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Guitar Theory [Where To Get Started]

While many people avoid it, learning guitar theory (music theory for guitar) can be incredibly useful. But, where do you start? Do you begin by learning how chords are constructed? or should you start by learning scales and how they relate to chords? Alternatively, wouldn’t it also make sense to memorize the notes of the fretboard?

While they are all equally important if learning guitar theory, first learn what an octave is and how it’s divided equally into 12 notes. Next, learn the order of those notes (chromatic scale), what enharmonic notes are (sharps and flats) and what half and whole steps are. Next, learn the major scale, and how it’s built in relation to other scales, along with key signatures, before learning how chords are built from the major scale.


All sound is vibration

One of the most useful things to understand when it comes to guitar theory is how sound is created.

Put simply, all sound is vibration.

When something vibrates (e.g. guitar strings, vocal cords) pressure waves are created known as sound waves. Soundwaves displace surrounding air particles, setting off a wave-like series of vibrations that are detected and amplified by the inner workings of the ear before being perceived by the brain as sound. 

Pressure waves, known as sound waves
Soundwaves demonstrating high and low-pressure areas.

The diagram above shows areas of high and low pressure.  When the tuning fork is struck, it vibrates backward and forward. As it moves forward the air in front is compressed. As it moves backward the pressure drops (rarefaction) and the air is drawn toward the area of rarefaction which builds up in pressure and is projected forward again as the fork vibrates forward. This pattern then repeats.  


Understanding Pitch

Take that same low E string and place a finger on the fifth fret and pluck the note again. The pitch of the note is raised from E to A. This happens because the length of the string able to vibrate has now been shortened, causing the string to vibrate faster. The faster something vibrates, the higher its pitch

Frequency and pitch

We measure vibrations per second as Hertz (Hz). A low E string has a frequency of 82Hz (82.4 to be exact). When fretting the fifth fret of the low E string (the note A), the frequency increases to 110Hz. 

Soundwaves increase in frequency as the pitch of the note is raised
The wavelength increases frequency as the pitch of the note is raised.

The red lines above represent the section of guitar string able to vibrate. The soundwaves increase in frequency as the pitch of the note is raised.

That’s essentially how the guitar makes sound and how we can control the pitch of notes we play. Everything we do on the guitar is based upon those simple principles.


Octaves

Octave between open string and 12th fret
One octave on the guitar fretboard

Once you understand how sound is created we can move on to octaves. An octave is an interval e.g. the distance between a note and another note that is double the first note’s frequency.

This means, when you play an open string on your guitar and then play the same string at the 12th fret, our brain recognizes it as the same note, just an octave higher. Most guitars have two fret markers at the 12th fret to indicate this. 

The table below shows the frequency of each open guitar string.

Open StringFrequency (Hz)Pitch Notation
1 (high E)329.6E4
2 (B)246.9HzB3
3 (G)196 HzG3
4 (D)146.8HzD3
5 (A)110HzA2
6 (low E)82.4HzE2

As you can see the frequency of the high E string is 329.6Hz (approx.), which is four times the frequency of the low E string, meaning it is two octaves higher which is indicated in the pitch notation column, which is a way to specify musical pitch by octave.

12 tone equal temperament

With all of this in mind, we can now see that all of the notes available in western music are divided within octaves.

Looking back at your guitar fretboard again, we can see we have 12 frets before the notes begin to repeat an octave higher. This means the octave is divided into 12 pitches.

12 tone equal temperament
Open string notes repeat at the 12th fret an octave higher

This is essentially 12 tone equal temperament (12 TET for short), and this really is how western music works. Alternative musical systems around the world have simply broken down the octave into a different number e.g. some middle eastern cultures utilize a 24 TET system.

Why do guitar frets get narrower further up the neck?
Because the length we shorten the string to increase the pitch gets narrower the higher the note we play. Fret spacings get narrower (logarithmically spaced) the higher up the neck we go.

12 tone equal temperament on the guitar

In simple terms all of this means, despite most guitars having at least 120 frets, there are only 12 individual notes, the remaining frets are the same notes, with some in different octaves, as shown in the diagram below.

How to learn all notes on guitar

Everything up to this point may feel unrelated to guitar theory, but understanding how sound is created and then divided into the 12 notes we can play on the guitar helps simplify theory and is the best place to start. 

Everything we are about to discuss from here with regard to the fretboard, scales, and chords are derived from just these 12 notes. 


The Chromatic Scale

When we assemble all of the notes we have available in order we have the chromatic scale, also referred to as the 12 tone scale

The order of the notes themselves simply follows the alphabet (A through to G).

