Guitar Music Theory

by John Lyons

Guitar Theory

There are 4 things you need to know about guitar theory, these are:

  • Guitar scales and intervals
  • Chord construction
  • Understanding musical keys
  • How to use all of these elements in your playing!

Guitar theory can be a daunting prospect for many guitarists. However, it’s vital to know if you want to take your playing to the next level.

Guitar theory is a HUGE subject, so don’t expect to learn it all in one go. Take it one step at a time.

String Names

There are 6 strings on the guitar.

The strings are named from low to high: E-A-D-G-B-e

  • The 1st guitar string produces an e note. This is also the thinnest string on the guitar. Sometimes this string is referred to as the high-e. The name of the string is often shown in lowercase to distinguish it from the low-E.
  • The 2nd guitar string produces a B note.
  • The 3rd guitar string produces a G note.
  • The 4th guitar string produces a D note.
  • The 5th guitar string produces an A note.
  • The 6th guitar string produces an E note. This is also the thickest string on the guitar. Sometimes this string is referred to as the low-E since it produces the lowest note.

Note names and scale degrees

Music is a language of it's own. Names of notes are named like in the Alphabet. In music , only the first 7 letter of the alphabet are used.

You may well already know that pitch is communicated by a series of letters (A, B, C, D, E, F, G). Instead of going onto H-I, etc.. it starts again at A. This run of 8 notes from A-A or B-B, C-C, etc.. is called an octave. These notes can be played on any tuned instrument. So, on a piano, the notes correspond to the following keys….

C major scale on fretboard diagram

C major scale guitar TAB


An interval is the distance between any two notes.

When we talk about intervals, we tend to talk about their relation to the root note. Root note is simply the first note in a scale.

Intervals have scale degrees as well as qualities.

Scale degrees are expressed in numbers ex. 1st, 2nd, 3rd etc.

Qualities are expressed as Major, Minor or Perfect.

This means, that if our root note is ‘C’, the rest of the notes in the scale have an individual relationship with the note C.

We can apply a similar concept to the minor scale, however this time the minor scale has a different root note, (in this example the root note is A), so this means that the perspective of the intervals change.

Try and use your instrument to understand guitar theory.

For example when you play your major or minor scale, you should:

  • Visualise what each interval looks like compared to the root note.
  • Listen to what each each interval sounds like compared to the root note.

When we learn a scale, it’s easy to find the root note and blast through the pattern without even thinking about what any of the notes are called.

Try this as a challenge:

  • Play the C major and A minor scales and name the notes as you play the scale.
  • Play the C major and A minor scales and name the intervals as you play the scale.

It’s important to understand this, as intervals and scales help us to construct chords.

Why should I learn intervals?

In music, there are two ways to label pitches - alphabetical notes (A - G) and numerical intervals (1 - 7). Most guitarists take some time to learn the notes of the musical alphabet and where each note lies on each string/fret. But while this is valuable, the benefits of knowing intervals is often overlooked.

People often ask me about the numbers I use in many of my diagrams. If you're not familiar with intervals, they can look a bit strange - e.g. ♭7, ♯4, ♭5 etc.

Before we learn more about what these labels mean, we first need to understand why it's worth just as much, if not more of our time to learn intervals as it is notes.

In short, both labels serve different functions in terms of how they "measure" pitch.

Notes = Absolute Pitch

Each pitch we can create on guitar can be given an alphabetical label, A through G. This is primarily useful for finding a chord or scale root.

For example, if you see C major (or Cmaj) written down, you'd typically find C on the neck first and build a major fingering shape around that root.

Similarly, if you wanted to play A minor pentatonic, you would most likely find A on the neck first and build the minor pentatonic scale pattern from there.

We could also work out the individual notes that make up a chord or scale, above the root. For example, Cmaj contains the notes C, E and G.

The A minor pentatonic scale contains the notes A, C, D, E and G.

But as I'll get to in a moment, this isn't really necessary (and it's very time consuming).

So these alphabetical note labels are best used to locate single, specific pitches, known as absolute pitch.

Intervals = Relative Pitch

Intervals are a slightly different way of finding pitches on the neck and have more to do with musical relationships.

Intervals occur between two pitches. They are a way of measuring the distance between notes. Therefore intervals are about relative pitch - the relationship between notes.

Intervals are, therefore, the true building blocks of music, since music is made when two or more pitches either harmonise (play together) or form a melody (move from one pitch to another).

For example, going back to our C major chord, its interval formula would be 1, 3, 5 (don't worry if you don't know why we use 3 and 5, that'll come later).

However, the 3 and 5 are relative to the root, so whichever root we use - C, D, E, F etc., the formula of the major chord will always be 1, 3, 5, regardless of how the note labels change.

"So How Is This Useful?"

Instead of having to learn the notes that make up every single chord and scale, across all 12 roots, intervals allow you to learn in movable patterns and shapes.

