Everything You Need to Know.

1. Notes and the Chromatic Scale

Western music uses 12 notes. That's it. Every melody, every chord, every song you've ever heard is built from these 12 pitches, repeated at higher and lower octaves.

The distance between any two adjacent notes is called a semitone (or half step). Two semitones make a whole tone (or whole step). On guitar, one semitone equals one fret.

Sharps, flats, and enharmonic equivalents

Some notes have two names. C# and Db are the same pitch played on the same fret. These twin names are called enharmonic equivalents:

Which name you use depends on the musical context (the key you're in). The rule of thumb: each letter name appears once per scale, so you pick whichever spelling avoids duplicates.

Octaves

After the 12th note, the pattern repeats. The next C sounds like the first C but higher. This repetition is called an octave. On guitar, moving 12 frets up on the same string brings you one octave higher.

2. Intervals

An interval is the distance between two notes, measured in semitones. Intervals are the DNA of music. Every scale is a pattern of intervals. Every chord is a stack of intervals. Understand intervals and you understand everything.

Compound intervals

Intervals wider than an octave are called compound intervals. These are the 9th, 11th, and 13th you see in jazz chord names. They're simply the 2nd, 4th, and 6th played one octave higher:

Why intervals matter for guitar

On guitar, shapes are portable. If you learn that a major 3rd is always 4 frets, you can find it anywhere on the neck. Intervals let you think in relationships instead of memorizing note names for every position.

3. Scales

A scale is a selection of notes from the 12 available, arranged in a specific interval pattern. Scales give music its flavor. The same melody played over a major scale sounds completely different over a minor scale.

The major scale

The most fundamental scale. Its pattern of whole (W) and half (H) steps is:

Seven notes, seven intervals from the root. Every major scale follows this exact same pattern, regardless of the starting note.

The natural minor scale

The minor scale has a darker sound. Its formula:

Notice that A minor and C major use exactly the same notes. They're relative to each other. Every major key has a relative minor starting 3 semitones below.

Harmonic and melodic minor

The harmonic minor raises the 7th degree by one semitone, creating a leading tone that pulls strongly to the root. This is where the "exotic" or "Spanish" sound comes from.

The melodic minor raises both the 6th and 7th degrees, smoothing out the awkward gap in the harmonic minor. Jazz musicians use it extensively.

Pentatonic scales

Remove two notes from a major or minor scale and you get a pentatonic (five-note) scale. The minor pentatonic is the most common scale in rock and blues guitar:

Pentatonic scales sound good over almost anything because they avoid the two notes that create the most tension (the 2nd and 6th degrees of the natural minor). That's why they're usually the first scale guitarists learn for improvisation.

The blues scale

Take the minor pentatonic and add one note: the blue note (b5 / #4). You get six notes and that classic blues sound:

4. Modes

Modes are scales built by starting on each degree of the major scale. Same seven notes, different starting point, completely different musical character.

The practical way to think about modes: each one is a modification of either the major or minor scale. Dorian is minor with a raised 6th. Mixolydian is major with a lowered 7th. Lydian is major with a raised 4th.

When to use modes

Modes aren't just academic. Dorian is all over funk and jazz. Mixolydian dominates classic rock. Phrygian shows up in metal and flamenco. Once you hear the character of each mode, you start recognizing them everywhere.

5. Chords

A chord is three or more notes played together. Chords are built by stacking intervals on top of a root note. The intervals you choose determine the chord type.

Triads

The simplest chords. Three notes: root, 3rd, 5th. The quality of the 3rd and 5th determines the triad type:

These four triad types are the foundation of all harmony. Every other chord is an expansion of one of these.

Seventh chords

Add a fourth note (the 7th) and triads become seventh chords. These are the bread and butter of jazz and sophisticated pop:

Power chords

A power chord is just root + 5th (sometimes with the octave). No 3rd means no major/minor quality. That's why power chords work with distortion: the simplicity avoids "mud." Technically they're not even full chords (only two distinct notes), but they're fundamental to rock and metal guitar.

6. Extensions, Alterations, and Suspensions

Extensions (9, 11, 13)

Stack more intervals on top of a seventh chord and you get extended chords. They add color and sophistication:

On guitar, you can't play all those notes. Guitarists routinely omit the 5th, sometimes the root, and often inner extensions. A "C13" on guitar might only use four or five notes. This is normal and expected.

Alterations

Sharping or flatting an extension creates an altered chord. These are common in jazz:

Suspended chords

Replace the 3rd with the 2nd or 4th and the chord loses its major/minor identity. It suspends resolution:

Add chords vs. extended chords

Cadd9 = triad + 9 (no 7th). C9 = seventh chord + 9 (includes the 7th). The "add" means you're inserting one extra note without implying a full extension stack.

7. Harmony and Chord Functions

Harmony is the study of how chords relate to each other within a key. Not all chords in a key have the same role. Some feel like home. Some create tension. Some pull you toward resolution.

Harmonizing the major scale

Build a triad on each degree of the major scale using only notes from that scale. You get seven chords, each with a natural quality:

The three harmonic functions

Every chord in a key serves one of three functions:

• Tonic (I, iii, vi): Stability. Home base. Resolution.
• Subdominant (ii, IV): Movement. Departure from home.
• Dominant (V, vii°): Tension. The pull back to tonic.

Most music follows the pattern: Tonic → Subdominant → Dominant → Tonic. Understanding this cycle is the key to writing progressions that work.

