Music History · Guido d’Arezzo

Guido d’Arezzo — The Man Who Deleted a Note

From Dead Sea Scales: The 5 Missing Notes™ by Christopher Dean

Around 1030 CE, a Benedictine monk named Guido d’Arezzo changed music forever. He invented solfege — Do, Re, Mi, Fa, Sol, La — to teach monks to sight-sing hymns. He also invented the musical staff and the Guidonian hand, a system of mapping notes to finger joints for memorization.

But the most important thing Guido did was leave out a note.

Why Only 6 Notes?

Guido’s hexachord has 6 notes, not 7. He deliberately removed the 7th degree (B) because it created a tritone against F — the interval medieval musicians called diabolus in musica, the Devil in music. His solution was subtraction: remove the problem note entirely.

In the Dead Sea Scales framework, Guido’s hexachord is Ionian minus the 7th degree — what we call a Guido Hexatonic. It produces 6 modes (no Locrian, because removing the 7th eliminates the Locrian position). This is a Deleted Diatonic — one of three types of scale created by removing notes from the major scale instead of adding them.

The Three Deleted Diatonics

Type	What’s Deleted	Modes	Historical Origin
Hexatonic	4th degree	6 (no Lydian)	Various folk traditions
Guido Hexatonic	7th degree	6 (no Locrian)	Guido d’Arezzo, 1030 CE
Pentatonic	4th + 7th	5 (no Lydian, no Locrian)	Universal — every culture on Earth

The pentatonic scale — the most universal scale in human music — is both deletions combined. Remove the two notes that create the tritone and you get the 5-note scale that appears independently in Chinese, Japanese, African, Celtic, Native American, and dozens of other musical traditions.

Guido in the Dead Sea Scales Framework

Guido didn’t just teach singing. He performed the first documented Deleted Diatonic operation — a thousand years before anyone had a name for it. His hexachord sits in the Dead Sea Scales system as one of 17 Deleted Diatonic modes, alongside the hexatonics and pentatonics.

Guido taught us 6 notes. George Russell recentered the tonal universe. Dead Sea Scales finished the map.

— Christopher Dean, Dead Sea Scales