Guitar Theory: The Complete Beginner’s Guide

It's so important for every guitar player to have at least a basic understanding of guitar theory—that is, how music theory relates to the guitar.

Guitar theory shouldn't be boring, because it describes how things work and gives us rules that we can use to make great sounding music. When we pair a bit of theory together with a bit of skill on the guitar, great things can happen.

Now, I know some people say guitar theory is useless—and I get where they're coming from. If you're just memorizing abstract concepts without applying them, then yeah, it's pretty pointless. But when you understand why things work the way they do, suddenly the fretboard starts to make sense. You stop feeling lost. You start making music instead of just playing notes.

The easiest way to understand guitar theory is by learning the number system. You'll find quite a few references to that in the lessons on this page, but I go into far more detail on that in my Guitar Theory Unlocked course which I really encourage you to check out. You'll likely be surprised how learning some basic music theory can really change the way you approach your guitar!

Alright, do you have your guitar in hand? Let's get started.

How to use this guide: Think of this page as your roadmap. I'll introduce each major concept and show you how they all connect. When you want to go deeper on any topic, follow the links to my detailed lessons. Bookmark this page—you'll probably come back to it as your playing develops.

What IS Guitar Theory?

Before we dive in, let's get clear on what guitar theory actually is.

Guitar theory is simply music theory as it applies to the guitar. It's the "why" behind everything you play. Why do certain chords sound good together? Why does this scale work over that chord progression? Why does moving this shape up two frets give you a different chord?

The beautiful thing about theory is that once you understand it, you don't have to memorize as much. Instead of memorizing hundreds of individual chords, you understand the system behind them. Instead of learning scales as random patterns, you see how they connect across the entire fretboard.

Think of it like this: music is a language. Theory gives you the grammar and vocabulary. You could memorize phrases in a foreign language and get by, but if you understand the grammar, you can create your own sentences. Same thing with guitar.

Understanding Notes and the Fretboard

Everything in guitar theory builds on one foundation: knowing your notes.

The Musical Alphabet

Music uses just seven letters: A, B, C, D, E, F, and G. After G, we start over at A. That's it. But between most of these notes, we have sharps and flats (the black keys on a piano). On guitar, these are the frets between the "natural" notes.

Tones and Semitones

The distance between two notes is measured in tones and semitones. A semitone is one fret on your guitar. A tone is two frets. Understanding tones and semitones is crucial because it's how scales and chords are built.

Here's the pattern of natural notes:

A to B = 1 tone (2 frets)
B to C = 1 semitone (1 fret)
C to D = 1 tone
D to E = 1 tone
E to F = 1 semitone (1 fret)
F to G = 1 tone
G to A = 1 tone

Notice B to C and E to F are only one fret apart. This is important—it's why the fretboard looks the way it does.

Learning the Fretboard

Do you truly understand your fretboard? Most guitarists don't, and that's a big reason they feel stuck.

The good news is you don't need to memorize every single note on every single fret right away. Start with the notes on the 6th and 5th strings. These are your root notes for bar chords—once you know them, you can find any chord anywhere on the neck.

Root Notes: The Foundation of Everything

If there's one concept that unlocks everything else, it's understanding root notes.

The root note is the note that gives a chord its name. If you're playing a G chord, the root note is G. If you're playing a D chord, the root note is D. Simple as that.

In most standard chords, the root note is also the lowest-pitched note. This matters because lower frequencies set the stage for how our ears interpret everything above them. Think of the root note as the anchor—it tells your ear "this is a G chord" or "this is a D chord."

Why This Matters for Your Playing

Once you know where the root note is in each chord, you know:

Which strings to strum (don't go lower than the root!)
How to move chords around (move the root, move the chord)
How bar chords work (the root position tells you the chord name)

Take the D chord, for example. The root note is on the 4th string—that open D. The 5th and 6th strings? They don't belong. The low E especially will clash and make your chord sound muddy. The root note tells you where to start your strum.

How Chords Are Built

Now that you understand root notes, let's look at how chords are actually constructed. This is where theory gets really practical.

The Magic of Thirds

A basic chord—called a triad—is built from just three notes: the root, the third, and the fifth. These numbers come from the major scale. If you start on any note and count up to the 3rd and 5th notes of its scale, you've got your chord.
The third is what determines whether a chord is major or minor:

Major third = happy, bright sound
Minor third = sad, darker sound

That's really the difference between major and minor chords—just one note, moved by one fret.

Triads on the Guitar

Triads are incredibly useful because they're compact. You don't always need to play a full 5 or 6 string chord. Sometimes just three notes is perfect—especially when you're playing with other musicians or want to add some color to your rhythm playing.

I've done a whole series on triads using the top three strings:

Once you understand these shapes, you can play any major or minor chord anywhere on the neck using just three strings. The beauty of that is you can start throwing them into licks, creating movement, making two strings sound amazing—all kinds of possibilities open up.

If you want to explore more, check out having fun with triads where I show some cool applications using open D and Dm patterns.

You can even start creating your own guitar chords once you understand how they're built.

