Guido d’Arezzo (literally, Guido of Arezzo, which is a town in Tuscany) was a Benedictine monk who lived during what is today called the Medieval Period.  Guido is often referred to as the “Father of Music Education” and he is perhaps the most influential musician in history that you’ve never heard of.  He was a musician, a teacher, and a music theorist, and he was widely known (among his musical contemporaries) during his own lifetime as the author of Micrologus, a treatise on teaching and singing Gregorian Chant and the composition of polyphonic music.

It was Guido who chose the solmization syllables that evolved into the system of solfège we use today.

The original syllables were:

ut re mi fa sol la si

The first six syllables come from the first syllable in each line of the Latin hymn Ut queant laxis (Hymn to John the Baptist).

Ut queant laxis
Resonare fibris,
Mira gestorum
Famuli tuorum,
Solve polluti
Labii reatum,
Sancti Iohannes.

Each of the first six lines of this hymn begins on a note a step higher than the note the previous line began with.

“UT QUEANT LAXIS” FROM A CONTEMPORARY COPY OF THE ANTIPHONALE MONASTICUM ~ TRADITIONAL GREGORIAN CHANT NOTATION IS WRITTEN IN NOTES SUNG ON A SINGLE SYLLABLE CALLED “NEUMES” ON A FOUR-LINE STAFF

For the seventh note of the diatonic scale, subsequent convention chose the syllable si, a contraction of the first two initials in Sancte Iohannes (Saint John).  Originally Latin had no letter J.