Harmonizing with seventh chords

Add the 7th to each diatonic chord and you get richer harmonies. In C major:

Notice that only one chord is a dominant 7th (G7 on the 5th degree). This is a powerful identifier: in any major key, the chord that wants to resolve most is the V7.

8. Chord Progressions

A chord progression is a sequence of chords. Most popular music uses a handful of progressions, written in Roman numerals so they work in any key.

Common progressions

Why Roman numerals?

Roman numerals describe function, not pitch. "I V vi IV" is the same progression in every key. Learn the numbers and you can instantly transpose any song: just swap the key, the function stays identical.

9. The Circle of Fifths

The circle of fifths is a diagram that arranges all 12 keys by the interval of a perfect 5th. Moving clockwise, each key adds one sharp. Moving counter-clockwise, each key adds one flat.

What the circle tells you

• Key signatures: How many sharps or flats a key has.
• Closely related keys: Adjacent keys on the circle share the most notes. Modulating between them sounds smooth.
• Relative minor: The inner ring of the circle shows each major key's relative minor (e.g., C major / A minor).
• Chord relationships: The I, IV, and V of any key are always three adjacent positions on the circle.

Practical use

If you're jamming in C major and someone says "go to the IV," you look one step counter-clockwise on the circle: F. The V is one step clockwise: G. The circle makes key navigation instant.

10. Chord Substitutions

A chord substitution replaces one chord with another that serves a similar harmonic function. Substitutions add variety and sophistication without breaking the progression.

Diatonic substitution

Replace a chord with another chord that shares the same function. Since iii and vi are both tonic substitutes, you can swap Em for Am in the key of C. Since ii and IV are both subdominant, Dm can replace F.

Secondary dominants

Any chord can be preceded by its own V7. In C major, if you're going to Am (vi), you can insert E7 before it. E7 is the "V of vi":

Secondary dominants create momentary key changes that add forward momentum.

Tritone substitution

A dominant 7th chord can be replaced by the dominant 7th a tritone (6 semitones) away. G7 resolving to C can become Db7 resolving to C. This works because the two chords share the same tritone interval (B and F):

This is one of the most important techniques in jazz harmony.

Borrowed chords (modal interchange)

Borrow a chord from the parallel minor (or other parallel mode). In C major, using Fm (IV from C minor) instead of F creates a darker, unexpected color. The bVII (Bb in C major) is another common borrowed chord, used everywhere in rock.

11. Voice Leading

Voice leading is the art of moving from one chord to the next with minimal motion in each voice (note). Good voice leading makes chord changes sound smooth and connected instead of choppy and disconnected.

The principles

• Common tones: If two chords share a note, keep it on the same string/pitch.
• Stepwise motion: Move other notes by the smallest interval possible (one or two semitones).
• Contrary motion: When one voice goes up, another goes down. This creates independence between parts.
• Avoid parallel fifths: Two voices moving in parallel perfect 5ths sounds hollow. Classical rule, but worth knowing.

Voice leading on guitar

On guitar, voice leading is about choosing voicings that are physically close on the neck. Instead of jumping between open chords and barre chords, use inversions and partial voicings that keep the same fret area. The result: smoother, more musical chord transitions.

This is exactly what separates a beginner strumming open chords from a skilled player using voice-led voicings.

12. The Guitar Fretboard

The guitar fretboard is a grid. Six strings, each tuned to a different note. Each fret raises the pitch by one semitone. Every note exists in multiple locations.

Standard tuning

The intervals between adjacent strings are: perfect 4th (5 semitones) everywhere except between G and B, which is a major 3rd (4 semitones). This irregularity is why chord shapes shift when crossing the G-B boundary.

Finding any note

Fret 0 (open) is the string's note. Each fret adds a semitone. The 12th fret is always the same note as the open string, one octave higher. Knowing the open strings and counting semitones lets you find any note anywhere.

Movable shapes

Because guitar is laid out in a grid of equal intervals, chord and scale shapes are movable. An E major chord shape moved up two frets (with a barre) becomes F# major. Same shape, same intervals, different root. This is the guitar's superpower compared to piano.

Inversions on guitar

A chord inversion puts a note other than the root in the bass. C/E means C major with E as the lowest note. On guitar, this usually means choosing a voicing where a different string carries the bass note. Inversions are essential for good voice leading.

13. Tunings and Capo

Alternate tunings

Changing the open-string pitches creates new possibilities. Some popular alternate tunings:

Each tuning changes which chord shapes are easy and which are hard. An open tuning makes one chord effortless (just strum all strings) but may make others more difficult.

Capo

A capo clamps across all strings at a given fret, effectively raising every open string by that many semitones. A capo on fret 2 turns standard tuning into F# B E A C# F#.

The practical use: play familiar open chord shapes in a different key. Capo on fret 3 and play a G shape? You're actually playing Bb. Capo on fret 5 and play a C shape? That's an F.

Capo is especially useful for singers who need a song transposed to match their vocal range without learning new chord shapes.

14. Putting It All Together

Music theory is not a set of rules. It's a vocabulary for describing what you hear. Here's the chain of knowledge, from foundation to application:

Every concept on this page feeds the next. Intervals build scales. Scales build chords. Chords build harmony. Harmony tells you why a song works. And the guitar fretboard is the instrument where you bring it all to life.

Ready to apply it? Explore the tools that compute all of this for you.