How Chords Are Built

Let's talk about the chord shapes you'll use most often.

Open Chords

Open chords use open strings and are played in the first few frets. They're the first chords most guitarists learn, and for good reason—they sound full and rich, and they're relatively easy to play.

If you're just getting started, check out my beginner's guide to open chords. The most essential ones to know are G, C, D, E, A, and their minor versions.

The G, C, and D chords alone will let you play hundreds of songs. Seriously—those three chords are probably responsible for more hit songs than any others.

Bar Chords

Here's where root note knowledge really pays off.

Bar chords are moveable shapes. You take an open chord shape, use your index finger to bar across the strings (replacing the nut), and now you can move that shape anywhere on the neck.

The two most important bar chord shapes are:

E-form (root on 6th string)
A-form (root on 5th string)

If you know an E major shape, you can play ANY major chord by moving it to the right fret. Move the root note to the 3rd fret of the 6th string? That's G major. Move it to the 5th fret? A major. 8th fret? C major.

This is what I mean when I say theory reduces what you need to memorize. You don't need to learn 12 different major chord shapes—you learn ONE shape and move it around.

Now, I know some people struggle with bar chords. "I hate bar chords!" is something I hear all the time. If that's you, don't give up. Check out don't play bar chords like THIS for some common mistakes to avoid, and bar chords made simple for a better approach.

Once you get them down, you can learn 48 chords in 9 minutes—not because you're memorizing 48 things, but because you understand how the system works.

Try this: Play an E major chord. Now slide that entire shape up to the 5th fret, using your index finger to bar across all six strings at the 5th fret. That's A major. Same shape, different root note position. Now try the 7th fret—that's B major. You just played three chords with one shape.

The Number System and Keys

This is where everything starts to click together.

What Is a Key?

A key is simply a family of notes and chords that sound good together. When someone says "this song is in the key of G," they're telling you which notes and chords will work.

Every major key has seven chords that belong to it. In the key of G, those chords are: G, Am, Bm, C, D, Em, and F#dim. You don't need to memorize every key's chords—you just need to understand the pattern.

The Number System

Instead of thinking in letter names, think in numbers:

1 (I) = the "home" chord (also called the tonic)
4 (IV) = the fourth chord in the key
5 (V) = the fifth chord in the key
6 (vi) = the sixth chord (usually minor)
And so on...

Why is this useful? Because chord progressions follow patterns, and those patterns work in ANY key.

A 1-4-5 progression in G is: G - C - D
A 1-4-5 progression in A is: A - D - E
A 1-4-5 progression in C is: C - F - G

Same pattern, different key. Once you know the pattern, you can play it anywhere.

Try this: Play G - C - D. That's 1-4-5 in the key of G. Now play the same pattern in A: A - D - E. Same 1-4-5, different key. Try it in C: C - F - G. Feel how the relationship between the chords stays the same even though the actual chords change? That's the power of the number system.

The most popular chord progression of all time is probably the 1-5-6-4 (think "Let It Be," "No Woman No Cry," countless others). Learn it in one key, and you can play it in all of them.

Common Progressions You Should Know

Here are a few progressions worth having in your back pocket:

1-4-5 (The Blues/Rock Standard)
The backbone of rock and roll, blues, and country. In G: G - C - D.

1-5-6-4 (The Pop Progression)
Used in hundreds of hit songs. In G: G - D - Em - C.

1-6-4-5 (The Doo-Wop)
Classic 50s sound, but still used today. In G: G - Em - C - D.

2-5-1 (The Jazz Turnaround)
The most important progression in jazz. In G: Am - D - G.

Check out my 10 popular guitar chord progressions lesson—once you see these patterns in action, you'll start recognizing them everywhere.

Adding Color to Your Progressions

Once you know the basic progressions, you can start spicing them up. Try adding drone notes to your chord progressions for a richer sound. Or work in some chord embellishments to add movement and interest.

Even something as simple as the Em to G embellishment riff can transform a boring chord change into something musical.

You can also explore different voicings of the same chords. I did a lesson on 13 ways to spiff up a G chord—same chord, tons of different flavors. Or check out E minor chord alternate voicings for some variations you've probably never seen.

Finding the Key of a Song

Want a quick trick? Here's 1 trick to figuring out the key of a song: the key is usually the chord that feels like "home"—the one the song resolves to and feels most at rest on.

Once you know the key, you know which chords and scales will work. That's powerful.

Transposing to Different Keys

What if you know a song in G but the singer needs it in A? This is where the number system really shines.

If you know the progression is 1-4-5 in G (G-C-D), just find 1-4-5 in A (A-D-E). Same progression, different key.

Using a capo makes this even easier. Learn how to transpose chords with a guitar capo—it's one of the most practical skills you can have, especially if you play with singers.

Chords That Work Together

Once you know the key, you know which chords will sound good. In the key of C, for example, here are chords that work together in C: C, Dm, Em, F, G, Am, and Bdim.

You don't need to use all of them—most songs use just 3 or 4. But knowing which chords belong to a key means you'll never grab a wrong chord again.

