2026-10-28
I'm currently attempting to teach myself how to play the guitar. As part of that process I've been trying to learn about music theory. In this article I will walk through the basics of music theory as it relates to guitar. I will be using my own words as I understand things. As a result, I'm not promising that this article covers everything. There are likely some gaps and assumptions. I'll try to link out to additional resources when I know I'm not covering something specific. My goals are threefold:
Each string on the guitar corresponds to a specific note. For this post we're going to assume standard tuning which means that the strings are tuned in this order:
E(thickest string)
A
D
G
B
E(thinest string)
There is a good mnemonic device to help remember this order:
Eddie Ate Dynamite Good Bye Eddie.
Playing any string open plays that string's note. In order to play different notes you can press down the string in the gaps on the guitar neck. These are called frets. Each fret corresponds to a semitone also known as a half step. So, moving up one fret is a half-step and 2 frets is a full-step. As you move up the neck of the guitar, holding down each fret, the notes you play when strumming the string follow a specific pattern:
A -> A# -> B -> C -> C# -> D -> D# -> E -> F -> F# -> G -> G# -> A
It doesn't matter what note you start on, you just follow the pattern from that point. The pattern is circular, when you reach the starting point, you just keep going around. This is illustrated in the animation below.
Note: all animations in this article can be paused and restarted by simply clicking on them
Here's how that looks on the "A" string of the guitar:
There are many different types of scales but for the purposes of this article, we'll be discussing the minor and major scales which are both diatonic scales.
Scales are made up of whole and half steps. As discussed above, on a guitar, each fret is a half step. So, 2 frets for a whole step. If we use the letter "W" to represent a whole step and "H" to represent a half step, we can describe the major and minor diatonic scales as:
Major: W-W-H-W-W-W-H
Minor: W-H-W-W-H-W-W
A scale is named by its root note. So, a G Major scale starts on G and follows the major scale pattern from there. A G Minor scale starts on G and follows the minor scale pattern.
Here's what each G scale looks like on the low E string
If we write out the notes for each scale we can see that there is quite a bit of overlap:
G Major: G A B C D E F#
G Minor: G A A# C D D# F
You can see that they share many notes with the only differences being A# instead of B, D# instead of E, and F instead of F#.
The gaps between notes are called intervals and they are built from a quality and a number. Examples are: Major(quality) 2nd(number) and Perfect(quality) 5th(number).
| Interval | No. of Semitones | Note in Root of G |
|---|---|---|
| Minor 2nd | 1 | G# |
| Major 2nd | 2 | A |
| Minor 3rd | 3 | A# |
| Major 3rd | 4 | B |
| Perfect 4th | 5 | C |
| Diminished 5th | 6 | C# |
| Perfect 5th | 7 | D |
| Minor 6th | 8 | D# |
| Major 6th | 9 | E |
| Minor 7th | 10 | F |
| Major 7th | 11 | F# |
| Perfect Octave | 12 | G |
Now that we understand notes and intervals we can use those building blocks to start looking at chords. The simple beginner chords are built using note combinations called triads. A triad is a three note combination that makes up chords. They are based on the root note plus 2 additional notes that can be found using different intervals.
Now, since you can't play multiple notes on the same string, chords require us to use multiple strings to get all the necessary notes. Depending on the chord, we may have to hold down multiple strings at the same time. Let's see what that looks like in practice. We'll start with an easy one: E Major (or just E. The Major is implied)
The image above is called a chord diagram. If we look at each string and which frets are being held down we can see that the notes in the E chord are:
E(open), B(2nd fret), E(2nd fret), G#(1st fret), B(open), E(open)
Now, let's compare that to the notes in the E major scale. Remember, we can build a major diatonic scale with the pattern: W-W-H-W-W-W-H. So, for E major that would look like this:
E, F#, G#, A, B, C#, D#
I've bolded the notes of the E major chord and you can see they all exist in the major scale.
The same is true of E minor:
Notes: E(open), B(2nd fret), E(2nd fret), G(open), B(open), E(open)
And now the E minor scale (W-H-W-W-H-W-W)
E, F#, G, A, B, C, D
As with the major chord, the notes of the minor chord all exist in the E minor scale.
A few things to notice here.
The only difference between the E major and E minor chords is that E major has a G# and E minor has a G. Everything else is the same.
In both chords, there are repeated notes (the E and B in both cases). This is called doubling and you can have either an octave doubling which is when the same note is played at different octaves or unison doubling when it's the same note at the same octave.
If you’re looking at any given scale, a chord can be made by using each note in the scale as the root. These are usually notated with roman numerals like this:
I, II, III, IV, V, VI, VII
For a given scale you would use uppercase and lowercase to indicate whether it’s a major or minor chord.
This happens because you build each chord by taking the root + 3rd + 5th. Depending on where those notes land it could be a major or a minor chord. This is due to the fact that the scale's step pattern is not uniform.
As an example let’s stay in the G Major Key.
That scale is: G-A-B-C-D-E-F#
So, the chord for A is: A(root), C(3rd), E(5th)
As discussed above, simple chords are built with triads. The major and minor chords are built like this:
If we start at A on the fretboard and move to the next note in the chord (C) that is only 3 frets away so it’s a MINOR 3rd instead of a major so the chord is minor which is why for G Major Key the notation is:
I, ii, iii, IV, V, vi, vii°
In this article I attempted to cover some entry-level music theory as it applies to learning the guitar. We covered the basics of notes scales and simple chords which is about as far as I've gotten on my journey to date.