And I'm not just talking about memorising a fingering. It's about being able to identify each pitch within a chord or scale so you can confidently target specific pitches on any root or in any key, without having to know its note labels.

If you're scratching your head (I don't blame you! Bear with me!), this table may help to clarify why knowing intervals is like a "short cut" to knowing chords and scales in every key...


So as you can see, every single major chord, no matter what its notes, can be referenced using the interval formula 1 3 5. Even though they all contain different notes, they can all be seen as part of the same interval family.

The only thing that changes is the root, and therefore the overall pitch (higher/lower) of the chord. But the chord itself looks and even sounds the same, once you learn to see and hear music in intervallic terms.

In purely intervallic terms, C major is the same as E major, F major, G major etc.

In purely intervallic terms, A minor pentatonic is the same as B minor pentatonic, E minor pentatonic, G minor pentatonic etc.

Once you learn how an interval formula appears as a uniform, repeating pattern on the guitar neck, all you need to do is move it to the appropriate root or "starting position". The pattern never changes its structure, its notes never change their relative position.

In fact, that's why we have movable scale patterns and chord shapes - it's really just a bunch of related intervals that make the same sound (hence why we use the same numbers), just higher or lower in pitch, depending on the root we're using.

The movement/distance between 1 and 3 in interval terms is the same whether we're playing C and E, D and F♯ or G and B.

All you really need to know in terms of notes is the root of the chord or scale you're playing, a reference point for starting your pattern or shape, and you'll already know this root because it's right there in the chord name (Cmaj, A minor pentatonic). The rest is all relative interval patterns that you only need to learn once for each chord or scale "family".

But It's Not Just About Saving Time

Learn to see the fretboard like this and something quite amazing will happen...

You'll start to see the entire neck as one big connected roadmap. Chords, arpeggios and scales will merge into the same musical expression. You'll see a connection between chords and their related scales, and vice versa.

This connection will reveal itself in many ways as you progress in your learning.

For example, knowing intervals allows you to see that 1, 3 and 5 of the major chord exist in the following scales...

  • Major pentatonic - 1 2 3 5 6
  • Major scale - 1 2 3 4 5 6 7
  • Mixolydian - 1 2 3 4 5 6 b7
  • Lydian - 1 2 3 #4 5 6 7
  • Phrygian Dominant - 1 b2 3 4 5 b6 b7

That's what makes these scales compatible with major chords.

It would be far more difficult to see this relationship if you learned each scale purely by its notes, because the notes would be different depending on the root you were playing the scale on. The pattern would be hidden in the alphabet soup!

In short, intervals show you how different musical elements - melody and harmony - are intrinsically related, no matter where you play them.

Intervals Are the Key To Unlocking Amazing Ear Skills

Intervals form on the guitar neck as movable patterns. But we can also use intervals to help us with ear training.

Most musicians will never have the ability to name a pitch or group of pitches they hear, without any other reference, purely by note, known as absolute pitch recognition. It's a very rare skill and not necessary to have.

But being able to identify intervals by ear, known as relative pitch recognition, is something anyone can learn given a little practice. The value of having this skill is that you'll be able to pick up music purely by ear.

Even if you can't find the exact key it's played in, you'll be able to hear and replicate the movement, the relationship between notes - that's what makes the music happen.

"So Will I Ever Need to Know The Notes of a Chord or Scale?"

It really isn't necessary. As I mentioned, the value in knowing the notes on the neck is to be able to find a root, a single reference point for a pattern or shape. The rest is all about interval formulas.

Relative pitch is far more valuable to master than absolute pitch, both visually and auditorily. Intervals are what we use to turn notes into music.

Basic Guitar Fret Intervals - Half & Whole Steps

This lesson on guitar fret intervals follows on nicely from learning the notes on the fretboard and note relationships.

Now we're going to look at how intervals work on your guitar's fretboard.

Intervals can be seen as the space or distance between two pitches/notes. The larger the distance between the pitches, the larger the interval.

So, for example, the interval between the notes A and C is larger than the interval between A and B.

A bunch of intervals from the same starting note creates a chord (when they're played together) or scale (when played one after the other). So intervals can be seen as the building blocks of music. We'll look more at this in a coming part. But first...

Half Steps & Whole Steps

As you delve into guitar theory, you'll hear people talk about whole steps (also called whole tones, abbreviated as W or T) and half steps (also called semitones, abbreviated as H or S).

Well, what they're referring to are intervals - the distance between two notes.

Half and whole steps are the smallest intervals/movements on the fretboard.

See the diagrams below for how these interval "steps" would appear on the neck...

That's how half step and whole step intervals would appear on one string. It's the same spacing whichever string you're on:

  • Half steps are the equivalent of one fret between the starting note and destination note.
  • Whole steps are the equivalent of two frets between the starting note and destination note.