But, didn’t we just mention 12 notes? There are only 7 notes between A and G. 

This is where enharmonic notes, aka sharps and flats, come into play.

Natural and Enharmonic Notes

AA♯BCC♯DD♯EFF♯GG♯
The chromatic scale

The table above shows all of the notes of the chromatic scale (12 tone scale). There are enharmonic notes (sharps) between every note letter except B and C, and E and F. 

We could also write this out as per the example below, substituting flats for sharps as they are the same (enharmonic equivalents). 

AB♭BCD♭DE♭EFG♭GA♭

We mostly use sharps if ascending e.g. going up in pitch and flats when descending, or a mixture of both when writing out scales to prevent showing the same letter name twice.


Half and Whole Steps

An interval is a term used to describe the distance between two notes. 

We’ve already discussed the largest interval, an octave. At the other end of the scale (haha) we have half steps and whole steps (you may know these as tones and semitones in British English).

A half step is an interval between two adjacent notes, which is the same as adjacent frets on your guitar. So, the interval between A and A♯ for example is a half step (or semitone). 

Half Step (aka semitone)
half step (aka semitone)

If we skip a note, the interval is a whole step or tone. So, the interval between C and D for example is a whole step.

Whole step
whole step (aka tone)

Why do we have enharmonic notes? Wouldn’t it be easier to just use the first 12 letters of the alphabet?
Western music has evolved slowly over time based on 7 note diatonic scales. A diatonic scale is any heptatonic scale (a scale consisting of 7 pitches within an octave) that is made up of 5 whole steps and 2 half steps. As a result, diatonic scales utilize all 7 letter names of our musical system. If we had a 12 letter system suddenly diatonic scales become far more difficult to memorize.


Learning the Fretboard

While not strictly guitar theory, the fretboard is the interface of the guitar so having a good understanding of it and where the different notes are found is important.

Thanks to our new understanding of the chromatic scale, we can now familiarize ourselves with the fretboard by learning a few reference notes and then using the chromatic scale to work out the position of other notes on the fretboard.

For example, the 5th string on the guitar is an A. So we also know there is an A on the same string at the 12th fret. 

If you know how to tune your guitar then you will also be able to work out there is another A on the 4th strings 5th fret.

There are a lot of techniques you can use to memorize the fretboard. I have a full article on learning the fretboard here, including some useful hacks.


Learning Scales

Scale Theory

Once you are familiar with the chromatic scale and understand 12 tone equal temperament we can move on to learning about scales.

In simple terms, a scale is any set of ascending or descending notes separated by intervals. 

Scales are important, for both developing your ear and developing your dexterity (skill) and coordination (getting the fretting and picking hand working well together).

Scale Step Patterns

The first and most important scale to learn is the major scale, as it is the ‘master scale’ that other scales including minor scales (harmonic minor and natural minor) reference with regard to how they are put together.  In the diagram below, you can see the major scale pattern e.g. how the major scale is extracted from the chromatic scale.

Extracting the major scale from the chromatic scale

Thinking back to whole and half steps (tones and semitones in British English) the step pattern for building the major scale from the chromatic scale is as follows:

whole – whole – half – whole – whole – whole – half

If that’s not making sense, don’t worry, here’s another example (this time we’re using the C major scale to make things easy as it contains no enharmonic notes). 

C Major Scale

TonicWhole StepWhole StepHalf StepWhole StepWhole StepWhole StepHalf Step
CDEFGABC
8 notes are included to show the half step from the last note of the scale back to the tonic.

All major scales are built using the same step pattern  (whole – whole – half – whole – whole – whole – half) the only difference is the note the scale begins on, the tonic


Tonic and Root Notes

The note you start a scale on defines the key of the scale and is known as the tonic. Tonic and root note are often used interchangeably although this isn’t strictly correct.

Tonic refers to the starting note of scales; a root note is the first note in a chord and defines the letter name of the chord. 


Scale Degrees

Each of the notes included in a scale can be referenced as an individual note, relative to the tonic note by numbers, known as scale degrees. For example, the third note of a scale is the third scale degree, the 5th note is the fifth scale degree (you get the idea).

All of the scales we are about to discuss are referenced against the major scale, so knowing the scale degrees can be useful for building other scales from the major scale.

For example, to construct a minor scale we take a major scale and simply flatten the third scale degree. This means we flatten by a half step the 3rd note in the scale, the scale in then a minor scale.