Scales

Scales are the raw material for melody and soloing. If chords are the harmony, scales are what you use to create melodies on top.

What Is a Scale?

A scale is simply a collection of notes arranged in a specific pattern. Different scales have different sounds—major scales sound happy and bright, minor scales sound darker and more emotional.

You might wonder, how many guitar scales are there? The answer is... a lot. But here's the good news: you really only need to know a few to cover most situations.

The Pentatonic Scale

If you only learn one scale, make it the pentatonic. Learning the pentatonic scale will take you incredibly far.

The pentatonic is a five-note scale (penta = five) that works over almost everything. It's the foundation of rock, blues, country, and pop soloing. The reason it's so versatile is that it leaves out the "problem" notes that might clash with certain chords.

Try this: Learn the A minor pentatonic at the 5th fret—it's the most common position.

Now put on any rock or blues backing track in A minor and just noodle around with those five notes. You'll notice that nothing sounds "wrong." That's the beauty of the pentatonic.

Once you've got the basic shape down, you can start having fun with pentatonic riffage—using the scale to create actual musical ideas, not just running up and down patterns.

The Major and Minor Scales

The full major and minor scales have seven notes each. They give you more options than the pentatonic, but they're also a bit trickier to use because those extra notes can clash if you're not careful.

Check out:

Connecting Scale Patterns

Here's where a lot of guitarists get stuck: they learn one scale pattern and just play it over and over in one position.

The fretboard has the same notes all over it—you just need to learn how to connect guitar scale patterns so you can move freely up and down the neck.

Once you can do that, you can run up the fretboard in a single lick and really start to sound like you know what you're doing.

Intervals: The Secret Sauce

Intervals are the distance between two notes, and they're the secret ingredient that makes your playing sound more musical.

What Are Intervals?

You already know some intervals: the root and the third make a chord major or minor.

The root and the fifth add power. But intervals go way beyond chord construction—they're also what makes melodies interesting.

Different intervals have different sounds:

Thirds = sweet, melodic (major or minor feeling)
Fourths = strong, open (think "Here Comes the Bride")
Fifths = powerful, stable (power chords are just root + fifth!)
Sixths = smooth, soulful

Using Intervals in Your Playing

Joe Bonamassa LOVES thirds—and for good reason. Thirds are one of the most musical sounds you can get on guitar.

Check out these lessons to start incorporating intervals into your playing:

I've also got some "lick of the week" lessons that focus on intervals:

Once you start thinking in intervals instead of just scale patterns, your solos will have a lot more melody to them.

Try this: Play the 5th fret on the 4th string (that's a G). Now play the 4th fret on the 3rd string (that's a B). Those two notes together are a third—and they sound sweet, right? Now slide both notes up two frets. Still a third, different notes. That's how intervals work—it's the distance that creates the sound, not the specific notes.

Beyond the Basics

Once you've got the fundamentals down, there's a whole world of more advanced concepts to explore.

Chord Inversions and Slash Chords

An inversion is when you play a chord with a note other than the root as the lowest note. This creates a different flavor—same chord, different feel.

Guitar chord inversions are great for creating smooth bass lines between chords. And the #1 slash chord on guitar? That's D/F#—it creates a beautiful walking bass line from G to D.

Arpeggios

What are guitar arpeggios? They're the notes of a chord played one at a time instead of all together. Arpeggios are incredibly useful for soloing because they outline the chord changes—they're basically a roadmap showing you which notes will sound best at any given moment.

Modes

Modes are variations of the major scale, each starting on a different note. They have exotic names like Dorian, Mixolydian, and Phrygian.

Here's my honest take: how to skip learning the modal system. For most guitarists, especially early on, modes are more confusing than helpful. Focus on the fundamentals first. Once those are solid, you can explore modes if you want—but you might find you don't need them as much as you thought. Some people even ask are guitar modes outdated?

Putting It All Together

So you've got your open chords down... what's next?

Here's the path I recommend:

Solidify your open chords and learn to change between them smoothly
Learn the notes on the 6th and 5th strings so you can find any root note
Master a few bar chord shapes so you can play any chord anywhere
Understand the number system so chord progressions make sense
Learn the pentatonic scale in at least two positions
Start connecting everything—use your theory knowledge to understand why things work

The weird thing about guitar theory is that once you know it, you almost forget you know it. It becomes automatic. You stop thinking "I need to play the 4 chord" and just... play it. That's the goal.

Want to Go Deeper?

If you've made it this far, you're clearly serious about understanding guitar theory. That's great—this knowledge will serve you for the rest of your playing life.

But reading about theory is different from applying it. What really makes theory stick is working through it systematically, with clear examples and practice exercises.

That's exactly what I built Guitar Theory Unlocked to do. It's my complete course that takes you from confused to confident, step by step. You'll understand the number system inside and out, know how to build any chord, and actually use theory to make better music—not just understand it in the abstract.

If you're ready to finally make sense of the fretboard, check it out. I think you'll be surprised how quickly things click.

Guitar Theory Lessons

Explore all of my guitar theory lessons below: