Western music uses 12 notes, repeating in octaves:

Each step is a semitone (one fret on guitar). Two semitones = one whole tone.

There is no sharp between E–F and B–C — these are natural semitones.

An interval is the distance between two notes, measured in semitones:

The 3rd determines major vs minor quality. The 5th gives chords their stability.

A scale is a set of notes in order. The two most important:

Major scale (happy/bright) — W W H W W W H

Natural minor scale (sad/dark) — W H W W H W W

W = whole step (2 frets), H = half step (1 fret). Notice C major and A minor share the same notes — they are relative to each other.

The pentatonic scale uses 5 notes instead of 7. It's the most common scale for guitar solos and improvisation.

Minor pentatonic — 1 b3 4 5 b7

Major pentatonic — 1 2 3 5 6

The minor pentatonic is the foundation of blues, rock, and most guitar solos. Box 1 (frets 5–8 in Am) is the first shape every guitarist learns.

A chord is 3+ notes played together. The most basic chord is a triad (3 notes):

Add a 7th note to get seventh chords: maj7, min7, dom7 (the "blues" chord), etc.

Instead of note names, chords are written as numbers relative to the key:

Uppercase = major, lowercase = minor. In the key of C:

This lets you talk about chord progressions in any key. "I–V–vi–IV" is the most popular progression in pop music (C–G–Am–F in key of C).

In 4/4 time (the most common), one measure has 4 beats:

Downstrokes fall on the beat (1, 2, 3, 4). Upstrokes fall on the "and" (&) between beats. Count: "1 & 2 & 3 & 4 &".

Standard tuning (low to high): E A D G B e

Each fret is one semitone higher. Key landmarks:

The 5th fret rule: the 5th fret of any string sounds the same as the next open string (except G string → B string, which is the 4th fret).