So if we were to move from the 3rd fret up a whole step we would end up at the 5th fret.

If we were to move from the 5th fret down a half step we would end up on the 4th fret.

If you see a scale written like this...'ll know what the W's and H's (Whole steps and Half steps) mean and you should at least be able to visualize the scale across one string, using the whole and half step fret intervals.

You may also see scales written using a series of 1's and 2's. That's 1 for a half step and 2 for a whole step (as 2 half steps make a whole!).

For example, the above sequence might be written as: 2 2 1 2 2 2 1

Or as: W W H W W W H

Or as: T T S T T T S (T = whole tone, S = semitone)

Now, we'll want to use these intervals across more than one string, so we need to know how these intervals appear vertically, from string to string, as well as horizontally.

Half/Whole Steps Across More Than One String

Let's look at a few diagrams to see how these same whole and half step intervals appear between two adjacent strings.

Grab your guitar and play these positions so you can hear the sound of the interval, moving both up and down.

Count how many frets wide the interval appears. Why is this necessary? Because knowing where intervals appear in several places on the fretboard will make scale and chord improvisation easier.

Half Step Between 6th and 5th String

Whole Step Between 6th and 5th String

Both these relationships are the same for the bottom four strings: E-A, A-D and D-G.

However, because the B string is tuned differently in relation to the G string, we have to compensate by adjusting the relationship on the fretboard:

Half Step Between 3rd and 2nd String

Then it's back to the same fret spacing as before between the B and high E string...

Whole Step Between 3rd and 2nd String

Half Step Between 2nd and 1st String

Whole Step Between 2nd and 1st String

Whole and half step intervals are the building blocks of scales and movements between chords, so being able to see these relationships across all six strings is hugely beneficial, even if it doesn't seem that big a deal right now. These are the kind of visual references that will help you navigate the fretboard musically and without hesitation.

Along with the note patterns you learned in the previous lesson, you'll be able to jump between note positions based on the interval relationships you map out on the fretboard. This in turn means there'll be less time spent on trial and error and more interconnectivity between the different concepts we'll explore in future lessons


Major Scale

The first step in understanding guitar theory is learning guitar scales. A scale is a group of musical notes.

In music we have two basic types of scales, those are:

  • Major scales.
  • Minor scales.

Both scales are used to create different types of sounds, major scales have a ‘happy’ sound and minor scales have a ‘sad’ sound.

They both have their uses in all kinds of music.

In today’s lesson we’re going to talk about our scales in the key of ‘C’.

The major scale is used extensively in western music, regardless if pop, country, rock, etc.

C major scale example:


The major scale formula is

whole step - whole step - half step - whole step - whole step - whole step - half step

TIP: half steps always between B & C, E & F

Below is the C major scale on the guitar starting on the 8th fret of the low E string:

Understanding chord construction is really useful when understanding guitar theory.

This helps us to understand:

  • How chords are built harmonically.
  • Why certain notes of a chord work better with certain notes in a scale.

Guitar chords are built from each note in the scale. Here’s a really simple way to build chords off of scale. In today’s lesson, we’re going to apply this to the C major scale.


Pick your root note, this can be ANY note in the scale. However, for today’s lesson we’re going to use the note ‘C’.

After we’ve picked our root note, we skip across two notes to the 3rd note.

This means we now have the note ‘E’.

After this, we move across two notes again to the note ‘G’.

Therefore the notes in a C chord, are the notes C, E and G.

The notes we have chosen are the 1st, 3rd and 5th note in chord. This is what’s known as a triad.

All major and minor chords, are created by using the 1st, 3rd and 5th notes. To change the chord, we just change the root note.

Like this:

You can build a chord off of each note in the scale. However, for each note in the scale, we get a different chord type.

So for notes:

  • 1, 4 and 5 we have major chords.
  • 2, 3 and 6 we have minor chords.
  • 7 we have a diminished chord.

This means in the key of C, notes 1, 4 and 5 are C, F and G. Therefore the chords are C major, F major and G major.

The 2nd, 3rd and 6th notes are D, E and A. Therefore the chords are D minor, E minor and A minor.

The seventh note in a C major scale is B, so we have B diminished.

Now we understand how chords are built, lets take a look at how this works in a key.

Musical Keys

The definition of a musical key is often thrown around, this often means it can be difficult for guitarists to understand what they are.

Musical keys are a collection of notes that work well together. However, a musical key also contains chords that work well together.

We’ve already established that a C major scale has the following notes:


And that we can build chords off of those notes:

  1. C major.
  2. D minor.
  3. E minor.
  4. F major.
  5. G major.
  6. A minor.
  7. B diminished.

These notes and chords are what make up the key of ‘C’.

Guitar chords in the Key of C major

Guitar chords in the Key of D major

more to come...