Intervals
The building blocks of every chord and scale you'll ever play.
What Is an Interval?
An interval is the distance between two notes. That's it. It's music theory's ruler. Every chord you play, every scale you run, every melody you hum. They're all built from intervals.
On the guitar, intervals have a beautifully simple physical meaning: the number of frets between two notes. Each fret is one semitone — the smallest step in Western music.
One fret = one semitone. Two notes 4 frets apart are separated by an interval of 4 semitones.
Let's see this on the fretboard. Here's a C note on the 3rd fret of the A string, and an E note 4 frets higher at fret 7:
Why should you care? Because once you understand intervals, you can build any chord from any root note. You won't need to memorize hundreds of shapes — you'll understand the formula behind them.
What does an interval measure?