Guitar Chord Theory for Beginners

Stop memorizing chord shapes. Start understanding why chords work—and gain the power to build any chord yourself.

What Actually IS a Chord?

A chord is three or more notes played together. That's the entire definition. But there's an elegant system behind which notes you choose.

The most basic chord—a triad—uses just three notes:

These numbers refer to scale degrees. If you're building a C chord, you use notes from the C major scale:

• C (1 - Root)
• E (3 - Third)
• G (5 - Fifth)

That's a C major chord. C-E-G. Three notes. One chord.

The Four Basic Triad Types

By adjusting the intervals between these three notes, you get four distinct chord sounds:

Triad Type	Formula	Intervals	Sound	Example (C)
Major	1 - 3 - 5	Root + Major 3rd + Perfect 5th	Happy, bright	C - E - G
Minor	1 - ♭3 - 5	Root + Minor 3rd + Perfect 5th	Sad, dark	C - E♭ - G
Diminished	1 - ♭3 - ♭5	Root + Minor 3rd + Diminished 5th	Tense, unstable	C - E♭ - G♭
Augmented	1 - 3 - #5	Root + Major 3rd + Augmented 5th	Dreamy, unresolved	C - E - G#

Why Guitar Chords Have More Than 3 Notes

You might be thinking: "Wait, when I play a G chord, I strum 6 strings—not 3!"

You're right. On guitar, we often double some of the notes in different octaves. A standard open G chord contains:

• String 6: G (root)
• String 5: B (3rd)
• String 4: D (5th)
• String 3: G (root - doubled)
• String 2: B (3rd - doubled)
• String 1: G (root - doubled again)

It's still just G-B-D—but spread across multiple octaves for a fuller sound.

Seventh Chords: Adding Depth

When you add a fourth note—the 7th—you get seventh chords. These are essential for jazz, blues, R&B, and modern pop.

Chord Type	Formula	Symbol	Sound
Major 7th	1 - 3 - 5 - 7	Cmaj7, CΔ7	Dreamy, sophisticated
Dominant 7th	1 - 3 - 5 - ♭7	C7	Bluesy, wants to resolve
Minor 7th	1 - ♭3 - 5 - ♭7	Cm7, Cmin7, C-7	Mellow, jazzy
Minor 7♭5 (Half-Diminished)	1 - ♭3 - ♭5 - ♭7	Cm7♭5, Cø7	Tense, jazz standard
Diminished 7th	1 - ♭3 - ♭5 - 𝄫7	Cdim7, C°7	Very tense, passing chord

The Nashville Number System

Professional musicians often use numbers instead of letter names. This makes it easy to transpose songs instantly.

In any major key, the chords follow this pattern:

So in the key of G:

• I = G major
• ii = A minor
• iii = B minor
• IV = C major
• V = D major
• vi = E minor
• vii° = F# diminished

Common Chord Progressions

Most popular songs use the same handful of progressions. Here are the big ones:

The "Pop Progression" (I - V - vi - IV)

The "50s Progression" (I - vi - IV - V)

The "Blues Progression" (I - IV - I - V)

Building Any Chord: A Step-by-Step Method

Want to build a chord you've never seen before? Here's the process:

1. Identify the root note — This is the letter name (C, G, F#, etc.)
2. Determine the chord type — Major? Minor? Dominant 7th?
3. Apply the formula — Use the formulas from the tables above
4. Find the notes on the fretboard — Use FretTrain to visualize!

Example: Build a Bm7 chord

1. Root: B
2. Type: Minor 7th → Formula: 1 - ♭3 - 5 - ♭7
3. B major scale: B - C# - D# - E - F# - G# - A#
4. Apply formula: B - D (♭3) - F# - A (♭7)
5. Result: Bm7 = B, D, F#, A

Chord Inversions

When the root isn't the lowest note, you have an inversion:

• Root position: C-E-G (root on bottom)
• First inversion: E-G-C (3rd on bottom)
• Second inversion: G-C-E (5th on bottom)

Inversions are written with a slash: C/E means "C chord with E in the bass."

Guitar players use inversions constantly—many voicings you already know are inversions!

Next Steps

Now that you understand chord construction:

• Analyze songs you know — What chords are they using? What progression?
• Learn chord voicings — There are many ways to play the same chord
• Study triads across the neck — FretTrain's Triad Mode is perfect for this
• Experiment with substitutions — Try replacing a IV with a ii, or a V with a vii°