Each of the scale degrees also has names that describe how they are expressed relative to the tonic note. For example, the 7th scale degree is known as the ‘leading note’ and it is called this because it typically wants to resolve on the tonic e.g. we anticipate the tonic as the next note in sequence for a melody to resolve.

If you are just getting started on guitar I wouldn’t be too concerned with learning these for now, but a good understanding of each can be useful for writing music and working out chords as you progress. 


Guitar Scales

If we consider that a scale is any series of notes (including enharmonic and natural notes) in ascending or descending order we could potentially have thousands of scales (over 20,000 to be exact). But, thankfully when first starting out guitar players should focus on just 5, which are often referred to as guitar scales. 

The major scale, natural minor scale, harmonic minor scale, pentatonic minor scale, and blues scales.

The major scale is the most important in terms of music theory but the Pentatonic minor scale, in particular, is a staple and once you know it will more than likely recognize it in top-line vocals and guitar solos.

You can read my full guide to understanding scales which includes scale charts and tab for each of the scales mentioned above.


Understanding Chords

A chord is any combination of three (or more) different notes played at the same time. Two notes chords, or power chords, therefore, are not technically chords.

There are three categories of chords:

  • Triads
    Made up of
    three notes (the notes are often repeated e.g. E Major consists of 3 separate E notes)
  • 7th chords
    Made up of three notes + a major or minor 7th interval above the root
  • Extended Chords
    Made up of three notes + a major or minor 7th above the root + additional note/s beyond the 7th

We’ll be focusing on triads (the most basic chords), to explain how chords are built but as you can see 7th and extended chords are just extensions of triads.


The Relationship between Chords and Scales

Thirds

Chords are built on stacked thirds. This means the second note of a chord (a triad in this example) is a third above the root note and the third note of a chord is a third above the second note of the chord (a fifth above the root note).

Remember when we discussed intervals earlier? 

A third is an interval that can be either major (spanning 4 semitones), minor (spanning 3 semitones), augmented (spanning 5 semitones), or diminished (spanning 2 semitones).

The quality of a chord (e.g. major, minor) is established based on the type of third the second note of the chord is. So, as you may have guessed, a major chord contains a major third, a minor chord contains a minor third interval.

We’ll just focus on major and minor for now, but keep in mind augmented means to add a semitone to the fifth interval of a major chord and diminished means to reduce the fifth interval by one in a minor chord. 

Using Scale Degrees to Build Chords

Chords can be built using intervals but when first learning guitar theory the simplest way to build chords is using scale degree formulas based on the major scale. This is why I recommend learning guitar theory in the order outlined above.

Below is an A major scale:

ABC♯DEF♯G♯

The scale degree formula for building major triads is 1, 3, 5

This means an A major chord consists of the first, third and fifth scale degree of the major scale:

A, C♯, and E

If we were building an A minor chord instead, our scale degree pattern would be 1, ♭3, 5 

The flat symbol before the second scale degree indicates the note is to be flattened by a semitone making the interval a minor third rather than a major third. With this in mind the notes of an A minor chord are simply:

A, C, and E

All chord qualities have a formula that can be used to build chords from scales. 

For example, an augmented triad uses the following formula:

1 – 3 – ♯5

This means the third scale degree is raised by a semitone. 

If you are interested in learning more about guitar chord theory, intervals and scale degrees click here for a detailed article on guitar chord theory. If you would like to learn more about the relationship between chords and how to know which chords work well together, click here.

Chord Voicings

As we previously mentioned, there are over 120 individual notes on your fretboard meaning the 12 notes used in western music appear across the fretboard in different places. This allows for different chord voicings e.g. changing the structure of the notes within the chord to allow for different expressions of the chord.

For example, most people know how to play an open A major chord on the second fret. But, another way to play A Maj is to use an F Maj open chord shape at the fifth fret and play only the top 4 strings. That’s just one simple example, there are many different ways to play all chords, however the more common chord charts you see online demonstrate the most efficient way to play the chord for beginners. cases.


Summary

If you are anything like me, you may have resisted the temptation to learn guitar theory. My real passion is writing music so I always had a nagging concern that learning music theory would come at a cost e.g. it might take away some of the mystique that came with developing an idea into a song. But, in reality, this is the complete opposite of my experience. Guitar theory has helped me write better music and come up with ideas much faster because I now have at least some familiarity with how music works and how this relates back to the guitar. So, if you are in a similar position, give guitar theory a shot, you really have nothing to lose.

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About Marty

My name's Marty, I've been into guitars for over 30 years. Theacousticguitarist.com is my blog where I write about acoustic guitars, music, and home recording.