Why Is the Guitar Tuned E-A-D-G-B-E?

The short answer: standard tuning is a compromise between two competing goals — making scales easy (which wants equal spacing between strings) and making chords easy (which wants notes of common chords to fall under four fingers). Tuning mostly in fourths with one major third between G and B strings is the sweet spot musicians settled on centuries ago.

The structure: fourths with a kink

Check the gaps between adjacent strings:

E → A: perfect fourth (5 semitones)
A → D: perfect fourth
D → G: perfect fourth
G → B: major third (4 semitones) ← the kink
B → E: perfect fourth

That one smaller gap is why every pattern you learn — octave shapes, scale boxes, chord shapes — bends by one fret when it crosses the B string. It's not you. It's the tuning.

Why not tune in all fourths?

All-fourths tuning (EADGCF) exists, and some players — mostly jazz and fusion — swear by it. Every scale pattern becomes identical across all strings. Sounds perfect, right?

The problem is chords. With all fourths, the familiar open chords — the cowboy chords every song is built on — become awkward stretches or impossible. Try voicing an open C major or a first-position E major in all-fourths and your fingers file a complaint.

The major third between G and B pulls chord tones closer together, so a full six-string E major chord needs exactly zero difficult stretches. The tuning trades a little scale-pattern consistency for a lot of chord playability. Given that most guitar playing is chords, it's a good trade.

Why fourths at all? Blame your hand

Four frets is about what four fingers can cover comfortably. A perfect fourth between strings means one hand position covers all the notes in between with no gaps and minimal overlap. Tune wider (fifths, like a violin family instrument scaled up) and you'd need constant position shifts; tune narrower (thirds all the way) and you'd get lots of redundant overlap and need more strings to cover the same range. The lute players of the Renaissance worked this out long before electric guitars, and the design survived because hands haven't changed.

The practical consequences you live with daily

Octave shapes shift at the B string. From the E or A strings, an octave is 2 strings up + 2 frets over; cross into the B string and it becomes 3 frets. See octave shapes on guitar.
Scale patterns bend. Every box pattern nudges notes on the B string one fret up. Explained in major scale patterns.
The same interval looks different on different string pairs. Which is why learning interval shapes per string-pair matters.

Once you know the kink exists, it stops being random. There's exactly one exception to every rule, it always lives at the B string, and it's always one fret.