barre chords.

The simplest barre chord is based on the shape of an E major chord.

To play a barre chord, you place your index finger across all six strings of the fretboard, and use exactly the same fingering relative to the position of your index finger.

Let's look at some examples. Here is a G major barre chord

an A major barre chord

and a B major barre chord

The root note is the position of the barre on the lowest (or the highest) string.

The shape of the chord (or its fingering) makes it a major chord.

What is a chord factor?

So far, we have described a major triad as a major 3rd followed by a minor 3rd. That's a good way to describe how the chord can be built, using the technique of stacking thirds.

Another way to describe a chord, is by describing each note by its relationship to the root note.

There are two ways to do this

• using the interval above the root
• using the chord factor

We have already met the intervals of minor third and major third, and we know that the interval between the C and the E in a C major triad is a major third.

If we want to describe the interval between the C and the G, then we need to learn a new interval which is the 5th, sometimes called a perfect 5th.

The interval above the root defines the exact number of semitones above the root note. A major third is exactly 4 semitones above the root. A 5th is exactly 7 semitones above the root.

If you are interested, you can find a complete list of intervals on a separate page about intervals.

The chord factor tells you the role that a note plays in a chord, but it doesn't tell you the exact position of the note.

All triads have the chord factors 1, 3 and 5, which means they all contain a root, a 3rd and a 5th,

Here are the intervals we are going to meet when we discuss the other triads:

As you can see, the name of the interval always reflects the chord factor. If the chord factor is 3, then the interval is some kind of 3rd. If the chord factor is 5, then the interval is some kind of 5th.

Note:
If you learn more about music theory, you will meet the term scale degree.
This is almost the same as the chord factor, with this difference:

• the chord factor describes the position of a note within a chord, relative to the root of the chord
• the scale degree describes the position of a note within a scale, relative to the tonic of the scale

Later we are going meet other chord factors. In the first octave, we can use the chord factors 1-7. For extended chords we can also use the chord factors 9, 11 and 13.

It can be useful to describe the chord factors in a chord as a list, for example 1-3-5, or 1-3-5-7.

Note:
Some authors apply acccidentals to chord factors, for example ♭3 or ♭7, to specify the exact interval from the root.

I am not going to follow that usage. In these articles, I will use the chord factor to indicate the role of a note in a chord, but not the precise interval from the root.

Chord factors in the diagrams

You will have noticed, that the diagrams of the piano keyboard and the guitar fretboard use different colours for the notes. These colours correspond to the chord factor.

(The specific colours are quite random and have no meaning outside these pages.)

From now on, we will show the chord factor as a number in most of the diagrams, for example:

What is an inversion?

Remember what we said about octaves?
If one note is an octave higher than another note, then it sounds the same, just higher.

We are now going to use that to build inversions.

Inversions of the C major triad

Let's look at what happens if we do this repeatedly, based on the C major triad.

And here's the thing. They all sound the same!

Of course, they don't sound exactly the same, because the lower ones sound lower and the higher ones sound higher, but when you hear these inversions, you seem to hear the same chord.

Let's take a look at it on the guitar:

Inversions look like different chords, but they aren't

This is the important thing about inversions.
They look different, but we consider them all to be the same chord.

The three inversions all contains the same chord factors, root, third and fifth.

Remember when we said the root note was at the base of the chord? Now you can see, that that isn't always true.

Reordering the notes

We have seen above that there are three inversions of the C major triad:

• C-E-G (root position)
• E-G-C (1st inversion)
• G-C-E (2nd inversion)

We can generate three more versions of the same chord, by keeping the lowest note the same, but swapping the other two notes around. This gives us the chords:

• C-G-E
• E-C-G
• G-E-C

Let's look at these on the piano keyboard.

and on the guitar

Voicings

We have seen that a major triad contains the chord factors root, major 3rd and 5th.

We have now made 6 different voicings of the chord by placing the notes different orders:

• root, 3rd, 5th
• root, 5th, 3rd
• 3rd, 5th, root
• 3rd, root, 5th
• 5th, root, 3rd
• 5th, 3rd, root

All of these are different versions of the same chord.

What we learn from that, is that the order of notes in a chord doesn't really matter.

What are the four types of triad?

You may remember this table from earlier on this page.

By stacking thirds you can create four different triads, but so far we have concentrated on the major triad.

One way to get a feel for these triads it to look at what chords we can play by using only the white notes on the piano.

Major triad

If we play a triad on the white notes starting on C, F or G, then it will be a major triad.

These three chords, which are called the tonic, subdominant and dominant in the key of C, are extremely common in pop and rock and blues.

Minor triad

If we play a triad on the white notes starting on D, E or A, then it will be a minor triad.

Wheras major triads have a triumphant, happy feeling, minor triads feel a bit more subdued or thoughtful.

Major and minor triads are form the harmonic basis of all kinds of western music and they are both very common.

Diminished triad

If we play a triad on the white notes starting on B, then it will be a diminished triad.

Using only the white notes on a piano, we can build 3 major triads, 3 minor triads, but only one diminished triad.

Based on that alone, you might guess that diminished triads would be used less than major and minor triads, and that would be correct.

Diminished triads are typically used as passing chords in a chord sequence.

Later, we will discuss the diminished 7th chord, which has some very interesting characteristics. The diminished 7th chord is formed by stacking 3 minor third intervals. The diminished triad behaves something like a diminished 7th chord, but with one note missing.

Augmented triad

As already noted, using only the white notes on a piano, we can build 3 major triads, 3 minor triads and 1 diminished triad.

Using only the white notes, you cannot build any augmented triads.

This is what the augmented triad with the root C looks like on the piano keyboard.

Augmented triads are used even less than diminished triads, and typically as a passing chord in a chord sequence.

Suspended 4th chords

There is one more important 3-note chord, which technically is not a triad.

The suspended 4th chord is formed using the chord factors root, 4th and 5th.

On the piano, this is what a C Suspended 4th chord looks like:

Very often, a suspended 4th (or sus4) is followed by a major triad, simply by moving the 4th down one semitone.

It is called a suspended 4th, because of the feeling that the fourth is suspended above the third, and is about to fall.

A characteristic example is the acoustic guitar intro to Pinball Wizard by The Who, which repeatedly switches from a Sus4 to a major chord.

The importance of thirds in the chordle game

In the suspended 4th chord, we can consider the 4th as a substitute for the 3rd in the chord.

From that point of view, there are three possible kinds of third:

• minor 3rd
• major 3rd
• suspended 4th

All chords in the chordle game contain one of those three notes.

That is to say, all chords in the chordle game contain a 3rd note, or a suspended 4th as a substitute for the 3rd note.

Note:
Technically, there are some possible chords (like a sus2 chord) which do not obey this rule, but these notes are not included in the chordle game.